The crystal structure of CaIrO₃ post-perovskite revisited

Abstract

The structure of CaIrO₃ post-perovskite has been determined using CAD4 and Bruker SMART diffractometers for two different crystals. In both cases the structure was solved by Direct Methods which revealed all four atoms in the asymmetric unit. Anisotropic refinement of all atoms gave (CAD4/SMART): R₁ = 0.016/0.008, wR₂ = 0.032/0.009. There is excellent agreement between the structure models of the two studies. However, some notable differences were found between the structures determined here and that reported by Sugahara et al., (2008): most obviously, we observe no significant anisotropic displacements for any of the atoms. Anisotropic displacement parameters for Ca, Ir and O atoms are very similar to those of their counterparts in MgSiO₃ perovskite. The close similarity of the structures of the two crystals determined here using two very different diffractometers suggests that the derived model structure reported here is better-constrained and more representative of the characteristic features of CaIrO₃ post-perovskite than that obtained by Sugahara et al., (2008).