Inverse-perovskite oxides Ca_3EO with E=Si, Ge, Sn, Pb: Structural, elastic and thermal properties

摘要

First-principles pseudo-potential plane-wave calculations have been performed for the first time in order to investigate the systematic trends for structural, elastic and thermal properties of the ideal cubic inverse-perovskite oxides Ca_3EO depending on the type of E atoms (E=Si, Ge, Sn, Pb). The computed equilibrium lattice constants are in excellent agreement with the experimental findings. Pressure dependence up to 40 GPa of the single-crystals and polycrystalline elastic parameters, namely, C11, C12, C44, bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio σ, and Lam's constants λ and μ, have been investigated in detail. The analysis of the BG ratios shows that all studied compounds can be classified as brittle materials. We have estimated the sound velocities in the principal directions: 100, 110 and 111. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the temperature and pressure effects on the lattice constant, bulk modulus, heat capacity and Debye temperature are performed.