Hydrothermal synthesis and thermal stability of self-assembling NH4V3O7 microcrystals

Microcrystals of a new ammonium vanadate NH4V3O7 phase self-assembling into 3D-spherical particles were synthesized via the hydrothermal treatment of NH4VO3 (T = 180°C, 48 h) in the presence of citric acid. The morphology of NH4V3O7 particles was established to be governed by pH in the reaction mass. The compound crystallizes in monoclinic system with the unit cell parameters a = 12.247(5) A, b = 3.4233(1) A, c = 13.899(4) A, β = 89.72(3)°, V = 582.3(4) A3 (space group P21). The thermal stability and structural transitions of NH4V3O7 during its thermolysis under air and an inert atmosphere were determined.