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 Mottʹs 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.