Study of lattice vibration and thermal conductivity of BiCuSeO from first-principles calculations
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Study of lattice vibration and thermal conductivity of BiCuSeO from first-principles calculations Jingxuan Ding1, Ben Xu1, 2, and Yuanhua Lin1 1 School of materials science and engineering, Tsinghua University, Beijing 100084, P.R. China. 2 Key laboratory of Advanced Materials of Ministry of Education of China, Tsinghua University, Beijing 100084, P.R. China. ABSTRACT The BiCuSeO has been proved to be one of the best oxide-based thermoelectric materials in recent years. Its electric properties have been widely studied, yet the lattice thermal conductivity was only discussed roughly. Our investigation suggests that the anharmonic vibration and the interlayer-interaction plays the crucial role in reducing the intrinsic lattice thermal conductivity. The thermal conductivity has been calculated based on quasi-harmonic approximation and detailed contribution have been discussed. The calculated data have good agreement with the experimental data. INTRODUCTION Thermoelectric materials can achieve mutual conversion of thermal and electrical energy directly. Such advantage ensure their potential application in energy reserving and temperature controlling. The Thermoelectric conversion efficiency can be characterized by dimensionless figure of merit ZT=S2σ/κ, where S, σ, κ, and T are the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively. This simple equation provides researchers with several obvious objectives, as improving the power factor and reducing the thermal conductivity. However, these properties are structural dependent and it's impossible to improve simultaneously. Thus, to get a promising thermoelectric materials, one can either search for materials with high electrical properties, find approaches to reduce the thermal conductivity, or optimize the power factor of those with intrinsic low thermal conductivity. Recently, the layered compound BiCuSeO have been found to exhibit fascinating thermoelectric properties. It was reported that the figure of merit of pristine BiCuSeO can reach 0.70 at 773K.1 Besides, as a p-type semiconductor, its electrical properties can be improved by doping bivalence metals like Mg, Ca, Sr and Ba.2-5 By doping heavy metal Ba, the ZT value of BiCuSeO can reach 1.1 at 923 K. By introducing Cu deficiencies, electrical conductivity can be improved while maintaining the Seebeck coefficient and low thermal conductivity, resulting in a ZT value of 0.81 at 923 K. 6 Liu et al. investigated the influence of Pb substitution at the Bi sites and achieve a ZT value of 1.14 at 823 K. 7 Sui et al. synthesized textured BiCuSeO and reach a ZT value of 1.4 at 923 K, which is one of the latest progress of the system. 8 On the theoretical side, the electronic structure of BiCuSeO was investigated by Stampler et al. after pristine BiCuSeO was synthesized. The density of states (DOS) and band structure of BiCuSeO were compared with BiCuSO, and the lone pair-like ns electrons at the valence band maximum (VBM) were discussed, 9 and the enhancement of power
