Phase Transition in VO₂

The thermal dilatation of VO 2 has been measured on ceramic samples from room temperature to 95°C, in connection with Mott's consideration which interpretes the non-metal to metal transition observed in some transition metal oxides as an effect of contraction of lattice spacings. A discontinuous volume expansion was unexpectedly observed at 65°C with increasing temperature. The magnetic susceptibility has also been measured in the vicinity of the transition point. Below the transition point it has a temperature indenpendent value and at the transition point it makes a stepwise increase, but no singular peak was observed there. A measurement of the temperature dependence of the specific heat was carried out by an adiabatic type calorimeter. A distinct anomaly was observed near the transition point and the transition heat was estimated as about 750 cal/mol. These data suggest that the transition would be of the fist kind.