Modulated crystal structure of the composite crystal (CaOH)1.14CoO2

The crystal structure of the new misfit-layer calcium cobaltite (CaOH)(1.14)CoO2 was determined by means of superspace-group formalism using synchrotron X-ray diffraction data. The compound belongs to the class of incommensurate composite crystals that are isostructural to an orthorhombic form of sulfide, (PbS)(1.18)TiS2. The structure of the present compound consists of two interpenetrating subsystems: (i) [CoO2]-containing triangular lattices formed by edge-sharing CoO6 octahedra and (ii) [CaOH] double-layered rock-salt-type slabs. The two subsystems have incommensurate periodicity along the a-axis (a(1)/a(2) = 0.576), resulting in a modulated crystal structure due to the inter-subsystem interaction. In this study, it was found that there is a significant structural modulation in the [CaOH] subsystem.