Ab initio calculations on structural, elastic and dynamic stability of CdO at high pressures

Abstract

First principles calculations have been carried out to analyze structural, elastic, and dynamic stability, of CdO under hydrostatic compression. The comparison of enthalpies of rocksalt type (B1) and CsCl type (B2) structures determined as a function of compression suggests the B1 → B2 transition at ∼87 GPa, in good agreement with experimental value of 90.6 GPa [Liu et al. Phys. Rev. B 70, 0941141 (2004)]. Various physical quantities, such as zero pressure equilibrium volume, bulk modulus, pressure derivative of bulk modulus, Gruneisen parameter, and Debye temperature have been derived from the theoretically determined equation of state. All these physical quantities show a reasonably good agreement with the available experimental data. Additionally, employing the theoretically determined thermal equation of state in conjunction with Rankine Hugoniot relation, we have predicted the Hugoniot of B1 phase of this material. The single crystal elastic constants of B1 phase calculated up to the pressure of 166 GPa show that though, the shear elastic stability of B1 phase decreases monotonically with compression, it still remains stable elastically even at transition point. Our lattice dynamic calculations show that the B1 phase remains stable dynamically also for pressures <118 GPa. For B2 phase, our calculations demonstrate that this structure will be elastically stable beyond ∼38 GPa. However, to stabilize this phase dynamically a still higher pressure of ∼55 GPa will be required, which is less than B1 → B2 transition pressure.