Understanding The Interplay Of Vacancy, Cation, And Charge Ordering In The Tunable Sc2vo5+Delta Defect Fluorite System

We report the synthesis, structure, and redox behavior of the cation-ordered tetragonal Sc2VO5+delta defect fluorite superstructure previously thought to be the oxygen precise A(3+)2B(4+)O(5) phase. Four synthesis routes in oxidative, reductive, and inert atmospheres are demonstrated. Ex situ and in situ powder X-ray and neutron diffraction analyses reveal vanadium disproportionation reactions. The structure-reaction map illustrates the oxygen-dependent competition between the tetragonal cation and anion ordered Sc2VO5+delta and the disordered cubic Sc2VO5+delta' (delta < delta' = 0.5) phases as a function of temperature. Oxidation states and oxide stoichiometries were determined with DC magnetometry and XANES experiments. The tetragonal cation ordered Sc2VO5+delta phase with d = -0.15(2) for as-synthesized samples reveals vanadium charge ordering. V3+ and V4+ cations occupy octahedral sites, whereas V5+ predominantly occupies a tetrahedral site. The paramagnetic 8g{V-3+/(4)+}(4) clusters are isolated by diamagnetic 2cV(5+) cations. At temperatures below 500 degrees C the 8g{V3+/4+} 4 clusters can be topotactically fine-tuned with varying V3+/V4+ ratios. Above 600 degrees C the tetragonal structure oxidizes to the cubic Sc2VO5+delta' fluorite phase.its disordered competitor. The investigation of the cation- and anion-ordered ScV-O phases, their formation, and thermal stability is important for the design of low-temperature solid state oxide ion conductors and vacancy structures.