Nb掺杂Mo1-xWxSeTe固溶体的热-电输运性能优化

doi:10.15541/jim20200135

摘要/Abstract

摘要：

固溶结合掺杂是优化材料热电性能的有效途径。本研究采用固相反应结合等离子体活化烧结成功合成了一系列单相的Mo_1-_xW_xSeTe(0≤x≤0.5)固溶体及其Nb掺杂产物。热电输运研究表明, W固溶结合Nb掺杂显著提高了Nb₂_yMo_0.5-_yW_0.5-_ySeTe固溶体的载流子浓度、载流子迁移率、电导率和功率因子, 适当降低了样品的晶格热导率, 进而显著提高了材料的热电优值ZT。随着Nb掺杂量的增加, 掺杂引入的离散能级转变为连续的杂质能带, 同步提升了载流子浓度和载流子迁移率。取向性研究发现, 由于在平行方向晶格热导率较低, Nb₂_yMo_0.5-_yW_0.5-_ySeTe固溶体在平行烧结压力方向的ZT略优。最优组分Nb_0.03Mo_0.485W_0.485SeTe在垂直于烧结压力和平行于烧结压力方向获得了最高ZT, 分别达到0.31和0.36(@823 K), 是目前MoSe₂基热电材料获得的最好结果之一。后续通过优化掺杂元素来改善Seebeck系数和功率因子, 将有望进一步提升MoSe₂基化合物的ZT。

关键词: Mo_1-_xW_xSeTe固溶体, Nb掺杂, 晶格热导率, 热电优值ZT

Abstract:

Solid solutions forming and doping is an effective approach to optimize the transport properties of thermoelectric materials. In this study, a series of single-phase Mo_1-_xW_xSeTe (0≤x≤0.5) solid solutions and their Nb-doped products were successfully synthesized with solid-state reaction followed by rapid sintering utilizing a Plasma Assisted Sintering apparatus. Thermoelectric transport studies showed that the carrier concentration, carrier mobility, electrical conductivity and power factor of the Nb₂_yMo_0.5-_yW_0.5-_ySeTe solid solutions were significantly increased by W substitution and Nb doping, while their lattice thermal conductivity was reduced, leading to remarkably enhanced dimensionless figure of merit ZT. The simultaneous increment of carrier density and carrier mobility with the increasing Nb content is due to the transition from discrete energy levels to continuous impurity band through Nb doping. The study of anisotropy indicated that, Nb₂_yMo_0.5-_yW_0.5-_ySeTe solid solutions owned a higher ZT value along the //P direction as a result of the lower lattice thermal conductivity. The Nb_0.03Mo_0.485W_0.485SeTe compound presented the highest ZT values among all samples, which were 0.31 and 0.36 (@823 K) along the ⊥p and //P directions, respectively, representing one of the best results based on MoSe₂-based materials. The enhancement of the Seebeck coefficient and the power factor is expected to further improve the ZT values of MoSe₂-based compounds by optimizing the doping elements.

Key words: Mo_1-_xW_xSeTe solid solutions, Nb doping, lattice thermal conductivity, thermoelectric figure of merit ZT

中图分类号:

TQ174

周星圆, 柳伟, 张程, 华富强, 张敏, 苏贤礼, 唐新峰. Nb掺杂Mo_1-_xW_xSeTe固溶体的热-电输运性能优化[J]. 无机材料学报, 2020, 35(12): 1373-1379.

ZHOU Xingyuan, LIU Wei, ZHANG Cheng, HUA Fuqiang, ZHANG Min, SU Xianli, TANG Xinfeng. Optimization of Thermoelectric Transport Properties of Nb-doped Mo_1-_xW_xSeTe Solid Solutions[J]. Journal of Inorganic Materials, 2020, 35(12): 1373-1379.

