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 GaxV−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 GaxV−xO2 to pure VO2 suggest that the electronic entropy comprises about 60% of the total entropy of transition in VO2.