First-principle calculation and quasi-harmonic Debye model prediction for elastic and thermodynamic properties of Bi2Te3

The influence of temperature and pressure on the mechanical and thermodynamic properties of single crystal Bismuth Telluride material was investigated by the first-principle calculation and quasi-harmonic Debye model. The computation results indicated that the lattice constant in the c axis increases nonlinearly and the elastic constants Cij and bulk module B0 increase linearly with increasing the pressure. The Young modulus of the Bi2Te3 crystal in the x and y axes are 28.6% larger than that in the z axis. The Poisson's ratios along the three axes range from 0.2752 to 0.3853. When the temperature is less than 150 K, the lattice specific heat capacity of Bi2Te3 depends on the temperature. The thermal expansion coefficients of Bi2Te3 vary remarkably with the temperature and pressure. The chemical balance bonding of Bi2Te3 is predicated to be Bi2+0.15Te-0.14Te2-0.08 based on the density functional theory, revealing the evident natural bonding interaction between Bi-Te and Te-Te. Those calculations are in good agreement with previous experimental data.