Neutron diffraction study, magnetism and magnetotransport of stoichiometric CaVO3 perovskite with positive magneto resistance

A stoichiometric calcium vanadium (IV) oxide with formula CaVO3 has been prepared by soft-chemistry procedures, followed by annealing under reducing conditions (H-2/N-2 flow). This material has been studied by X-ray and neutron powder diffraction (NPD), thermal analysis, magnetic and magnetotransport measurements. CaVO3.0 perovskite crystallizes in the orthorhombic Pbnm (No. 57) space group, with the GdFeO3-type structure. The unit-cell parameters are a = 5.3219(1) Angstrom, b = 5.3427(1) Angstrom and c = 7.5472(1) Angstrom. In this distorted perovskite the VO6 octahedra are tilted by 10.1degrees in order to optimize the Ca-O bond-lengths. A bond valence study from NPD data confirms the tetravalent oxidation state for V cations. The perovskite is fully oxygen stoichiometric. as demonstrated from thermal analysis and the refinement of the oxygen occupancy factors. The magnetic susceptibility is predominantly Pauli paramagnetic-like, although a non-negligible temperature-dependent. component due to isolated V4+ spins is patent at low temperatures. The transport measurements show a metallic behavior between 2 and 300 K; at low temperatures a positive rnagnetoresistance as large as 14% for H = 9 T is interpreted as the result of quantum interference effects. (C) 2004 Elsevier Inc. All rights reserved.