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 ma trix of polyethylene glycol (M = 1500) doped with tetrathylammonium bromide (TEABr). It has been established that under the influence of the dopant th e heating of a sample up to the temperature of the metal-semiconductor phas e transition (MSPT) results in a phase inhomogeneity of the sample: one por tion of a disperse VO2 particle passes to the metallic state, while the oth er retains its semiconducting state. On the basis of the results of this st udy 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 dispe rse VO2 particles. This is accompanied by the appearance of phase heterogen eity 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 met allic state, and the other remains in the semiconducting state. The heterog eneity of a sample is observed in the wide temperature interval 305 < T< 39 0 K. One of the probable causes of the observed phenomenon is a strong bond ing of TEABr cations with the polymeric matrix, while bromine anions diffus e to the VO2 particle surface and discharge on it in the process of chemiso rption. As a result, an electric field sets up, and the field lines are dir ected from cations localized in the polymer matrix to the VO2 particle surf ace. (C) 2001 Elsevier Science B.V. All rights reserved.