Single-crystal study of topotactic changes between NH4VO3 and V2O5

Abstract

In the thermal decomposition of NH₄VO₃ to V₂O₅, the changes in crystallographic orientation were studied by using single crystals of NH₄VO₃ prepared by recrystallization from aqueous solution. X-Ray diffraction (XRD) measurements clearly showed that a shrinkage took place along b axis of NH₄VO₃ up to 180 °C and V₂O₅ sheets started to be formed in parallel to ab plane of NH₄VO₃ above 205 °C. These changes in crystallographic orientation were confirmed through the reverse reactions to NH₄VO₃. Crack formation during the decomposition, observed with scanning electron microscopy (SEM), was consistent with the topotactic changes observed.