Ab initio study of the mechanical properties and thermal conductivity of Bi2O2X (X = Se, Te) under pressure

Abstract

The structural and mechanical properties, and thermal conductivity of Bi2O2X (X = Se, Te) under pressures ranging up to 50 GPa were evaluated by first-principles calculations based on the density functional theory. The calculated lattice parameters and cell volume of Bi2O2Se and Bi2O2Te in the ground state are in good agreement with the available experimental and theoretical data. Moreover, the calculated elastic constants indicate that both Bi2O2Se and Bi2O2Te are mechanically stable at least up to 50 GPa. When the pressure is increased up to 60 GPa, the calculated elastic constants of these two materials fail to satisfy the mechanical stability criteria, indicating that phase transition might have occurred. In addition, further studies on the elastic properties under pressure reveal that both Bi2O2Se and Bi2O2Te show ductility within the pressure range investigated in this study. Meanwhile, the shear modulus, Young's modulus, and sound velocities of these two materials are all anisotropic in the ground state, and their anisotropic characteristics became increasingly significant with an increase in pressure. Finally, the minimum thermal conductivities and the anisotropy of Bi2O2Se and Bi2O2Te under pressure are further analyzed using Clarke's and Cahill's models. The results show that both these materials are potential anisotropic thermoelectric materials.