SYNTHESIS, CRYSTAL-STRUCTURE AND TRANSPORT-PROPERTIES OF A NEW NONSTOICHIOMETRIC CAVO3+DELTA PHASE

A non-stoichiometric calcium vanadium(IV) oxide with formula CaVO3+delta has been synthesized via the thermal decomposition of the [Ca(VO)(+/- -C4H2O6)(H2O)(4)](2) metallo-organic precursor at 1073 K. The morphology of the samples obtained by using this method shows the influence of the transport vapour phase formed during the ligand pyrolysis. The oxide contains an excess of oxygen, delta= +0.23, which implies that the vanadium atom exhibits an oxidation state between V-IV and V-V. The crystal structure of CaVO3+delta is perovskite-type with orthorhombic distortion. This distortion modifies the symmetry of the [VO6] groups as was observed from the crystal refinement. The oxide presents a transition from semiconductor to metallic character at 78 K.