Ab initiopredicted metastable TlI-like phase in theB1toB2high-pressure transition of CaO

Abstract

Three different pathways have been analyzed, by periodic DFT-GGA-LCAO calculations, for the rocksalt-(B 1) to CsCl-type (B2) phase transformation of calcium oxide at the equilibrium pressure of 64.7 GPa. The monoclinic P2 1 /m mechanism shows a lower enthalpy barrier (0.13 eV) with respect to the other ones (R3m and Pmmn), and a secondary minimum in its enthalpy profile gives evidence of a metastable intermediate phase with TII-like structure and coordination number 7 for both Ca and 0. The changes of chemical bonding along the transition path are analyzed.