High-pressure X-ray diffraction and Raman spectroscopy of CaFeO-type β-CaCrO

In situ high-pressure synchrotron X-ray diffraction and Raman spectroscopic studies of orthorhombic CaFeO-type β-CaCrO chromite were carried out up to 16.2 and 32.0 GPa at room temperature using multi-anvil apparatus and diamond anvil cell, respectively. No phase transition was observed in this study. Fitting a third-order Birch–Murnaghan equation of state to the data yields a zero-pressure volume of  = 286.8(1) Å, an isothermal bulk modulus of  = 183(5) GPa and the first pressure derivative of isothermal bulk modulus ′ = 4.1(8). Analyses of axial compressibilities show anisotropic elasticity for β-CaCrO since the -axis is more compressible than the - and -axis. Based on the obtained and previous results, the compressibility of several CaFeO-type phases was compared. The high-pressure Raman spectra of β-CaCrO were analyzed to determine the pressure dependences and mode Grüneisen parameters of Raman-active bands. The thermal Grüneisen parameter of β-CaCrO is determined to be 0.93(2), which is smaller than those of CaFeO-type CaAlO and MgAlO.