LIU Hong-Xia1, 2, 3, , LI Wen1, , ZHANG Xin-Yue1, LI Juan1, PEI Yan-Zhong1
1. Interdisciplinary Materials Research Center, School of Materials Science and Engineering, Tongji University, Shanghai 201804, China2. State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China3. University of Chinese Academy of Sciences, Beijing 100049, China
中图分类号:
TB34
文献标识码:
A
文章编号:
1000-324X(2019)03-0341-08
通讯作者: Corresponding author:LI Wen, associate professor. E-mail: liwen@tongji.edu.cn
收稿日期:2018-05-30
网络出版日期: 2019-03-20
版权声明:
2019 无机材料学报编委会 This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
作者简介:
Author:LIU Hong-Xia (1992-), female, candidate of PhD. E-mail:hongxliu@126.com
Ternary chalcogenides I-V-VI2 compounds attract extensive attentions for thermoelectric applications due to their intrinsically low lattice thermal conductivity. AgBiSe2, as one of a few n-type semiconductors among these compounds, shows the potential to be a promising thermoelectric material. Therefore, this work focuses on its thermoelectric properties. According to the phase diagram of Ag2Se-Bi2Se3 system, the single phase region of (Ag2Se)1-x(Bi2Se3)x allows x to be varied in the range of 0.4~0.62. This large variation of x suggests a tunability of carrier concentration for this material. A broad carrier concentration of 1.0×1019~5.7×1019 cm-3 for single phased (Ag2Se)1-x(Bi2Se3)x is obtained through a composition manipulation, which enables a comprehensive assessment on electronic transport properties based on a single parabolic band model with acoustic scattering. The highest carrier concentration obtained in this work, approaching to the theoretical optimal one, leads to a peak ZT of 0.5 at 700 K. This work offers a well understanding of its transport properties and underlying physical parameters determining the thermoelectric performance.
Keywords：thermoelectric material
;
thermoelectric properties
;
AgBiSe2
;
carrier concentration
;
SPB model
LIUHong-Xia, LIWen, ZHANGXin-Yue, LIJuan, PEIYan-Zhong. Thermoelectric Properties of (Ag2Se)1-x(Bi2Se3)x[J]. Journal of Inorganic Materials, 2019, 34(3): 341-348 https://doi.org/10.15541/jim20180249
Due to the increasingly environmental crisis, development of sustainable clean energy becomes a key challenge in global scientific research[1]. Based on the Seebeck effect, thermoelectrics could directly convert heat into electricity without involving any moving parts and emissions, which has been considered as a solution for the crisis[2,3,4,5,6]. The conversion efficiency of thermoelectric materials mainly depends on the thermoelectric figure of merit, ZT=S2T/ρ(kE+kL), where S,ρ, T,kE and kLare the Seebeck coefficient, the electrical resistivity, the absolute temperature, the electronic and lattice thermal conductivities, respectively. Thus, a high S, a low ρand a low (kE+kL) are expected for a superior ZT.
However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well.
Ternary chalcogenides I-V-VI2 compounds (where I=Cu, Ag or alkali metal; V=Sb, Bi; and VI=S, Se, Te) have aroused widespread interests for thermoelectric applications due to their intrinsically low kL stemming from the strong anharmonicity induced by lone s2 pair electrons of the group V cations[46]. So far, the study of their thermoelectric properties mainly focuses on the Ag-based compounds, particularly Ag(Sb/Bi)(Te/Se)2[23,47-55]. The peak ZTs of 2.0 and 1.2 for AgSbTe2 and AgSbSe2 have been realized through band engineering and carrier concentration optimization[48,56], respectively, which are considered as potentially lead-free alternatives for p-type PbTe.
As one of a few n-type semiconductors among this family of compounds, the crystal structure of AgBiSe2 transforms from hexagonal to rhombohedral and then to cubic with increasing temperature[57,58,59,60], as shown in Fig. 1(a). The cubic AgBiSe2 shows highly disorder at cation sites, which are beneficial for the low kL through the strong phonon scattering by point defects[61]. Recently, numerous efforts have been put on its thermoelectric performance. In order to enhance the power factor (S2/ρ), Nb-[52], Ge-[62], In-doping[63] at cation site or Te-[64], Cl-doping[65] at anion site are carried out, and an enhanced ZT up to 0.7 is obtained in single phase AgBiSe2 at 773 K. It is well known that a realization in the highest possible ZT, even using the successful strategies mentioned above, strongly depends on an optimization in carrier concentration[66,67,68]. Therefore, an investigation on the transport properties in a broad carrier concentration range, is essential to fully assess the potential for thermoelectric applications.
Fig. 1 Crystal structures for the different phases of AgBiSe2 (a) and phase diagram of Ag2Se-Bi2Se3 system (b)[57]
This work focuses on the systematic investigation of the thermoelectric properties of (Ag2Se)1-x(Bi2Se3)x alloys. A broad carrier concentration ranging from 1.0×1019 cm-3 to 5.7×1019 cm-3 is obtained through the control of x, which enables a comprehensive evaluation of the electronic transport properties based on a single parabolic band transport with acoustic scattering. Moreover, the underlying physics including the scattering mechanism, deformation potential coefficient, density-of-states effective mass and optimal carrier concentration are discussed in details. The work offers a fundamental understanding of the transport properties of (Ag2Se)1-x(Bi2Se3)x.
1 Experimental methods
Polycrystalline (Ag2Se)1-x(Bi2Se3)x(0.4≤x≤0.62) was synthesized using Ag2Se and Bi2Se3 as the starting materials. Both Ag2Se and Bi2Se3 were synthesized by sealing stoichiometric quantity of Ag (99.999%) and Se (99.999%), Bi (99.999%) and Se (99.999%) in vacuum quartz ampoules, melting at 1273 K and 1123 K for 4 h, respectively, quenching in cold water, and then annealing at 843 K for 3 d. The obtained Ag2Se and Bi2Se3 ingots were weighed according to the stoichiometric ratio, melted at 1173 K for 10 h and annealed at 843 K for 2 d. Pellet samples (>96% of the theoretical density) with ~12.0 mm in diameter were obtained by an induction heating hot press system at 800 K for 30 min under a uniaxial pressure of ~ 80 MPa.
The details of the electronic transports (Seebeck coefficient, electronic resistivity and Hall coefficient) measurements are given in the literature[69]. The thermal conductivity was estimated viaκ = dCpD, where d is the geometric density, Cp is the heat capacity, and D is the thermal diffusivity. Parameter D was measured using a laser flash technique with the Netzsch LFA457 system, and Cp was determined by the Dulong-Petit limit and assumed to be temperature independent. All the transport property measurements were carried out under helium atmosphere from 300 K to 700 K. The measurement uncertainty for each transport property (S, ρand κ) is about 5%.
Phase composition and microstructures were identified by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM, Phenom Pro) equipped with an Energy Dispersive spectrometer. The longitudinal (vL) and transverse (vT) sound velocities were measured on the pellet samples at room temperature using an ultrasonic pulse receiver (Olympus-NDT) equipped with an oscilloscope (Keysight). Infrared Fourier transform spectroscopy (Bruker Tensor 2) was used to measure the optical reflectance coefficient for estimating the optical band gap[70].
