Formation, structure and magnetism of the metastable defect fluorite phases AVO 3.5+x ( A=In, Sc)

Abstract

We report the preparation and stability of ScVO 3.5+ x and the novel phase InVO 3.5+ x. A VO 3.5+ x ( A=Sc, In) defect fluorite structures are formed as metastable intermediates during the topotactic oxidation of AVO 3 bixbyites. The oxidation pathway has been studied in detail by means of thermogravimetric/differential thermal analysis and in-situ powder X-ray diffraction. The oxidation of the bixbyite phase follows a topotactic pathway at temperatures between 300 and 400 °C in air/carbon dioxide. The range of accessible oxygen stoichiometries for the AVO 3.5+ x structures following this pathway are 0.00⩽ x⩽0.22. Rietveld refinements against powder X-ray and neutron data revealed that InVO 3.54 and ScVO 3.70 crystallize in the defect fluorite structure in space group Fm-3 m (227) with a=4.9863(5) and 4.9697(3)Å, respectively with A 3+/V 4+ disorder on the (4 a) cation site. Powder neutron diffraction experiments indicate clustering of oxide defects in all samples. Bulk magnetic measurements showed the presence of V 4+ and the absence of magnetic ordering at low temperatures. Powder neutron diffraction experiments confirmed the absence of a long range ordered magnetic ground state.