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Effects of MoO3 and WO3 on the structure and electronic transport in vanadium phosphate glasses

Electronic conduction has been demonstrated in various oxide glasses containing transition metal oxides (TMO) such as V2O5, MoO3, WO3, and Fe2O3. The electronic conductivity in these glasses arises from small polaron hopping between TM ions in different oxidation states and depends on the amount of TMO, the proportion of TM ions in different oxidation states, and the average distance between these ions. In this study, we investigate the influence of the addition of the second TMO on the electronic conductivity in vanadate-phosphate glasses. For that purpose, two series of ternary (60-x)V2O5–xTMO–40P2O5 glasses with a wide range of compositions: x = 0-60 mol% for TMO=WO3 and MoO3, were prepared by the melt quenching method. The structure and electrical properties of the prepared glasses were studied by Raman and impedance spectroscopy, and the thermal properties by Differential Thermal Analysis. The sum fraction of transition metal ions in the lower oxidation state was determined from the temperature dependence of magnetization. Interestingly, glass series show different behavior in the gradual substitution of V2O5 by TMO. While the addition of MoO3 conductivity continuously decreases over three orders of magnitude, it shows a deep minimum at 53 mol% WO3. The observed conductivity decrease over the entire range of mixed compositions in the case of MoO3 and WO3 is directly related to the decrease in the concentration of vanadium ions which play a dominant role in the polaron transport. It seems that molybdenum and tungsten ions in these glasses do not contribute to the electronic transport as much as vanadium and hence can not compensate for the decrease in V2O5 content. The high conductivity of binary WO3-P2O5 glass is related to the structural peculiarities of this glass system evidenced in the tendency of tungsten units to form clusters within which the transport of polarons is facilitated.

vanadium phosphate glass ; transition metal oxides ; electronic conductivity

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