Structure and properties of a novel cobaltate La0.30CoO2

The layered cobaltate La0.30CoO2 was prepared from NaxCoO2 precursor by a solid-state ionic exchange and was characterized by means of X-ray and neutron diffraction, magnetic, thermal and electric transport measurements. The compound consists of hexagonal sheets of edge-sharing CoO6 octahedra interleaved by lanthanum monolayers. Compared to Na+ in the parent system, the La3+ ions occupy only one-third of available sites, forming a 2-dimensional superstructure. The deviation from the ideal stoichiometry La1/3CoO2 introduces extra hole carriers into the diamagnetic LS Co3+ matrix making the sample Pauli paramagnetic. The temperature dependence of the electrical conductivity in La0.30CoO2 follows Mott's T−1/3 law up to about 400 K, which is in contrast with the standard metallic behavior in the Na+ homolog possessing the same formal doping. The experiments are complemented by electronic structure calculations for La0.30CoO2 and related NaxCoO2 systems.

Optimized superstructure of La0.3CoO2 obtained by LDA calculation.Figure optionsDownload as PowerPoint slideHighlights
► A novel layered cobaltate La0.30CoO2 was prepared by a solid-state ionic exchange.
► La3+ ions are ordered and form a 2-dimensional superstructure.
► Electrical conductivity of variable range hopping type up to 400 K.