Structure and properties of (CaOH)kCoO2

We recently discovered two poly-type structural phases of the new cobalt-oxide system, (CaOH)1.14CoO2 and (Ca0.85OH)1.16CoO2. The former phase is an orthorhombic form, while the latter phase is monoclinic one. Both the phases have layered structure that consists of CdI2-type CoO2 triangle-lattice layers and rock-salt-type CaOH double-atomic-plane slabs, alternately stacked along the c-axis. The two subcells have incommensurate periodicity along the a-axis, resulting in a modulated crystal structure. Each structure of the two phases is composed by different stacking manner of the CoO2 blocks. The monoclinic phase accommodates hole-carriers generated by lattice defects of the Ca ions.