2 Results and discussion
According to the phase diagram of Ag2Se-Bi2Se3 system[57] (Fig. 1(b)), (Ag2Se)1-x(Bi2Se3)x shows a single phase region at x ranging from 0.4 to 0.62. This tunable composition in a broad range suggests an availability of carrier concentration tuning for thermoelectric (Ag2Se)1-x(Bi2Se3)x. Powder XRD patterns for (Ag2Se)1-x(Bi2Se3)x(0.4≤x≤0.62) are shown in Fig. 2. It is found that the single phase region confines x to be from 0.48 to 0.56, since Ag2Se and Bi2Se3 impurity phases are observed for the samples with x≤0.46 andx≥0.58, respectively. As shown in Fig. 3(a), the locally enlarged XRDpatterns for the samples with single phase (0.48≤x≤0.56) show that the diffraction peaks shift to higher angles with increasing x. The dependence of lattice parameters on x in Fig. 3(b) shows that both a and c decrease with increasing x, which can be understood by the introduction of cation vacancy as x>0.5.
Fig. 3 Locally enlarged XRD patterns (a) and composition dependent lattice parameters (b) for the samples with 0.48≤x≤0.56
To further confirm the phase purity, the microstructure for the samples with 0.48≤x≤0.58 is characterized by SEM (Fig. 4(a, c-g)), and the mapping on the composition by EDS is carried out on the samples with x=0.48 (Fig. 4(b)) and 0.58 (Fig. 4(h)). No impurity phase can be observed for the samples with 0.5≤x≤0.56. Two types of precipitate are observed in the sample withx=0.48, as shown in Fig. 4(a). The EDS mappings (Fig. 4(b)) show black and white precipitates which are mainly composed of Ag-Se and Bi, respectively. The ratios of Ag:Bi:Se are about 60.1 : 9.3 : 30.6 and 8.9 : 84 : 7.1, respectively, which suggest Ag2Se and Bi impurities. Moreover, Bi2Se3-rich precipitates identified by EDS as well, are observed in the sample 0.58, respectively. Both XRD and SEM results suggest the single phase (Ag2Se)1-x(Bi2Se3)x region of x being 0.5-0.56. Therefore, single phased (Ag2Se)1-x(Bi2Se3)xmaterials with 0.5≤x≤0.56 are focused on.
Fig. 4 SEM images for (Ag2Se)1-x(Bi2Se3)x(0.48≤x≤0.56) (a, c-g) and its corresponding EDS mapping for the samples with x=0.48 (b) and 0.58 (h)
As shown in Fig. 5(a), the Hall carrier concentration (nH) for (Ag2Se)1-x(Bi2Se3)x is found to significantly increase with increasing x. It can be understood by the increase of x would lead to the formation of cation vacancies, which further drives the evaporation of Se due to its high vapor pressure. The deficiency of Se anions would lead to an increase in electron concentration. As a result, an increase in carrier concentration from 1.0×1019 cm-3 to 5.7×1019cm-3 is obtained with increasing x from 0.5 to 0.56. Such a broad carrier concentration range enables a detailed assessment on the electronic transport properties, and a comprehensive understanding of fundamental material parameters. The optical measurements for all the samples are shown in Fig. 5(b). The estimated optical band gap (Eg) is about 0.45 eV, which is in good agreement with literatures (0.5-0.6 eV)[65,71].
Fig. 5 Composition dependent Hall carrier concentration (a) and normalized optical absorption versus photon energy (b) at room temperature for (Ag2Se)1-x(Bi2Se3)x(0.5≤x≤0.56)
Temperature dependent Hall coefficient (RH) and Hall mobility (µH) for (Ag2Se)1-x(Bi2Se3)x are shown in Fig. 6(a). A sharp decrease in µH and RH around 550 K are found, which can reasonably be attributed to the phase transition between rhombohedral and cubic structures. At temperatures apart from phase transition temperature, RH in three phases keeps nearly temperature independent, suggesting a single band transport behavior in a degenerated state. The decrease in μH with increasing temperature via μH~T-1.5, indicates the charge carrier scattering by acoustic phonons.
Fig. 6 Temperature dependent Hall coefficient (RH) and mobility (µH) (a), deformation potential coefficient (Edef) and density of states effective mass (m*) (b), Hall carrier concentration dependent Hall mobility (c) and Seebeck coefficient (d) at different temperatures for (Ag2Se)1-x(Bi2Se3)x(0.5≤x≤0.56), with a comparison to available literature results[52,64-65]. The experimental results here agree well with the model prediction based on a SPB approximation with a dominant scattering by acoustic phonons
According to the above discussion on RH, a single parabolic band model with acoustic phonon scattering is used to understand the transport properties and underlying physical parameters. Assuming a single band valley (band degeneracy of 2), temperature dependent effective deformation potential coefficient (Edef) and density of state effective mass (m*) are shown in Fig. 6(b). It is found that the changes of both carrier concentration and temperature have negligible effects on both Edef and m* for the samples in three phases, indicating a rigid band behavior for (Ag2Se)1-x(Bi2Se3)x. An m* of ~0.51 me and a Edef of ~33 eV are obtained for the samples in the hexagonal structure. The obtained m* is in good agreement with literature[65]. m* and Edef in the rhombohedral phase are about 0.54 me and 29 eV, respectively, while about 4 me and10 eV in the cubic phase.
The Hall carrier concentration dependent Hall mobility, and Seebeck coefficient are shown in Fig. 6(c, d) respectively. Based on estimated average m* and Edef at each temperature (in Fig. 6(b)), the SPB model with the acoustic phonon scattering enables a reasonable prediction on both Seebeck coefficient and Hall mobility at three different temperatures. Moreover, this model prediction agrees well with available literature results[52,64-65].
Temperature dependent Seebeck coefficient and electricalresistivity for (Ag2Se)1-x(Bi2Se3)x are shown in Fig. 7(a, b), respectively. Both Seebeck coefficient and electrical resistivity decrease with increasing x due to the increase of Hall carrier concentration. Moreover, both of them increase with increasing temperature, showing a degenerate semiconducting behavior. Figure 7(a, b) also include the Seebeck coefficient and electrical resistivity for pristine[64] and In-doped[63] AgBiSe2 from literatures for comparison, respectively. It is seen that the lowest Seebeck coefficient and electrical resistivity obtained in this work is comparable to those of In-doped sample. The Seebeck coefficient for all the samples is negative, indicating a n-type conduction, which is consistent with the Hall coefficient measurements (Fig. 6(a)).
Fig. 7 Temperature dependent Seebeck coefficient (a), electrical resistivity (b), total thermal conductivity (c) and lattice thermal conductivity (d) for (Ag2Se)1-x(Bi2Se3)x(0.5≤x≤0.56), with a comparison to available literature results[63,64]
Figure 7(c, d) show the temperature dependent total thermal conductivity (κ) and lattice thermal conductivity (κL) for (Ag2Se)1-x(Bi2Se3)x, respectively. κL is obtained by subtracting the electronic thermal conductivity (κE) from the total thermal conductivity via the Wiedemann-Franz Law, κE=LT/ρ, where L is the Lorenz factor determined by the SPB model with the acoustic phonon scattering. Both κ and κL decrease with increasing temperature. The κ slightly increase with increasing x due to the increased carrier concentration leading to higher κE. It is seen that the κL is lower than 0.7 W/(m·K) in the entire temperature range, mainly resulting from the strong anharmonicity[42,46,72] and strong phonon scattering by disorded cations[42,61,72]. The κL at high temperatures in the cubic phase is found to be as low as~0.4 W/(m·K), showing great potential for thermoelectric applications.
