The Electronic Structure And Thermoelectric Properties Of Alkali Metal Doped Bismuth Telluride

The key research field of thermoelectric materials is to improve the conversion efficiency of thermoelectric material. Doping is an effective method to improve the thermoelectric materials value. Bi2Te3is one of the earliest and most mature of thermoelectric materials. It has the best thermoelectric properties at room temperature, has been widely applied in the field of thermal power industry. This paper is mainly based on the density functional theory and the semiclassical Boltzmann theory, we research the electronic structure and thermoelectric properties of the (Bi,Sb)2(Te,Se)3doped system and alkali metal element Na doped Bi2Te3system. The main research content and innovation are as follows:1. We investigated the geometry optimization and electronic structure of (Bi,Sb)2(Te,Se)3doped system. A larger1×1×3supercell with nominal formula Bi6Te9is proposed, in order to ensure the accuracy of calculation. We calculated the total density of states, partial density of states and energy band structure based on the density functional theory and the first principle method. And analyses the influence on energy band structure by introducing spin-orbit coupling effect on different atomic. We also studied the relationship between the density of states near the Fermi level and the Sebek coefficient.2. We investigated the thermoelectric properties of four kinds of (Bi,Sb)2(Te,Se)3model. By using Boltzmann theory and the constant relaxation time approximation, we calculate the Seebeck coefficient, the conductivity, and power factor, we also analyses the influence of doping position for system thermoelectric properties. Because Bi2Te3is a typical anisotropic material, we calculated and compared the thermoelectric properties in the xx direction and zz direction. Finally, we get the thermoelectric figure of merit by n doped and p doped of four kinds of (Bi,Sb)2(Te,Se)3models near the Fermi level. The optimal ZT value can be obtained by means of suitable experment to adjust the carrier concentration.3. We investigated the electronic structure and thermoelectric properties of Na doped Bi2Te3system. We used a2x2x2supercell as our computational model, and design of the6.25%Na atoms doping ratio. The spin orbit interaction is very important for analysis the electronic structure of heavy metal elements system, we also analyse the influence on energy band structure by the introduction of alkali metal. Then we calculate and analyse the thermal transmission coefficient of NaBi15Te24system, according to the semiclassical Boltzmann transport theory and the relaxation time approximation method. We also research the influence on thermoelectric properties by doping Na atoms for NaBi15Te24system.