Experimental study of the electronic and lattice contributions to the VO₂ transition

The contributions of electronic and crystallographic components to the semiconductor → metal transition in VO₂ have been estimated from resistivity, E.P.R., and calorimetric measurements of the electronic and thermodynamic properties of Ga_xV_-xO₂, where 0 < x < 0.0130. E.P.R. and resistivity measurements indicate a decrease in the metallic character of the high-temperature R phase with increasing x, and calorimetric measurements of the energetics of the transition show a decrease in the enthalpy and entropy of the transition with increasing levels of doping. This concomitant decrease in enthalpy and metallic character with increasing x implies a strong contribution of the electronic entropy to the transition. An extrapolation of the combined electronic and calorimetric data for Ga_xV _-xO₂ to pure VO₂ suggest that the electronic entropy comprises about 60% of the total entropy of transition in VO₂.