The sound velocities (vs) of longitudinal (vL) and transverse (vT) branches, as the important parameters determining kL, are measured and listed in Table 1. Moreover, the physical parameters including Debye temperature (qD), bulk modulus (B) and Grüeneisen parameter (g) are estimated based on the measured vL and vT[73,74], as listed in Table 1. It is shown that the change in sound velocities for all the samples does not exceed 5%, which is within the measurement uncertainty range. This excludes the influence of lattice softening on kL. This material shows a very low sound velocity of ~1500 m/s, one of the lowest sound velocities among thermoelectrics[39,75]. Moreover, the Grüneisen parameter (γ) as large as 2 indicates the strong anharmonicity[46]. Both the low sound velocity and the strong lattice anharmonicity could be the origin for the low κL observed.
Table 1
Table 1 Measured sound velocities and the estimated physical parameters for (Ag2Se)1-x(Bi2Se3)x(0.5≤x≤0.56)
Temperature dependent figure of merit (ZT) for (Ag2Se)1-x(Bi2Se3)x is shown in Fig. 8(a). ZTs for all the samples increase with increasing temperature and x, due to the carrier concentration optimization. Thus, a peak ZT of 0.5 at 700 K is achieved for the sample with the highest carrier concentration. The SPB model further enables a prediction in carrier concentration dependent ZT at different temperatures using the experimental kL (Fig. 8(b)). The predicted ZT agrees well with the experimental data as shown in Fig. 8(b). It is found the highest carrier concentration obtained in this work is very close to the optimal one. According to the calculated band structure[71], engineering the band should enable a possibility for further enhancing the thermoelectric performance.
Fig. 8 Temperature dependent ZT for (Ag2Se)1-x(Bi2Se3)x(0.5≤x≤0.56) (a) and Hall carrier concentration dependentZT at different temperatures (b) with a comparison to model prediction and literature results[52,63-65]
3 Conclusion
In this work, a composition control for (Ag2Se)1-x(Bi2Se3)xwith x in the range of 0.5-0.56 enables the carrier concentration ranging in (1.0-5.7)×1019cm-3, which allows a systematical understanding on the fundamental physical parameters determining its transport properties. It is shown that the electronic transport properties can be well understood by a single parabolic band model. The carrier concentration is well optimized in this work, leading to a peak ZT of 0.5 with the help of intrinsically low lattice thermal conductivity. This work offers a fundamental understanding on the material physics affecting the thermoelectric performance, which could guide the further improvements for this material.
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1
2017
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Realizing zT of 2.3 in Ge1-x-ySbxInyTe via reducing the phase-transition temperature and introducing resonant energy doping
1
2018
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Optimizing the thermoelectric performance of low-temperature SnSe compounds by electronic structure design
1
2015
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Convergence of conduction bands as a means of enhancing thermoelectric performance of n-type Mg2Si1-xSnx solid solutions
1
2012
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Realizing high figure of merit in heavy-band p-type half-Heusler thermoelectric materials
1
2015
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Manipulation of phonon transport in thermoelectrics
1
2018
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Nanostructured thermoelectrics: the new paradigm?
1
2010
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
High thermoelectric performance in PbTe due to large nanoscale Ag2Te precipitates and La doping
1
2011
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
High ZT in nanostructuring AgSbTe2
2
2010
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
... Ternary chalcogenides I-V-VI2 compounds (where I=Cu, Ag or alkali metal; V=Sb, Bi; and VI=S, Se, Te) have aroused widespread interests for thermoelectric applications due to their intrinsically low kL stemming from the strong anharmonicity induced by lone s2 pair electrons of the group V cations[46]. So far, the study of their thermoelectric properties mainly focuses on the Ag-based compounds, particularly Ag(Sb/Bi)(Te/Se)2[23,47-55]. The peak ZTs of 2.0 and 1.2 for AgSbTe2 and AgSbSe2 have been realized through band engineering and carrier concentration optimization[48,56], respectively, which are considered as potentially lead-free alternatives for p-type PbTe. ...
Improving the zT value of thermoelectrics by nanostructuring: tuning the nanoparticle morphology of Sb2Te3 by using ionic liquids
1
2017
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Nanostructured thermoelectrics
1
2010
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Enhanced thermoelectric performance of beta-Zn4Sb3 based nanocomposites through combined effects of density of states resonance and carrier energy filtering
1
2015
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
High-thermoelectric performance of nanostructured bismuth antimony telluride bulk alloys
1
2008
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
BixSb2-xTe3 nanoplates with enhanced thermoelectric performance due to sufficiently decoupled electronic transport properties and strong wide-frequency phonon scatterings
1
2016
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
n-type Bi2Te3-xSexnanoplates with enhanced thermoelectric efficiency driven by wide-frequency phonon scatterings and synergistic carrier scatterings
1
2016
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Thermoelectric properties of Cu2SnSe4 with intrinsic vacancy
1
2016
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Point defect engineering of high-performance bismuth-telluride-based thermoelectric materials
1
2014
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Interstitial point defect scattering contributing to high thermoelectric performance in SnTe
1
2016
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Influence of cation-vacancy defects on the properties of CuInSe2-ZnIn2Se4 solid solutions
1
2015
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Thermoelectrics dense dislocation arrays embedded in grain boundaries for high-performance bulk thermoelectrics
1
2015
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Vacancy-induced dislocations within grains for high-performance PbSe thermoelectrics
1
2017
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Copper ion liquid-like thermoelectrics
1
2012
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Part-crystalline part-liquid state and rattling-like thermal damping in materials with chemical-bond hierarchy
1
2014
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Low sound velocity contributing to the high thermoelectric performance of Ag8SnSe6
2
2016
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
... The sound velocities (vs) of longitudinal (vL) and transverse (vT) branches, as the important parameters determining kL, are measured and listed in Table 1. Moreover, the physical parameters including Debye temperature (qD), bulk modulus (B) and Grüeneisen parameter (g) are estimated based on the measured vL and vT[73,74], as listed in Table 1. It is shown that the change in sound velocities for all the samples does not exceed 5%, which is within the measurement uncertainty range. This excludes the influence of lattice softening on kL. This material shows a very low sound velocity of ~1500 m/s, one of the lowest sound velocities among thermoelectrics[39,75]. Moreover, the Grüneisen parameter (γ) as large as 2 indicates the strong anharmonicity[46]. Both the low sound velocity and the strong lattice anharmonicity could be the origin for the low κL observed. ...
Promising thermoelectric Ag5-δTe3 with intrinsic low lattice thermal conductivity
1
2017
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Crystal structure induced ultralow lattice thermal conductivity in thermoelectric Ag9AlSe6
1
2018
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Intrinsically minimal thermal conductivity in cubic I-V-VI2 semiconductors
3
2008
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
... Figure 7(c, d) show the temperature dependent total thermal conductivity (κ) and lattice thermal conductivity (κL) for (Ag2Se)1-x(Bi2Se3)x, respectively. κL is obtained by subtracting the electronic thermal conductivity (κE) from the total thermal conductivity via the Wiedemann-Franz Law, κE=LT/ρ, where L is the Lorenz factor determined by the SPB model with the acoustic phonon scattering. Both κ and κL decrease with increasing temperature. The κ slightly increase with increasing x due to the increased carrier concentration leading to higher κE. It is seen that the κL is lower than 0.7 W/(m·K) in the entire temperature range, mainly resulting from the strong anharmonicity[42,46,72] and strong phonon scattering by disorded cations[42,61,72]. The κL at high temperatures in the cubic phase is found to be as low as~0.4 W/(m·K), showing great potential for thermoelectric applications. ...
