Optimization of Thermoelectric Properties of SnTe via Multi-element Doping

doi:10.15541/jim20240062

Abstract

Abstract:

Thermoelectric materials can realize the direct conversion of heat and electric energy, and have broad application prospects in the fields of thermoelectric power generation and semiconductor refrigeration. Both SnTe and PbTe thermoelectric materials belong to the Ⅳ-Ⅵ group, and have the same NaCl-type crystal structure, but SnTe possesses poor thermoelectric properties. In this work, SnTe-based thermoelectric materials were prepared by a fast method, known as self-propagating high-temperature synthesis under high-gravity field (HG-CS) combined with spark plasma sintering (SPS). The effect and mechanism of multi-element doping on the thermoelectric properties of SnTe compounds were also studied. Multi-element doping, equivalent ions Ge²⁺ and Pb²⁺ in cation of SnTe and anionic S^2- and Se^2-, causes a large number of lattice distortion point defects. At the same time, rapid solidification under the supergravity field brings about plastic deformation and introduces a stress field and a large number of dislocations, which results in the formation of multilevel microstructural defects and strong scattering of medium- and high-frequency phonons. As a result, the room-temperature thermal conductivity decreases dramatically from 7.28 W·m^-1·K^-1 (undoped SnTe) to 2.74 W·m^-1·K^-1 (Sn_0.70Ge_0.15Pb_0.15Te_0.80Se_0.10S_0.10), with a minimum thermal conductivity of only 1.38 W·m^-1·K^-1 at 873 K. These microstructural defects scatter phonons and carriers, leading to a decrease in carrier mobility and conductivity. It is worth mentioning that doping decreases the bandgap of SnTe and increases the Seebeck coefficient, so that the power factor PF of the doped material remains at a high value. Finally, the peak thermoelectric figure of merit ZT of Sn_0.70Ge_0.15Pb_0.15Te_0.80Se_0.10S_0.10 sample is greatly improved to 1.02 (873 K).

Key words: tin telluride, thermoelectric material, entropy engineering, combustion under high-gravity field

CLC Number:

TB34

SU Haojian, ZHOU Min, LI Laifeng. Optimization of Thermoelectric Properties of SnTe via Multi-element Doping[J]. Journal of Inorganic Materials, 2024, 39(10): 1159-1166.

Figures/Tables 8

Fig. 1 Schematic diagrams of preparative principles (a) Raw material filling in the reaction chamber; (b) Equipment for high gravity field assisted combustion synthesis

Fig. 2 XRD patterns of Sn0.70Ge0.15Pb0.15Te1-2xSexSx (x=0.05, 0.07, 0.10) samples (b) Magnified patterns of 2θ=28°-30°

Fig. 3 SEM images (a-c) and EDS spectra (d-e) of Sn0.70Ge0.15Pb0.15Te0.80Se0.10S0.10 Colorful figures are available on website

Fig. 4 Relationship of entropy change (∆S) and x in Sn0.70Ge0.15Pb0.15Te1-2xSexSx ∆S1: Entropy change of SnTe; ∆S2: Entropy change of Sn0.85Ge0.15Te; R: Gas constant, 8.314 J·mol-1·K-1

Fig. 5 Electrical transport performance for bulk SnTe, Sn0.85Ge0.15Te, Sn0.70Ge0.15Pb0.15Te and Sn0.70Ge0.15Pb0.15Te1-2xSexSx (x=0.05, 0.07, 0.10) samples (a, c, d) Temperature dependence of (a) Seebeck coefficient, (c) electrical conductivity and (d) power factor; (b) Dependence of Seebeck coefficient on the entropy change

Fig. 6 Thermal transport performance for bulk SnTe, Sn0.85Ge0.15Te, Sn0.70Ge0.15Pb0.15Te and Sn0.70Ge0.15Pb0.15Te1-2xSexSx (x=0.05, 0.07, 0.10) samples (a) Temperature dependence of thermal conductivity; (b) Lattice thermal conductivities at 298, 573 and 873 K as a function of the number of alloying elements

Fig. 7 Microstructure of the sample Sn0.70Ge0.15Pb0.15Te0.80Se0.10S0.10 (a) Low magnification TEM image; (b) HRTEM image of the selected area 1 in (a); (c) Inverse fast Fourier transform (IFFT) and geometric phase analysis (GPA) images of the selected area 2 in (b)

Fig. 8 Temperature dependence of ZT for bulk SnTe, Sn0.85Ge0.15Te, Sn0.70Ge0.15Pb0.15Te, Sn0.70Ge0.15Pb0.15Te1-2xSexSx (x=0.05, 0.07, 0.10), and samples in literature[32-33] Colorful figure is available on website

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