Ab initio lattice dynamics and thermodynamic properties of SrO under pressure

We present an ab initio calculation of lattice dynamics and thermodynamic properties of SrO in the NaCl (B1) and CsCl (B2) structured phases under pressure. We employ the density-functional perturbation theory (DFPT) within the local density approximation (LDA) in conjunction with the quasi-harmonic approximation. At zero pressure, the calculated dispersions agree well with the measured ones for the B1 phase. A pressure-induced soft transverse acoustic (TA) phonon mode is identified at the zone boundary X point of the Brillouin zone. The B2 phase is stable at high pressure. Our analysis suggest that this soft transverse mode is responsible for the pressure induced structural phase transition. The increase of the electronic dielectric function with pressure is attributed to the closure of the p–d gaps. The thermal expansion coefficient decreases with pressure and does not show any negative behavior. The predicted transition pressure decreases with temperature.

► The lattice dynamics of SrO and their pressure dependence in both B1 and B2 phases are investigated. ► The soft transverse acoustic phonon mode is responsible for the structural phase transition. ► The increase of the dielectric function with pressure is attributed to the closure of the p–d gaps. ► The temperature and pressure dependence of the thermal expansion coefficient is studied. ► The predicted transition pressure decreases with temperature.