From Bi4V2O11 to Bi4V2O10.66: The V-V-V-IV transformation in the Aurivillius-type framework

Bi4V2O11, the parent compound of the BIMEVOX family, has been studied by TEM and HREM, at room temperature and at high temperatures. Under the experimental conditions, Bi4V2O11 undergoes a V-V-V-IV reduction, ultimately leading to the formation of Bi6V3O16 (Bi4V2O10.66) with V-IV/V-V = 1/2. This transformation is confirmed by in situ X-ray diffraction studies of Bi4V2O11 under reducing atmospheres up to 330 degrees C. The symmetry of the alpha-Bi4V2O11 polymorph, stable at ambient temperature, is dependent on the chemical purity of V2O5 used for the synthesis.