Synthesis, crystal structure and transport properties of a new non-stoichiometric CaVO_3+δ phase

A non-stoichiometric calcium vanadium(iv) oxide with formula CaVO _3+δ 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, δ= +0.23, which implies that the vanadium atom exhibits an oxidation state between V^IV and V^V. The crystal structure of CaVO_3+δ 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.