Mg_2Si的电子结构和热电输运性质的理论研究

Theoretical investigation of the electronic structure and thermoelectric transport property of Mg_2Si

利用全势线性缀加平面波法,对Mg2Si的几何结构和电子结构进行了计算,得到了稳定的晶格参数以及能带和电子态密度.能带结构表明,Mg2Si为间接带隙半导体,禁带宽度为0.20eV.在此基础上利用玻尔兹曼输运理论和刚性带近似计算了材料的电导率、Seebeck系数和功率因子.结果表明,在温度为700K时p型和n型掺杂的Mg2Si功率因子达到最大时的最佳载流子浓度分别为7.749×1019cm-3和1.346×1020cm-3.结合实验热导参数,估算了700K时最高热电优值ZT可以达到0.93.通过对比不同温度下的输运系数发现,功率因子与弛豫时间之比的极大值随温度升高而增大,在中高温区使用材料的最佳掺杂浓度要高于低温区使用材料的最佳掺杂浓度.

Full-potential linearized augmented plane wave method and Boltzmann transport properties have been used to investigate the crystal structure and electronic structure of Mg2Si. Electronic conductivity,Seebeck coefficient and power factor are calculated. Energy band structure shows that Mg2Si is an indirect semiconductor with energy band gap of about 0. 20 eV. Transport properties versus the doping level have been calculated for the n type and p type doped materials at 700 K. The optimal carrier concentration corresponding to the maxima of power factor are obtained,which are 7. 749 × 1019 cm-3 and 1. 346 × 1020 cm-3 for the p-doping and n-doping respectively. Maximum ZT value of 0. 93 has been estimated in combination with experimental data of thermal conductivity. From the transport properties at different temperatures,we found that the ratio of power factor to relaxation time is enhanced when the temperature increases. Optimum doping level of materials used in middle and high temperature range is higher than that of materials used in low temperature.