Crystal structure of post-perovskite-type CaIrO(3) reinvestigated: new insights into atomic thermal vibration behaviors

Single crystals of the title compound, the post-perovskite-type CaIrO(3) [calcium iridium(IV) trioxide], have been grown from a CaCl(2) flux at atmospheric pressure. The crystal structure consists of an alternate stacking of IrO(6) octa­hedral layers and CaO(8) hendeca­hedral layers along [010]. Chains formed by edge-sharing of IrO(6) octa­hedra (point-group symmetry 2/m..) run along [100] and are inter­connected along [001] by sharing apical O atoms to build up the IrO(6) octa­hedral layers. Chains formed by face-sharing of CaO(8) hendeca­hedra (point-group symmetry m2m) run along [100] and are inter­connected along [001] by edge-sharing to build up the CaO(8) hendeca­hedral layers. The IrO(6) octa­hedral layers and CaO(8) hendeca­hedral layers are inter­connected by sharing edges. The present structure refinement using a high-power X-ray source confirms the atomic positions determined by Hirai et al. (2009 ▸) [Z. Kristallogr. 224, 345–350], who had revised our previous report [Sugahara et al. (2008 ▸). Am. Mineral. 93, 1148–1152]. However, the displacement ellipsoids of the Ir and Ca atoms based on the present refinement can be approximated as uniaxial ellipsoids elongating along [100], unlike those reported by Hirai et al. (2009 ▸). This suggests that the thermal vibrations of the Ir and Ca atoms are mutually suppressed towards the Ir⋯Ca direction across the shared edge because of the dominant repulsion between the two atoms.