Optimization of Thermoelectric Transport Properties of Nb-doped Mo1-xWxSeTe Solid Solutions

doi:10.15541/jim20200135

Abstract

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

CLC Number:

TQ174

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.

Figures/Tables 15

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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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