Activation diffusion of oxygen under conditions of the metal-semiconductor phase transition in vanadium dioxide

Density functional theory is used to calculate the energies of formation of oxygen vacancies and migration of oxygen in the monoclinic and rutile phases of vanadium dioxide. The results are compared to estimates of the parameters of activation diffusion of oxygen using data from the electron-beam modification of thin film structures of vanadium dioxide and their subsequent reduction in the temperature range of 20–100°C. It is shown that diffusion in both phases of vanadium dioxide has a preferential direction of oxygen migration along axis а in the monoclinic phase and axis с in the rutile phase. The difference between the rate of oxygen vacancy generation upon electron-beam exposure above and below the temperature of metal–semiconductor phase transition is explained by the jump (~150%) in the activation energy of oxygen diffusion upon the structural transition of rutile–monoclinic phase. The mobility of oxygen (oxygen vacancies) correspondingly changes by more than an order of magnitude.