First Principles Study Of Bi₂Te₃ Structural Distortion Under Pressure And Improvement On Thermoelectric Properties

Thermoelectric materials, as a function materialcan convert thermal energy to electrical energy directly, has important value and a wide range of applications. Although thermoelectric power generations and refrigeration equipment have many benefits such as not polluting the environment, small size, high reliability and suitable temperature range but the low efficiency atenergy conversion is the fatal weakness which limited the usage of thermoelectric materials. Therefore, how to improve the efficiency is the key to the study of thermoelectric materials. Nowadays, using high pressure tactics to increase the conversion efficiency is one of the hot topics.Bi₂Te₃ as one of the most commonly used thermoelectric materials are widely used and research. It is reported recently that the ratio between c axis and a axis of Bi₂Te₃ hexagon lattice, the c/a, occur a concave shape changewith the increasing pressure and the lattice distortion may lead to the improvement of its thermoelectric properties. But it is still ambiguous that the mechanism of this kind of distortion and the truth of its increasing thermoelectric properties caused by the distortion.This article, based on density functional theory (DFT) and pseudo potential augment plane wave (PP-APW),simulate the lattice structure and parameters and the c/a occur a concave shape change with the increasing pressure which is the same as the experimental result. The increase of electric density between neighboring Te1 atoms result in the rapid decreasing of the distance between Te1 atom layers which leads to the c/a anomalies.The distortion of lattice also changes the microscopic electric structure. The position of the bottom of conduction band has changed and the effective masses of the conduction band and valence band both decrease with the increasing pressure.The lattice distortion changes the band structure and the density of state, which has effect on the thermoelectric properties of Bi₂Te₃.The Seebeck coefficientsdecreases with increasing pressure while the conductivity increase. The peak of ZT value of n-type materials higher with increasing pressure, while for p-type the peak of ZT value decrease.