Enhancement of thermoelectric properties by lattice softening and energy band gap control in Te-deficient InTe1−δ

Song Yi Back,Kunihito Koumoto,Seokyeong Byeon,Hyungyu Jin,Hyunyong Cho,Jong-Soo Rhyee,Young-Kwang Kim

doi:10.1063/1.5063274

Abstract

The InTe has intrinsically low lattice thermal conductivity κL originating from the anharmonic bonding of In1+ ion in the lattice, which scatters the phonons. Here we report the enhancement of thermoelectric properties in Te-deficient InTe1−δ (δ = 0, 0.01, 0.1, and 0.2) polycrystalline compounds by lattice softening and energy band gap opening. Te-deficiency gives rise to more weak chemical bonding between In1+ atoms and In3+Te2− clusters than those of pristine InTe, resulting in the reduction of κL near the room temperature. The weak ionic bonding is confirmed by the increase of lattice volume from the X-ray diffraction and lattice softening by the decrease of Debye temperature with increasing Te-deficiency. We observed the low lattice thermal conductivity κL of 0.53 W m−1 K−1 at 300 K for InTe0.99, which is about 25 % decreased value than those of InTe. The Te-deficiency also induces energy band gap so that the electrical resistivity and Seebeck coefficient are increased due to the decrease of carrier concentration. Temperature-dependent thermoelectric properties shows the high Seebeck coefficient at high temperature and high electrical conductivity near room temperature, resulting in the temperature-insensitive high power factor S2σ over a wide temperature range. Owing to the temperature-insensitive high power factor and intrinsic low lattice thermal conductivity by Te-deficiency, the thermoelectric performances of figure-of-merit ZT and engineering ZTeng are enhanced at mild temperature range (≤550 K).

Highlights

Thermoelectricity is very promising technology for an energy harvesting and environmentally friendly cooling technology because thermoelectric materials can directly convert waste heat into electricity and drive temperature difference at two ends of thermoelectric materials that is applied to the solid state cooling
The performance of thermoelectric (TE) materials is defined by the dimensionless figure-of-merit ZT = S2σT /(κel + κL), where S, T, σ, κel, and κL are the Seebeck coefficient, absolute temperature, electrical conductivity, electronic thermal conductivity, and lattice thermal conductivity, respectively
Recent investigation shows that the phonon interaction with lone pair electrons results in low lattice thermal conductivity due to lattice anharmonicity

Summary

INTRODUCTION

Thermoelectricity is very promising technology for an energy harvesting and environmentally friendly cooling technology because thermoelectric materials can directly convert waste heat into electricity and drive temperature difference at two ends of thermoelectric materials that is applied to the solid state cooling. The cubic I-V-VI2 (where I = Cu, Ag, Au or alkali metal; V = As, Sb, Bi; and VI = Se, Te) compounds have intrinsically low κL due to strong anharmonicity originating from the lone-pair electrons of the group V atoms.[9,10] The s2 electrons on the group V atoms do not form sp[3] hybridized bonds and are isolated, which can be distorted by lattice vibrations leading to the lattice anharmonicity.[10] The enhancement in TE properties of AgSbSe2-based compounds have been mainly focused on the carrier concentration optimization by various dopants such as Ge,[11] Zn, Sb-deficient[13] and other doping materials.[14,15]. Owing to the improved power factor and decreased lattice thermal conductivity, the Tedeficient compounds of InTe1−δ enhances ZT and engineering ZT eng values over a wide temperature range

Synthesis

Measurements

Theoretical details

RESULTS AND DISCUSSION

CONCLUSION