Phase composition, microstructure and conductivity of (85-α)VO2–15(Vanadium–Phosphate–Glass)–αCu glass–ceramics

Electric conductivity, microstructure and phase composition of (85-α)VO2–15VPG–αCu glass–ceramics (VPG = Vanadium–Phosphate–Glass) with copper content in the interval 0 wt% ⩽ α ⩽ 15 wt% were investigated. VPG is the glass (molar %) 80V2O5–20P2O5. Only two phases: VO2 and VPG were identified when α ⩽ 5 wt%. VO2 crystallites, VPG and pores are observed in these ceramic microstructures. Glass forms layers 1–2 μm thick in the space between VO2 crystallites. The copper is dissolved in VPG during glass–ceramic synthesis. It increases the electric conductivity of the glass and provides improvement of electrical bonds between VO2 crystallites. Therefore glass–ceramics conductivity exhibits an abrupt change of approximately 100× in the vicinity of the phase transition temperature, Tt, in VO2. A new crystalline phase appears in (85-α)VO2–15VPG–αCu ceramics when α ∼ 6 wt%. This phase is observed as small crystallites with the sizes of 1–5 μm. The increase in such phase content, with an increase in copper content is accompanied by a decrease in the content of VO2. Percolation along the new phase is a primary contributor to electric conductivity when α ⩾ 8 wt%. In this case the conductivity exhibits no abrupt change in the vicinity of the temperature Tt. The new phase is probably the bronze CuxV2O4. It crystallizes from a liquid phase during glass–ceramics synthesis.