Anomalous conductivity and other properties of V₂O₅-P₂O₅ glasses with Bi₂O₃ OR Sb₂O₃

Abstract

To characterize the V₂O₅-P₂O₅ glasses with Bi₂O₃ or Sb₂O₃, the DC and AC conductivities, dielectric constants, SEM, X-ray diffraction, and DTA studies have been made. Electrical properties have been measured in the temperature range 80-420 K and in the frequency range 0.1-100 kHz. The DC conductivity of the 50V₂O₅(50-x)P₂O₅-xBi₂O₃ (x=5-40 mol%) glasses is found to be always higher than that of the pure base glass 50V₂O₅-P₂O₅, while the DC conductivity of the 50V₂O₅ -(50-x)P₂O₅-xSb₂O₃ glasses is always lower than that of the base glass. Above 200 K the activation energy of the V₂O₅-P₂O ₅-Bi₂O₃ glasses depends on the concentration of Bi₂O₃, while that of the V₂O₅-P₂O₅Sb₂O₃ glasses is almost independent of Sb₂O₃ concentration. However, both of these glasses show an interesting conductivity minimum for about 25-30 mol% of Bi₂O₃ or Sb₂O₃. This behavior was not found earlier in any such transition metal oxide glasses. The anomalous behavior, also observed in the concentration (Bi₂O₃ or Sb ₂O₃) dependence of the density, glass transition temperature T_g, AC conductivity, and dialectric constant data, is found to be associated with the lowest value of the ratio V⁵⁺/V⁴⁺ occurring at ~ 25-30 mol% of Bi ₂O₃ or Sb₂O₃. The AC conductivity is found to be proportional to ω^s, where ω is the frequency and s lying between 0.85 and 0.98, obtained from the theory based on the hopping-over barrier (HOB) model.