图/表 15

图1 Mo1-xWxSeTe(0≤x≤0.5)固溶体的XRD图谱

Fig. 1 XRD patterns of the prepared Mo1-xWxSeTe (0≤x≤0.5) solid solutions (a) Powder; (b) Bulk-⊥p; (c) Bulk-//P

图S1 Mo1-xWxSeTe(x=0.75和1)的粉末XRD图谱

Fig. S1 Powder XRD patterns of the prepared Mo1-xWxSeTe (x=0.75 and 1)

图S2 Mo1-xWxSeTe不同方向的断面SEM形貌

Fig. S2 SEM fractured surface morphologies of Mo1-xWxSeTe (a) x = 0, ⊥P; (b) x = 0, //P; (c) x = 0.25, ⊥P; (d) x = 0.25, //P; (e) x = 0.5, ⊥P; (f) x = 0.5, //P

图2 Mo1-xWxSeTe(0≤x≤0.5)晶格热导率κL随温度T的变化曲线

Fig. 2 Temperature dependent lattice thermal conductivities of Mo1-xWxSeTe (0≤x≤0.5) (a) ⊥p; (b) //P

图S3 Mo1-xWxSeTe 固溶体(0≤x≤0.5)沿⊥P和//P方向的(a, d)电导率σ, (b, e)塞贝克系数S和(c, f)热导率κ随温度变化的关系曲线

Fig. S3 Temperature dependence of (a, d) electrical conductivity σ, (b, e) Seebeck coefficient S, and (c, f) thermal conductivity κ of Mo1-xWxSeTe solid solutions (0≤x≤0.5) measured along the ⊥P and //P directions

表S1 1 Mo1-xWxSeTe(0≤x≤0.5)固溶体的组成、晶胞参数与光学带隙

Table S1 1 Compositions, cell parameters and optical band gaps of Mo1-xWxSeTe (0≤x≤0.5) solid solutions

Sample	Actual composition	Lattice parameters/nm	E_g/eV
x=0	MoSe_1.02Te_1.04	a=0.35, c=1.367	1.030
x=0.25	Mo_0.74W_0.25Se_0.9Te_0.96	a=0.3512, c=1.375	1.005
x=0.5	Mo_0.54W_0.46Se_0.93Te_0.94	a=0.3.5, c=1.371	0.998

表S2 2 Mo1-xWxSeTe(0≤x≤0.5)固溶体的取向因子LF

Table S2 2 LF factors of Mo1-xWxSeTe (0≤x≤0.5) solid solutions

Sample	P₀	P_⊥	LF
x=0	0.31	0.71	0.58
x=0.25	0.30	0.54	0.34
x=0.5	0.29	0.45	0.23

表S3 3 Nb2yMo0.5-yW0.5-ySeTe(0≤y≤0.035)固溶体的组成与晶胞参数

Table S3 3 Compositions and cell parameters of Nb2yMo0.5-yW0.5-ySeTe (0≤y≤0.035) solid solutions

Sample	Actual composition	Lattice parameters/nm
Mo_0.5W_0.5SeTe	Mo_0.54W_0.46Se_0.93Te_0.94	a=0.350, c=1.371
Nb_0.01Mo_0.495W_0.495SeTe	Mo_0.53W_0.47Se_0.99Te_1.09	a=0.351, c=1.371
Nb_0.03Mo_0.485W_0.485SeTe	Nb_0.03Mo_0.51W_0.46Se_0.93Te_0.96	a=0.351, c=1.370
Nb_0.05Mo_0.475W_0.475SeTe	Nb_0.04Mo_0.44W_0.52Se_0.97Te_0.95	a=0.352, c=1.371
Nb_0.07Mo_0.465W_0.465SeTe	Nb_0.05Mo_0.51W_0.43Se_0.90Te_0.86	a=0.352, c=1.371

图S4 Nb2yMo0.5-yW0.5-ySeTe(0≤y≤0.035)固溶体沿//P方向的(a)电导率σ, (b)塞贝克系数S, (c)功率因子PF, (d)热导率κ, (e)晶格热导率κL和(f)ZT值随温度变化的关系曲线

