Compression, thermal expansion, structure, and instability of CaIrO3, the structure model of MgSiO3 post-perovskite

Analysis of pressure-temperature dependent monochromatic X-ray powder diffraction data yield the bulk modulus [K-T = 180.2(28) GPa] and thermal expansion coefficients [alpha(0) 2.84](34) x 10(-5) K-1; alpha(1) = 3.37(48) x 10(-9) K-2] of CaIrO3, the structure model for post-perovskite MgSiO3 center dot CaIrO3 is orthorhombic (Cmcm, space group 63, Z = 4) with best-fit unit-cell parameters, a = 3.14147(5) angstrom, b = 9.87515(19), c = 7.29711(11), and V = 226.3754(78) angstrom(3) at 1 bar and 300 K. The c-axis of CaIrO3 has a small compressibility and a large thermal expansion when compared to the other principal axes. Rietveld structure refinement reveals changes in CaIrO, as a function of temperature in terms of IrO6 octahedra distortion. Dissociation of CaIrO3, at high temperature has possible implications for the post-perovskite MgSiO3 structure, Earth's lower mantle, and D '' layer.