Search

The crystal structure of the new misfit-layer calcium cobaltite (CaOH)1.14CoO2 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)1.18TiS2. 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 (a1/a2 = 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. [ABSTRACT FROM AUTHOR]

Neutron powder diffraction patterns of deuterated sodium cobaltate, which shows superconductivity with Tc of about 4.5 K, show conspicuous diffuse maxima presumed to originate from the deuterated sodium part in addition to sharp reflections due to the CoO2 part. The structure is treated as an interpenetration of two layered subsystem structures, the CoO2 part (a1 = 2.83 Å) and the deuterated sodium part (a2 = 3.26 Å). A model of the short-range-order stacking of the deuterated sodium part is expressed using four possible configurations. The sequences in which neighbouring sheets have the same configuration do not occur, and the other sequences occur with the same probability. Diffuse scattering intensities simulated using the matrix method satisfactorily explain the neutron diffraction patterns. [ABSTRACT FROM AUTHOR]

High-pressure powder x-ray diffraction experiments have been carried out on iodine at room temperature with a helium-pressure medium. A new high-pressure phase has been found in the pressure range 24–28 GPa, in the close vicinity of the molecular dissociation. The structure is incommensurately modulated, which we interpret as a transient state between molecular and monatomic ones. [ABSTRACT FROM AUTHOR]