... [42,61,72]. The κL at high temperatures in the cubic phase is found to be as low as~0.4 W/(m·K), showing great potential for thermoelectric applications. ...
Nanostructuring, carrier engineering and bond anharmonicity synergistically boost the thermoelectric performance of p-type AgSbSe2-ZnSe
1
2014
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
Predicting high thermoelectric performance of ABX ternary compounds NaMgX (X = P, Sb, As) with weak electron-phonon coupling and strong bonding anharmonicity
1
2016
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
High thermoelectric performance of Ag9GaSe6 enabled by low cutoff frequency of acoustic phonons
1
2017
... However, the strong coupling among S,ρandkEvia the carrier concentration, band structure and charge scattering, results in a simultaneous optimization of these parameters to be difficult[7,8]. The newly developed strategy of band engineering[9,10] successfully decouples the correlation, leading to a significant enhancement in power factor (S2/ρ) and then an increased ZT in various materials, such as PbTe[11], SnTe[12,13], GeTe[14,15,16], SnSe[17], Mg2Si[18]and half-Heusler[19]. Alternatively, minimizing kL[20], the only independent parameter determining ZT, through nanostructuring[21,22,23,24,25,26,27,28,29], point defects[30,31,32,33,34], dislocations[11,35-36], liquid phonons[37,38], low sound velocity[39,40,41], lattice anharmonicity[42,43,44], and low cutoff frequency of acoustic phonons[45], has effectively resulted in a ZT-enhancement as well. ...
... Ternary chalcogenides I-V-VI2 compounds (where I=Cu, Ag or alkali metal; V=Sb, Bi; and VI=S, Se, Te) have aroused widespread interests for thermoelectric applications due to their intrinsically low kL stemming from the strong anharmonicity induced by lone s2 pair electrons of the group V cations[46]. So far, the study of their thermoelectric properties mainly focuses on the Ag-based compounds, particularly Ag(Sb/Bi)(Te/Se)2[23,47-55]. The peak ZTs of 2.0 and 1.2 for AgSbTe2 and AgSbSe2 have been realized through band engineering and carrier concentration optimization[48,56], respectively, which are considered as potentially lead-free alternatives for p-type PbTe. ...
... Figure 7(c, d) show the temperature dependent total thermal conductivity (κ) and lattice thermal conductivity (κL) for (Ag2Se)1-x(Bi2Se3)x, respectively. κL is obtained by subtracting the electronic thermal conductivity (κE) from the total thermal conductivity via the Wiedemann-Franz Law, κE=LT/ρ, where L is the Lorenz factor determined by the SPB model with the acoustic phonon scattering. Both κ and κL decrease with increasing temperature. The κ slightly increase with increasing x due to the increased carrier concentration leading to higher κE. It is seen that the κL is lower than 0.7 W/(m·K) in the entire temperature range, mainly resulting from the strong anharmonicity[42,46,72] and strong phonon scattering by disorded cations[42,61,72]. The κL at high temperatures in the cubic phase is found to be as low as~0.4 W/(m·K), showing great potential for thermoelectric applications. ...
... The sound velocities (vs) of longitudinal (vL) and transverse (vT) branches, as the important parameters determining kL, are measured and listed in Table 1. Moreover, the physical parameters including Debye temperature (qD), bulk modulus (B) and Grüeneisen parameter (g) are estimated based on the measured vL and vT[73,74], as listed in Table 1. It is shown that the change in sound velocities for all the samples does not exceed 5%, which is within the measurement uncertainty range. This excludes the influence of lattice softening on kL. This material shows a very low sound velocity of ~1500 m/s, one of the lowest sound velocities among thermoelectrics[39,75]. Moreover, the Grüneisen parameter (γ) as large as 2 indicates the strong anharmonicity[46]. Both the low sound velocity and the strong lattice anharmonicity could be the origin for the low κL observed. ...
Glass-like phonon scattering from a spontaneous nanostructure in AgSbTe2. Nat
1
2013
... Ternary chalcogenides I-V-VI2 compounds (where I=Cu, Ag or alkali metal; V=Sb, Bi; and VI=S, Se, Te) have aroused widespread interests for thermoelectric applications due to their intrinsically low kL stemming from the strong anharmonicity induced by lone s2 pair electrons of the group V cations[46]. So far, the study of their thermoelectric properties mainly focuses on the Ag-based compounds, particularly Ag(Sb/Bi)(Te/Se)2[23,47-55]. The peak ZTs of 2.0 and 1.2 for AgSbTe2 and AgSbSe2 have been realized through band engineering and carrier concentration optimization[48,56], respectively, which are considered as potentially lead-free alternatives for p-type PbTe. ...
High thermoelectric properties for Sn-doped AgSbSe2
1
2015
... Ternary chalcogenides I-V-VI2 compounds (where I=Cu, Ag or alkali metal; V=Sb, Bi; and VI=S, Se, Te) have aroused widespread interests for thermoelectric applications due to their intrinsically low kL stemming from the strong anharmonicity induced by lone s2 pair electrons of the group V cations[46]. So far, the study of their thermoelectric properties mainly focuses on the Ag-based compounds, particularly Ag(Sb/Bi)(Te/Se)2[23,47-55]. The peak ZTs of 2.0 and 1.2 for AgSbTe2 and AgSbSe2 have been realized through band engineering and carrier concentration optimization[48,56], respectively, which are considered as potentially lead-free alternatives for p-type PbTe. ...
High thermoelectric performance in tellurium free p-type AgSbSe2
2013
Enhanced thermoelectric performance in p-type AgSbSe2 by Cd-doping
2014
Enhancement of thermoelectric properties by Na doping in Te-free p-type AgSbSe2
2015
High thermoelectric properties of n-type AgBiSe2.
4
2013
... As one of a few n-type semiconductors among this family of compounds, the crystal structure of AgBiSe2 transforms from hexagonal to rhombohedral and then to cubic with increasing temperature[57,58,59,60], as shown in Fig. 1(a). The cubic AgBiSe2 shows highly disorder at cation sites, which are beneficial for the low kL through the strong phonon scattering by point defects[61]. Recently, numerous efforts have been put on its thermoelectric performance. In order to enhance the power factor (S2/ρ), Nb-[52], Ge-[62], In-doping[63] at cation site or Te-[64], Cl-doping[65] at anion site are carried out, and an enhanced ZT up to 0.7 is obtained in single phase AgBiSe2 at 773 K. It is well known that a realization in the highest possible ZT, even using the successful strategies mentioned above, strongly depends on an optimization in carrier concentration[66,67,68]. Therefore, an investigation on the transport properties in a broad carrier concentration range, is essential to fully assess the potential for thermoelectric applications. ...
