Characteristic properties of metal–semiconductor phase transitions of vanadium dioxide in a polyethylene glycol medium containing tetraethylammonium bromide

A study has been made of samples of disperse vanadium dioxide (VO2) in a matrix of polyethylene glycol (M=1500) doped with tetraethylammonium bromide (TEABr). It has been established that under the influence of the dopant the heating of a sample up to the temperature of the metal-semiconductor phase transition (MSPT) results in a phase inhomogeneity of the sample: one portion of a disperse VO2 particle passes to the metallic state, while the other retains its semiconducting state. On the basis of the results of this study it is possible to conclude that small concentrations of TEA cations in a PEG matrix can exert a strong effect on the electronic structure of disperse VO2 particles. This is accompanied by the appearance of phase heterogeneity of VO2, which manifests itself in the fact that with the onset of MSPT with increasing temperature one portion of the substance passes to the metallic state, and the other remains in the semiconducting state. The heterogeneity of a sample is observed in the wide temperature interval 305<T<390 K. One of the probable causes of the observed phenomenon is a strong bonding of TEABr cations with the polymeric matrix, while bromine anions diffuse to the VO2 particle surface and discharge on it in the process of chemisorption. As a result, an electric field sets up, and the field lines are directed from cations localized in the polymer matrix to the VO2 particle surface.