Pressure dependent structural phase transition and observation of Dirac-like dispersions in CaTe and SrTe

Abstract

At ambient pressure both CaTe and SrTe are known to exist in NaCl type structure (B1 phase) and undergo structural transition at high pressure to CsCl type structure (B2 phase). Most theoretical studies presented regarding the structural transition from B1 to B2 phase are based upon enthalpy comparisons. In this paper, we have computed elastic constants C11, C12, and C44 for both phases at various pressures and used Born stability conditions to compare the relative mechanical stability of both phases with pressure. The dynamical stability of these structures has been investigated using phonon dispersion calculations at different pressures. Our study finds that phonon dispersion calculations match well with enthalpy based predictions for the transition from B1 to B2 phase. Moreover, the Born stability conditions are necessary but not sufficient conditions to predict the structural stability of a crystal. Both CaTe and SrTe are 3D Dirac metals in the B2 phase and exhibit linear dispersions of electronic states near the Fermi level.