... Temperature dependent Hall coefficient (RH) and mobility (µH) (a), deformation potential coefficient (Edef) and density of states effective mass (m*) (b), Hall carrier concentration dependent Hall mobility (c) and Seebeck coefficient (d) at different temperatures for (Ag2Se)1-x(Bi2Se3)x(0.5≤x≤0.56), with a comparison to available literature results[52,64-65]. The experimental results here agree well with the model prediction based on a SPB approximation with a dominant scattering by acoustic phonons ...
... The Hall carrier concentration dependent Hall mobility, and Seebeck coefficient are shown in Fig. 6(c, d) respectively. Based on estimated average m* and Edef at each temperature (in Fig. 6(b)), the SPB model with the acoustic phonon scattering enables a reasonable prediction on both Seebeck coefficient and Hall mobility at three different temperatures. Moreover, this model prediction agrees well with available literature results[52,64-65]. ...
... Temperature dependent ZT for (Ag2Se)1-x(Bi2Se3)x(0.5≤x≤0.56) (a) and Hall carrier concentration dependentZT at different temperatures (b) with a comparison to model prediction and literature results[52,63-65] ...
Comparing the role of annealing on the transport properties of polymorphous AgBiSe2 and monophase AgSbSe2
2018
High thermoelectric and reversible p-n-p conduction type switching integrated in dimetal chalcogenide.
2012
Extraordinary thermoelectric performance realized in hierarchically structured AgSbSe2 with ultralow thermal conductivity. ACS Appl. Mater
1
2018
... Ternary chalcogenides I-V-VI2 compounds (where I=Cu, Ag or alkali metal; V=Sb, Bi; and VI=S, Se, Te) have aroused widespread interests for thermoelectric applications due to their intrinsically low kL stemming from the strong anharmonicity induced by lone s2 pair electrons of the group V cations[46]. So far, the study of their thermoelectric properties mainly focuses on the Ag-based compounds, particularly Ag(Sb/Bi)(Te/Se)2[23,47-55]. The peak ZTs of 2.0 and 1.2 for AgSbTe2 and AgSbSe2 have been realized through band engineering and carrier concentration optimization[48,56], respectively, which are considered as potentially lead-free alternatives for p-type PbTe. ...
Achieving ZT>2 in p-type AgSbTe2-xSexalloys via exploring the extra light valence band and introducing dense stacking faults
1
2018
... Ternary chalcogenides I-V-VI2 compounds (where I=Cu, Ag or alkali metal; V=Sb, Bi; and VI=S, Se, Te) have aroused widespread interests for thermoelectric applications due to their intrinsically low kL stemming from the strong anharmonicity induced by lone s2 pair electrons of the group V cations[46]. So far, the study of their thermoelectric properties mainly focuses on the Ag-based compounds, particularly Ag(Sb/Bi)(Te/Se)2[23,47-55]. The peak ZTs of 2.0 and 1.2 for AgSbTe2 and AgSbSe2 have been realized through band engineering and carrier concentration optimization[48,56], respectively, which are considered as potentially lead-free alternatives for p-type PbTe. ...
Phase diagrams of the pseudo-binary Cu2Se-Bi2Se3 and Ag2Se-Bi2Se3 systems and thermoelectric properties of Cu2Se-Bi2Se3 solid solution
3
1966
... As one of a few n-type semiconductors among this family of compounds, the crystal structure of AgBiSe2 transforms from hexagonal to rhombohedral and then to cubic with increasing temperature[57,58,59,60], as shown in Fig. 1(a). The cubic AgBiSe2 shows highly disorder at cation sites, which are beneficial for the low kL through the strong phonon scattering by point defects[61]. Recently, numerous efforts have been put on its thermoelectric performance. In order to enhance the power factor (S2/ρ), Nb-[52], Ge-[62], In-doping[63] at cation site or Te-[64], Cl-doping[65] at anion site are carried out, and an enhanced ZT up to 0.7 is obtained in single phase AgBiSe2 at 773 K. It is well known that a realization in the highest possible ZT, even using the successful strategies mentioned above, strongly depends on an optimization in carrier concentration[66,67,68]. Therefore, an investigation on the transport properties in a broad carrier concentration range, is essential to fully assess the potential for thermoelectric applications. ...
... Crystal structures for the different phases of AgBiSe2 (a) and phase diagram of Ag2Se-Bi2Se3 system (b)[57] ...
... According to the phase diagram of Ag2Se-Bi2Se3 system[57] (Fig. 1(b)), (Ag2Se)1-x(Bi2Se3)x shows a single phase region at x ranging from 0.4 to 0.62. This tunable composition in a broad range suggests an availability of carrier concentration tuning for thermoelectric (Ag2Se)1-x(Bi2Se3)x. Powder XRD patterns for (Ag2Se)1-x(Bi2Se3)x(0.4≤x≤0.62) are shown in Fig. 2. It is found that the single phase region confines x to be from 0.48 to 0.56, since Ag2Se and Bi2Se3 impurity phases are observed for the samples with x≤0.46 andx≥0.58, respectively. As shown in Fig. 3(a), the locally enlarged XRDpatterns for the samples with single phase (0.48≤x≤0.56) show that the diffraction peaks shift to higher angles with increasing x. The dependence of lattice parameters on x in Fig. 3(b) shows that both a and c decrease with increasing x, which can be understood by the introduction of cation vacancy as x>0.5. ...
Constitution of the AgSbSe2-AgSbTe2-AgBiSe2-AgBiTe2 system
1
1958
... As one of a few n-type semiconductors among this family of compounds, the crystal structure of AgBiSe2 transforms from hexagonal to rhombohedral and then to cubic with increasing temperature[57,58,59,60], as shown in Fig. 1(a). The cubic AgBiSe2 shows highly disorder at cation sites, which are beneficial for the low kL through the strong phonon scattering by point defects[61]. Recently, numerous efforts have been put on its thermoelectric performance. In order to enhance the power factor (S2/ρ), Nb-[52], Ge-[62], In-doping[63] at cation site or Te-[64], Cl-doping[65] at anion site are carried out, and an enhanced ZT up to 0.7 is obtained in single phase AgBiSe2 at 773 K. It is well known that a realization in the highest possible ZT, even using the successful strategies mentioned above, strongly depends on an optimization in carrier concentration[66,67,68]. Therefore, an investigation on the transport properties in a broad carrier concentration range, is essential to fully assess the potential for thermoelectric applications. ...
Electron microscopic study of polymorphismand defects in AgBiSe2 and AgBiS2
1
1977
... As one of a few n-type semiconductors among this family of compounds, the crystal structure of AgBiSe2 transforms from hexagonal to rhombohedral and then to cubic with increasing temperature[57,58,59,60], as shown in Fig. 1(a). The cubic AgBiSe2 shows highly disorder at cation sites, which are beneficial for the low kL through the strong phonon scattering by point defects[61]. Recently, numerous efforts have been put on its thermoelectric performance. In order to enhance the power factor (S2/ρ), Nb-[52], Ge-[62], In-doping[63] at cation site or Te-[64], Cl-doping[65] at anion site are carried out, and an enhanced ZT up to 0.7 is obtained in single phase AgBiSe2 at 773 K. It is well known that a realization in the highest possible ZT, even using the successful strategies mentioned above, strongly depends on an optimization in carrier concentration[66,67,68]. Therefore, an investigation on the transport properties in a broad carrier concentration range, is essential to fully assess the potential for thermoelectric applications. ...
