Hydrostatic-pressure dependence of the electronic properties of VO₂ near the semiconductor-metal transition temperature

Abstract

The hydrostatic-pressure dependence of the electronic properties of VO₂ near the semiconductor-metal transition to a pressure of 40 kbar is described. The temperature dependence of the VO₂ resistivity from 0°C through the semiconductor-metal transition temperature near 68°C to approximately 80°C at several pressures, and the pressure dependence of the resistivity at 26 and 74°C, are presented and discussed. It is shown that the transition temperature increases linearly with hydrostatic pressure at a rate of 0.082 ±0.005°C/kbar, in agreement with the measured volume change and latent heat at the transition, as determined from the Clausius-Clapeyron equation. This value is sample-independent within experimental error. Also, the conductivity activation energy in the semiconductor phase decreases linearly with hydrostatic pressure typically at a rate of between 1 and 2 mV/kbar, but varying significantly, depending on the sample. If the activated conductivity is due to an activated density of carriers, it is shown that, at a fixed temperature in the semiconductor phase, the carrier concentration must increase with pressure and the mobility must decrease with pressure. The results are compared with those expected on the basis of some of the published theories on semiconductor-metal transitions in solids.