Influence of a high conductivity additive on the electrical properties of vanadium dioxide-based ceramics

The influence of copper additive on the electrical resistivity, ρ, and the value of the resistivity jump, ρs/ρm, in the vicinity of the phase transition temperature Tt≈68 °C) has been studied for ceramics of composition (wt.%): xCu–(85−x) VO2 –15VPG (where VPG—vanadium phosphate glass of composition (mol%) 80V2O5–20P2O5). For higher x values, the density of the ceramics increases, and the magnitudes of ρ and ρs/ρm decrease. The increasing density is associated with the decreasing porosity of the ceramics. To explain the ρ and ρs/ρm behaviour with variation of x, the percolation theory was used. The percolation of electrical current occurs through the copper and the electrical properties of the ceramics are determined by the additive copper at x⩾8 wt.%. At x<8 wt.%, the basic contribution to the electrical conductivity of the ceramics is given by VO2. Vanadium dioxide based ceramics with content of copper in the range 5–8 wt.% have a resistivity jump ρs/ρm of not less than one order and have more stable behaviour in their electrical parameters after thermocycling through temperature Tt, than do ceramics without copper.