title: Crystal structure of post-perovskite-type CaIrO3 reinvestigated: new insights into atomic thermal vibration behaviors.
abstract: Single crystals of the title compound, the post-perovskite-type CaIrO3 [calcium iridium(IV) trioxide], have been grown from a CaCl2 flux at atmospheric pressure. The crystal structure consists of an alternate stacking of IrO6 octa-hedral layers and CaO8 hendeca-hedral layers along [010]. Chains formed by edge-sharing of IrO6 octa-hedra (point-group symmetry 2/m..) run along [100] and are inter-connected along [001] by sharing apical O atoms to build up the IrO6 octa-hedral layers. Chains formed by face-sharing of CaO8 hendeca-hedra (point-group symmetry m2m) run along [100] and are inter-connected along [001] by edge-sharing to build up the CaO8 hendeca-hedral layers. The IrO6 octa-hedral layers and CaO8 hendeca-hedral layers are inter-connected 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.
authors.affiliation: Graduate School of Science and Engineering, Yamaguchi University, Ube 755-8611, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Nakatsuka
authors.affiliation: Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Sugiyama
authors.affiliation: Institute for Study of the Earth's Interior, Okayama University, Misasa 682-0193, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Yoneda
authors.affiliation: Graduate School of Science and Engineering, Yamaguchi University, Ube 755-8611, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Fujiwara
authors.affiliation: Graduate School of Science and Technology, Kumamoto University, Kumamoto 860-8555, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Yoshiasa
keywords: calcium iridium(IV) trioxide; crystal structure; post-perovskite; redetermination; thermal vibration