Zinc vanadates in vanadium oxide-doped zinc oxide varistors

Convergent-beam electron diffraction has been used to determine the space groups of β- and γ-Zn₃(VO₄)₂ particles in vanadium oxide-doped zinc oxide varistors. The crystal structure of β-Zn₃(VO₄)₂ has been determined to be monoclinic with space group P2₁ and lattice parameters of a = 9.80 angstroms, b = 8.34 angstroms, c = 10.27 angstroms, and β = 115.8°, whereas that of γ-Zn₃(VO₄)₂ is monoclinic with space group Cm and a = 10.40 angstroms, b = 8.59 angstroms, c = 9.44 angstroms, and β = 98.8°. Energy-dispersive X-ray microanalysis of these two phases shows significant deviations from their expected stoichiometry. It is apparent that the β-phase is, in fact, the metastable Zn₄V₂O₉ phase, whereas the γ-phase either is a new oxide that consists of zinc, vanadium, and manganese or, more likely, is a zinc vanadate phase with a Zn:V atomic ratio of 1:1 that has the ability to go into solid solution with manganese.