Fig. S4 Temperature dependence of (a) electrical conductivity σ, (b) Seebeck coefficient S, (c) power factor PF, (d) thermal conductivity κ, (e) lattice thermal conductivity κL and (f) the ZT values of Nb2yMo0.5-yW0.5-ySeTe (0≤y≤0.035) solid solutions measured along the //P direction

图3 Nb2yMo0.5-yW0.5-ySeTe(0≤y≤0.035)的粉末XRD图谱

Fig. 3 Powder XRD patterns of the prepared Nb2yMo0.5-yW0.5-ySeTe (0≤y≤0.035) solid solutions

表1 Nb2yMo0.5-yW0.5-ySeTe (0≤y≤0.035)固溶体的组成和室温热电输运性质

Table 1 Compositions and transport parameters of Nb2yMo0.5-yW0.5-ySeTe (0≤y≤0.035) solid solutions at room temperature

Sample	Actual composition	p/(×10²⁰, cm^-3)	μ/(cm²·V^-1·s^-1)		σ/(×10⁴, S·m^-1)		S/(μV·K^-1)
Sample	Actual composition	p/(×10²⁰, cm^-3)	⊥P	//P	⊥P	//P	⊥P	//P
y=0	Mo_0.54W_0.46Se_0.93Te_0.94	0.16	0.79	0.26	0.02	0.01	22.4	42.0
y=0.005	Mo_0.53W_0.47Se_0.99Te_1.09	1.53	1.37	1.32	0.33	0.32	17.2	15.1
y=0.015	Nb_0.03Mo_0.51W_0.46Se_0.93Te_0.96	5.96	2.95	2.52	2.82	2.40	102	93.1
y=0.025	Nb_0.04Mo_0.44W_0.52Se_0.97Te_0.95	6.61	5.45	4.80	5.76	5.07	65.9	70.9
y=0.035	Nb_0.05Mo_0.51W_0.43Se_0.90Te_0.86	7.63	5.72	4.29	6.98	5.24	53.2	52.0

图4 Nb2yMo0.5-yW0.5-ySeTe(0≤y≤0.035)固溶体的(a)电导率s, (b)塞贝克系数S和(c)功率因子PF随温度的变化关系曲线, (a)中插图为Nb掺杂后引入的杂质能级示意图。

Fig. 4 Temperature dependence of (a) electrical conductivity s, (b) Seebeck coefficient S and (c) power factor PF of Nb2yMo0.5-yW0.5-ySeTe (0≤y≤0.035) solid solutions with inset in (a) showing the impurity states introduced by the Nb doping.

图5 Nb2yMo0.5-yW0.5-ySeTe(0≤y≤0.035)与文献报道的其它化合物的Pisarenko曲线对比

Fig. 5 Pisarenko plots for Nb2yMo0.5-yW0.5-ySeTe (0≤y≤0.035) samples compared with the reported data

图6 Nb2yMo0.5-yW0.5-ySeTe(0≤y≤0.035)固溶体的(a)热导率κ, (b)晶格热导率κL和(c)ZT值随温度变化关系曲线

Fig. 6 Temperature dependent (a) thermal conductivity κ, (b) lattice thermal conductivity κL and (c) figure of merit ZT for Nb2yMo0.5-yW0.5-ySeTe (0≤y≤0.035) solid solutions

图S5 Nb2yMo0.5-yW0.5-ySeTe(y=0.015和0.025)固溶体和文献报道的Nb0.05Mo0.95SeTe和Ta0.05Mo0.95Se2沿⊥p和//P方向的热电性能比较

Fig. S5 Comparison of thermoelectric properties along ⊥p and //P directions among Nb2yMo0.5-yW0.5-ySeTe solid solutions with y=0.015 and 0.025 as well as Nb0.05Mo0.95SeTe and Ta0.05Mo0.95Se2 in the previous reports (a) Electrical conductivity s; (b) Seebeck coefficient S; (c) Power factor PF; (d) Thermal conductivity κ; (e) Lattice thermal conductivity κL; (f) ZT

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