Influence of copper on electrical conductivity of glass-ceramics based on vanadium dioxide

Анотація

The results of studying the electrical conductivity σ for the glass-ceramic systems VO₂ ‒vanadium-phosphate glass (VPG) and VO2‒VPG‒SnO₂ with the additions of Cu and Cu₂O are presented. It is found that the jump of conductivity at the temperature of metal-semiconductor phase transition (MSPT) in VO₂ (T_t = 341K) takes place only for glass-ceramics containing not more than 5 wt% of these additives. When their content exceeds 5 wt%, the VO2 content decreases sharply according to the data of differential thermal analysis. The reason for this is the oxidation-reduction reactions in the liquid phase between Cu and VO₂ at ceramics synthesis. These reactions result in the appearance of Magneli phases in glass‒ceramics composition. The phase transitions in Magneli phases V₄O₇, V₅O₉, and V₆O₁₃ are indicated by the temperature dependence of σ, as bends of the straight lines in coordinates log10σ ~ 1/T at the phase
transition temperatures T_t of these phases: 240K, 150K, and 130K. The activation energy of σ for T> T_t is lower than for T <T_t, which indicates a change in the structure of energy zones inherent to MSPT.