Structure and properties of a novel cobaltate La0.30CoO2

The layered cobaltate La_0.30CoO₂ was prepared from Na_xCoO₂ 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 La_1/3CoO₂ introduces extra hole carriers into the diamagnetic LS Co³⁺ matrix making the sample Pauli paramagnetic. The temperature dependence of the electrical conductivity in La_0.30CoO₂ 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 La_0.30CoO₂ and related Na_xCoO₂ systems.