Abstract
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 (Tt = 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 Tt of these phases: 240K, 150K, and 130K. The activation energy of σ for T> Tt is lower than for T <Tt, which indicates a change in the structure of energy zones inherent to MSPT.
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