Ternary semiconducting compounds with sodium chloride-like structure-AgSbSe2, AgSbTe2, AgBiS2, AgBiSe2
1
2001
... As one of a few n-type semiconductors among this family of compounds, the crystal structure of AgBiSe2 transforms from hexagonal to rhombohedral and then to cubic with increasing temperature[57,58,59,60], as shown in Fig. 1(a). The cubic AgBiSe2 shows highly disorder at cation sites, which are beneficial for the low kL through the strong phonon scattering by point defects[61]. Recently, numerous efforts have been put on its thermoelectric performance. In order to enhance the power factor (S2/ρ), Nb-[52], Ge-[62], In-doping[63] at cation site or Te-[64], Cl-doping[65] at anion site are carried out, and an enhanced ZT up to 0.7 is obtained in single phase AgBiSe2 at 773 K. It is well known that a realization in the highest possible ZT, even using the successful strategies mentioned above, strongly depends on an optimization in carrier concentration[66,67,68]. Therefore, an investigation on the transport properties in a broad carrier concentration range, is essential to fully assess the potential for thermoelectric applications. ...
Atomic and electronic structures of I-V-VI2 ternary chalcogenides
2
2016
... As one of a few n-type semiconductors among this family of compounds, the crystal structure of AgBiSe2 transforms from hexagonal to rhombohedral and then to cubic with increasing temperature[57,58,59,60], as shown in Fig. 1(a). The cubic AgBiSe2 shows highly disorder at cation sites, which are beneficial for the low kL through the strong phonon scattering by point defects[61]. Recently, numerous efforts have been put on its thermoelectric performance. In order to enhance the power factor (S2/ρ), Nb-[52], Ge-[62], In-doping[63] at cation site or Te-[64], Cl-doping[65] at anion site are carried out, and an enhanced ZT up to 0.7 is obtained in single phase AgBiSe2 at 773 K. It is well known that a realization in the highest possible ZT, even using the successful strategies mentioned above, strongly depends on an optimization in carrier concentration[66,67,68]. Therefore, an investigation on the transport properties in a broad carrier concentration range, is essential to fully assess the potential for thermoelectric applications. ...
... Figure 7(c, d) show the temperature dependent total thermal conductivity (κ) and lattice thermal conductivity (κL) for (Ag2Se)1-x(Bi2Se3)x, respectively. κL is obtained by subtracting the electronic thermal conductivity (κE) from the total thermal conductivity via the Wiedemann-Franz Law, κE=LT/ρ, where L is the Lorenz factor determined by the SPB model with the acoustic phonon scattering. Both κ and κL decrease with increasing temperature. The κ slightly increase with increasing x due to the increased carrier concentration leading to higher κE. It is seen that the κL is lower than 0.7 W/(m·K) in the entire temperature range, mainly resulting from the strong anharmonicity[42,46,72] and strong phonon scattering by disorded cations[42,61,72]. The κL at high temperatures in the cubic phase is found to be as low as~0.4 W/(m·K), showing great potential for thermoelectric applications. ...
Ultralow thermal conductivity in n-type Ge-doped AgBiSe2 thermoelectric materials
1
2017
... As one of a few n-type semiconductors among this family of compounds, the crystal structure of AgBiSe2 transforms from hexagonal to rhombohedral and then to cubic with increasing temperature[57,58,59,60], as shown in Fig. 1(a). The cubic AgBiSe2 shows highly disorder at cation sites, which are beneficial for the low kL through the strong phonon scattering by point defects[61]. Recently, numerous efforts have been put on its thermoelectric performance. In order to enhance the power factor (S2/ρ), Nb-[52], Ge-[62], In-doping[63] at cation site or Te-[64], Cl-doping[65] at anion site are carried out, and an enhanced ZT up to 0.7 is obtained in single phase AgBiSe2 at 773 K. It is well known that a realization in the highest possible ZT, even using the successful strategies mentioned above, strongly depends on an optimization in carrier concentration[66,67,68]. Therefore, an investigation on the transport properties in a broad carrier concentration range, is essential to fully assess the potential for thermoelectric applications. ...
4
2016
... As one of a few n-type semiconductors among this family of compounds, the crystal structure of AgBiSe2 transforms from hexagonal to rhombohedral and then to cubic with increasing temperature[57,58,59,60], as shown in Fig. 1(a). The cubic AgBiSe2 shows highly disorder at cation sites, which are beneficial for the low kL through the strong phonon scattering by point defects[61]. Recently, numerous efforts have been put on its thermoelectric performance. In order to enhance the power factor (S2/ρ), Nb-[52], Ge-[62], In-doping[63] at cation site or Te-[64], Cl-doping[65] at anion site are carried out, and an enhanced ZT up to 0.7 is obtained in single phase AgBiSe2 at 773 K. It is well known that a realization in the highest possible ZT, even using the successful strategies mentioned above, strongly depends on an optimization in carrier concentration[66,67,68]. Therefore, an investigation on the transport properties in a broad carrier concentration range, is essential to fully assess the potential for thermoelectric applications. ...
... Temperature dependent Seebeck coefficient and electricalresistivity for (Ag2Se)1-x(Bi2Se3)x are shown in Fig. 7(a, b), respectively. Both Seebeck coefficient and electrical resistivity decrease with increasing x due to the increase of Hall carrier concentration. Moreover, both of them increase with increasing temperature, showing a degenerate semiconducting behavior. Figure 7(a, b) also include the Seebeck coefficient and electrical resistivity for pristine[64] and In-doped[63] AgBiSe2 from literatures for comparison, respectively. It is seen that the lowest Seebeck coefficient and electrical resistivity obtained in this work is comparable to those of In-doped sample. The Seebeck coefficient for all the samples is negative, indicating a n-type conduction, which is consistent with the Hall coefficient measurements (Fig. 6(a)). ...
... Temperature dependent Seebeck coefficient (a), electrical resistivity (b), total thermal conductivity (c) and lattice thermal conductivity (d) for (Ag2Se)1-x(Bi2Se3)x(0.5≤x≤0.56), with a comparison to available literature results[63,64] ...
... Temperature dependent ZT for (Ag2Se)1-x(Bi2Se3)x(0.5≤x≤0.56) (a) and Hall carrier concentration dependentZT at different temperatures (b) with a comparison to model prediction and literature results[52,63-65] ...
Effect of Te substitution on crystal structure and transport properties of AgBiSe2 thermoelectric material
5
2018
... As one of a few n-type semiconductors among this family of compounds, the crystal structure of AgBiSe2 transforms from hexagonal to rhombohedral and then to cubic with increasing temperature[57,58,59,60], as shown in Fig. 1(a). The cubic AgBiSe2 shows highly disorder at cation sites, which are beneficial for the low kL through the strong phonon scattering by point defects[61]. Recently, numerous efforts have been put on its thermoelectric performance. In order to enhance the power factor (S2/ρ), Nb-[52], Ge-[62], In-doping[63] at cation site or Te-[64], Cl-doping[65] at anion site are carried out, and an enhanced ZT up to 0.7 is obtained in single phase AgBiSe2 at 773 K. It is well known that a realization in the highest possible ZT, even using the successful strategies mentioned above, strongly depends on an optimization in carrier concentration[66,67,68]. Therefore, an investigation on the transport properties in a broad carrier concentration range, is essential to fully assess the potential for thermoelectric applications. ...
