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 C_ij 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 Bi ₂Te₃ 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.