Phase transition behaviour of VO2

In order to study the effect of preparative conditions on the phase behaviour, polycrystalline VO2 samples were synthesized from V2O5 and V2O3 using three methods. Heat capacities were measured in the temperature range 288 to 373 K during both heating and cooling cycles. The heating cycle showed a twin heat capacity peak, which is reproducible. During the cooling cycle different hysteresis effects were observed. The assumption of the simultaneous coexistence of two similar phases of VO2 at RT gives rise to the two transitions in the heat capacity curve. No evidence for the presence of a second phase could be found from X-ray diffraction data