... Temperature dependent Hall coefficient (RH) and mobility (µH) (a), deformation potential coefficient (Edef) and density of states effective mass (m*) (b), Hall carrier concentration dependent Hall mobility (c) and Seebeck coefficient (d) at different temperatures for (Ag2Se)1-x(Bi2Se3)x(0.5≤x≤0.56), with a comparison to available literature results[52,64-65]. The experimental results here agree well with the model prediction based on a SPB approximation with a dominant scattering by acoustic phonons ...
... The Hall carrier concentration dependent Hall mobility, and Seebeck coefficient are shown in Fig. 6(c, d) respectively. Based on estimated average m* and Edef at each temperature (in Fig. 6(b)), the SPB model with the acoustic phonon scattering enables a reasonable prediction on both Seebeck coefficient and Hall mobility at three different temperatures. Moreover, this model prediction agrees well with available literature results[52,64-65]. ...
... Temperature dependent Seebeck coefficient and electricalresistivity for (Ag2Se)1-x(Bi2Se3)x are shown in Fig. 7(a, b), respectively. Both Seebeck coefficient and electrical resistivity decrease with increasing x due to the increase of Hall carrier concentration. Moreover, both of them increase with increasing temperature, showing a degenerate semiconducting behavior. Figure 7(a, b) also include the Seebeck coefficient and electrical resistivity for pristine[64] and In-doped[63] AgBiSe2 from literatures for comparison, respectively. It is seen that the lowest Seebeck coefficient and electrical resistivity obtained in this work is comparable to those of In-doped sample. The Seebeck coefficient for all the samples is negative, indicating a n-type conduction, which is consistent with the Hall coefficient measurements (Fig. 6(a)). ...
... Temperature dependent Seebeck coefficient (a), electrical resistivity (b), total thermal conductivity (c) and lattice thermal conductivity (d) for (Ag2Se)1-x(Bi2Se3)x(0.5≤x≤0.56), with a comparison to available literature results[63,64] ...
Promising thermoelectric performance in n-type AgBiSe2: effect of aliovalent anion doping
5
2015
... As one of a few n-type semiconductors among this family of compounds, the crystal structure of AgBiSe2 transforms from hexagonal to rhombohedral and then to cubic with increasing temperature[57,58,59,60], as shown in Fig. 1(a). The cubic AgBiSe2 shows highly disorder at cation sites, which are beneficial for the low kL through the strong phonon scattering by point defects[61]. Recently, numerous efforts have been put on its thermoelectric performance. In order to enhance the power factor (S2/ρ), Nb-[52], Ge-[62], In-doping[63] at cation site or Te-[64], Cl-doping[65] at anion site are carried out, and an enhanced ZT up to 0.7 is obtained in single phase AgBiSe2 at 773 K. It is well known that a realization in the highest possible ZT, even using the successful strategies mentioned above, strongly depends on an optimization in carrier concentration[66,67,68]. Therefore, an investigation on the transport properties in a broad carrier concentration range, is essential to fully assess the potential for thermoelectric applications. ...
... As shown in Fig. 5(a), the Hall carrier concentration (nH) for (Ag2Se)1-x(Bi2Se3)x is found to significantly increase with increasing x. It can be understood by the increase of x would lead to the formation of cation vacancies, which further drives the evaporation of Se due to its high vapor pressure. The deficiency of Se anions would lead to an increase in electron concentration. As a result, an increase in carrier concentration from 1.0×1019 cm-3 to 5.7×1019cm-3 is obtained with increasing x from 0.5 to 0.56. Such a broad carrier concentration range enables a detailed assessment on the electronic transport properties, and a comprehensive understanding of fundamental material parameters. The optical measurements for all the samples are shown in Fig. 5(b). The estimated optical band gap (Eg) is about 0.45 eV, which is in good agreement with literatures (0.5-0.6 eV)[65,71]. ...
... Temperature dependent Hall coefficient (RH) and mobility (µH) (a), deformation potential coefficient (Edef) and density of states effective mass (m*) (b), Hall carrier concentration dependent Hall mobility (c) and Seebeck coefficient (d) at different temperatures for (Ag2Se)1-x(Bi2Se3)x(0.5≤x≤0.56), with a comparison to available literature results[52,64-65]. The experimental results here agree well with the model prediction based on a SPB approximation with a dominant scattering by acoustic phonons ...
... The Hall carrier concentration dependent Hall mobility, and Seebeck coefficient are shown in Fig. 6(c, d) respectively. Based on estimated average m* and Edef at each temperature (in Fig. 6(b)), the SPB model with the acoustic phonon scattering enables a reasonable prediction on both Seebeck coefficient and Hall mobility at three different temperatures. Moreover, this model prediction agrees well with available literature results[52,64-65]. ...
... Temperature dependent ZT for (Ag2Se)1-x(Bi2Se3)x(0.5≤x≤0.56) (a) and Hall carrier concentration dependentZT at different temperatures (b) with a comparison to model prediction and literature results[52,63-65] ...
1
1995
... As one of a few n-type semiconductors among this family of compounds, the crystal structure of AgBiSe2 transforms from hexagonal to rhombohedral and then to cubic with increasing temperature[57,58,59,60], as shown in Fig. 1(a). The cubic AgBiSe2 shows highly disorder at cation sites, which are beneficial for the low kL through the strong phonon scattering by point defects[61]. Recently, numerous efforts have been put on its thermoelectric performance. In order to enhance the power factor (S2/ρ), Nb-[52], Ge-[62], In-doping[63] at cation site or Te-[64], Cl-doping[65] at anion site are carried out, and an enhanced ZT up to 0.7 is obtained in single phase AgBiSe2 at 773 K. It is well known that a realization in the highest possible ZT, even using the successful strategies mentioned above, strongly depends on an optimization in carrier concentration[66,67,68]. Therefore, an investigation on the transport properties in a broad carrier concentration range, is essential to fully assess the potential for thermoelectric applications. ...
Optimum carrier concentration in n-type PbTe thermoelectrics
1
2014
... As one of a few n-type semiconductors among this family of compounds, the crystal structure of AgBiSe2 transforms from hexagonal to rhombohedral and then to cubic with increasing temperature[57,58,59,60], as shown in Fig. 1(a). The cubic AgBiSe2 shows highly disorder at cation sites, which are beneficial for the low kL through the strong phonon scattering by point defects[61]. Recently, numerous efforts have been put on its thermoelectric performance. In order to enhance the power factor (S2/ρ), Nb-[52], Ge-[62], In-doping[63] at cation site or Te-[64], Cl-doping[65] at anion site are carried out, and an enhanced ZT up to 0.7 is obtained in single phase AgBiSe2 at 773 K. It is well known that a realization in the highest possible ZT, even using the successful strategies mentioned above, strongly depends on an optimization in carrier concentration[66,67,68]. Therefore, an investigation on the transport properties in a broad carrier concentration range, is essential to fully assess the potential for thermoelectric applications. ...
