Formation, structure and magnetism of the metastable defect fluorite phases AVO3.5+x (A=In, Sc)

We report the preparation and stability of ScVO3.5+x and the novel phase InVO3.5+x. AVO3.5+x (A=Sc, In) defect fluorite structures are formed as metastable intermediates during the topotactic oxidation of AVO3 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 AVO3.5+x structures following this pathway are 0.00⩽x⩽0.22. Rietveld refinements against powder X-ray and neutron data revealed that InVO3.54 and ScVO3.70 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 A3+/V4+ disorder on the (4a) cation site. Powder neutron diffraction experiments indicate clustering of oxide defects in all samples. Bulk magnetic measurements showed the presence of V4+ and the absence of magnetic ordering at low temperatures. Powder neutron diffraction experiments confirmed the absence of a long range ordered magnetic ground state.

Topotactic oxidation of AVO3 bixbyite to AVO3.5 defect fluorite structure followed by in-situ powder X-ray diffraction. The upper structural diagram shows a six coordinated (A/V)-O6 fragment in bixbyite, the lower structure illustrates the same seven-fold coordinated (A/V)-O7 cubic environment in the defect fluorite structure.Figure optionsDownload as PowerPoint slide