Mechanochemical synthesis of crystalline compounds in the Bi-V-O system

The phase composition of crystalline mechanochemical synthesis products in the Bi2O3-V2O5 system is determined by x-ray diffraction. The phases identified are sillenite, clinobisvanite, a fluorite phase, the high-temperature form of the Aurivillius phase gamma-Bi2VO5.5-x, and new, metastable tetragonal fluorite-like solid solutions. The same compounds are obtained at other Bi : V ratios using Bi2O4 and VO2 as starting reagents. Structural analysis of the synthesized compounds reveals high vacancy concentrations and substitutional disorderin The room-temperature ESR spectra of the samples show V4+ signals at g similar or equal to 2 and 4. The phase transitions characteristic of clinobisvanite and gamma-Bi2VO5.5-x, are not detected by thermal analysis, in line with the structural data. Mechanical activation of high-purity alpha-Bi2O3 Converts it into the beta form; in the presence of impurities, the resulting phases have fluorite or slightly distorted fluorite-like structure.