Manipulation of charge transport in thermoelectrics
1
2017
... As one of a few n-type semiconductors among this family of compounds, the crystal structure of AgBiSe2 transforms from hexagonal to rhombohedral and then to cubic with increasing temperature[57,58,59,60], as shown in Fig. 1(a). The cubic AgBiSe2 shows highly disorder at cation sites, which are beneficial for the low kL through the strong phonon scattering by point defects[61]. Recently, numerous efforts have been put on its thermoelectric performance. In order to enhance the power factor (S2/ρ), Nb-[52], Ge-[62], In-doping[63] at cation site or Te-[64], Cl-doping[65] at anion site are carried out, and an enhanced ZT up to 0.7 is obtained in single phase AgBiSe2 at 773 K. It is well known that a realization in the highest possible ZT, even using the successful strategies mentioned above, strongly depends on an optimization in carrier concentration[66,67,68]. Therefore, an investigation on the transport properties in a broad carrier concentration range, is essential to fully assess the potential for thermoelectric applications. ...
Band and scattering tuning for high performance thermoelectric Sn1-xMnxTe alloys
1
2015
... The details of the electronic transports (Seebeck coefficient, electronic resistivity and Hall coefficient) measurements are given in the literature[69]. The thermal conductivity was estimated viaκ = dCpD, where d is the geometric density, Cp is the heat capacity, and D is the thermal diffusivity. Parameter D was measured using a laser flash technique with the Netzsch LFA457 system, and Cp was determined by the Dulong-Petit limit and assumed to be temperature independent. All the transport property measurements were carried out under helium atmosphere from 300 K to 700 K. The measurement uncertainty for each transport property (S, ρand κ) is about 5%. ...
Optical band gap and the Burstein-Moss effect in iodine doped PbTe using diffuse reflectance infrared Fourier transform spectroscopy
1
2013
... Phase composition and microstructures were identified by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM, Phenom Pro) equipped with an Energy Dispersive spectrometer. The longitudinal (vL) and transverse (vT) sound velocities were measured on the pellet samples at room temperature using an ultrasonic pulse receiver (Olympus-NDT) equipped with an oscilloscope (Keysight). Infrared Fourier transform spectroscopy (Bruker Tensor 2) was used to measure the optical reflectance coefficient for estimating the optical band gap[70]. ...
Benefits of carrier-pocket anisotropy to thermoelectric performance: the case of p-type AgBiSe2
2
2015
... As shown in Fig. 5(a), the Hall carrier concentration (nH) for (Ag2Se)1-x(Bi2Se3)x is found to significantly increase with increasing x. It can be understood by the increase of x would lead to the formation of cation vacancies, which further drives the evaporation of Se due to its high vapor pressure. The deficiency of Se anions would lead to an increase in electron concentration. As a result, an increase in carrier concentration from 1.0×1019 cm-3 to 5.7×1019cm-3 is obtained with increasing x from 0.5 to 0.56. Such a broad carrier concentration range enables a detailed assessment on the electronic transport properties, and a comprehensive understanding of fundamental material parameters. The optical measurements for all the samples are shown in Fig. 5(b). The estimated optical band gap (Eg) is about 0.45 eV, which is in good agreement with literatures (0.5-0.6 eV)[65,71]. ...
... Temperature dependent figure of merit (ZT) for (Ag2Se)1-x(Bi2Se3)x is shown in Fig. 8(a). ZTs for all the samples increase with increasing temperature and x, due to the carrier concentration optimization. Thus, a peak ZT of 0.5 at 700 K is achieved for the sample with the highest carrier concentration. The SPB model further enables a prediction in carrier concentration dependent ZT at different temperatures using the experimental kL (Fig. 8(b)). The predicted ZT agrees well with the experimental data as shown in Fig. 8(b). It is found the highest carrier concentration obtained in this work is very close to the optimal one. According to the calculated band structure[71], engineering the band should enable a possibility for further enhancing the thermoelectric performance. ...
Vacancy and anti-site disorder scattering in AgBiSe2 thermoelectrics
2
2017
... Figure 7(c, d) show the temperature dependent total thermal conductivity (κ) and lattice thermal conductivity (κL) for (Ag2Se)1-x(Bi2Se3)x, respectively. κL is obtained by subtracting the electronic thermal conductivity (κE) from the total thermal conductivity via the Wiedemann-Franz Law, κE=LT/ρ, where L is the Lorenz factor determined by the SPB model with the acoustic phonon scattering. Both κ and κL decrease with increasing temperature. The κ slightly increase with increasing x due to the increased carrier concentration leading to higher κE. It is seen that the κL is lower than 0.7 W/(m·K) in the entire temperature range, mainly resulting from the strong anharmonicity[42,46,72] and strong phonon scattering by disorded cations[42,61,72]. The κL at high temperatures in the cubic phase is found to be as low as~0.4 W/(m·K), showing great potential for thermoelectric applications. ...
... ,72]. The κL at high temperatures in the cubic phase is found to be as low as~0.4 W/(m·K), showing great potential for thermoelectric applications. ...
Thermal conductivity of complex dielectric crystals
1
1973
... The sound velocities (vs) of longitudinal (vL) and transverse (vT) branches, as the important parameters determining kL, are measured and listed in Table 1. Moreover, the physical parameters including Debye temperature (qD), bulk modulus (B) and Grüeneisen parameter (g) are estimated based on the measured vL and vT[73,74], as listed in Table 1. It is shown that the change in sound velocities for all the samples does not exceed 5%, which is within the measurement uncertainty range. This excludes the influence of lattice softening on kL. This material shows a very low sound velocity of ~1500 m/s, one of the lowest sound velocities among thermoelectrics[39,75]. Moreover, the Grüneisen parameter (γ) as large as 2 indicates the strong anharmonicity[46]. Both the low sound velocity and the strong lattice anharmonicity could be the origin for the low κL observed. ...
Relation between the parameters of the elasticity theory and averaged bulk modulus of solids
1
2011
... The sound velocities (vs) of longitudinal (vL) and transverse (vT) branches, as the important parameters determining kL, are measured and listed in Table 1. Moreover, the physical parameters including Debye temperature (qD), bulk modulus (B) and Grüeneisen parameter (g) are estimated based on the measured vL and vT[73,74], as listed in Table 1. It is shown that the change in sound velocities for all the samples does not exceed 5%, which is within the measurement uncertainty range. This excludes the influence of lattice softening on kL. This material shows a very low sound velocity of ~1500 m/s, one of the lowest sound velocities among thermoelectrics[39,75]. Moreover, the Grüneisen parameter (γ) as large as 2 indicates the strong anharmonicity[46]. Both the low sound velocity and the strong lattice anharmonicity could be the origin for the low κL observed. ...
Mg3Sb2-based Zintl compound: a non-toxic, inexpensive and abundant thermoelectric material for power generation
1
2013
... The sound velocities (vs) of longitudinal (vL) and transverse (vT) branches, as the important parameters determining kL, are measured and listed in Table 1. Moreover, the physical parameters including Debye temperature (qD), bulk modulus (B) and Grüeneisen parameter (g) are estimated based on the measured vL and vT[73,74], as listed in Table 1. It is shown that the change in sound velocities for all the samples does not exceed 5%, which is within the measurement uncertainty range. This excludes the influence of lattice softening on kL. This material shows a very low sound velocity of ~1500 m/s, one of the lowest sound velocities among thermoelectrics[39,75]. Moreover, the Grüneisen parameter (γ) as large as 2 indicates the strong anharmonicity[46]. Both the low sound velocity and the strong lattice anharmonicity could be the origin for the low κL observed. ...
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