Dielectric Spectroscopy of Strongly Correlated Electronic States of Vanadium Dioxide

Abstract

The thermal evolution of the conductivity of a VO₂ film and database-obtained band gap E_g of film nanocrystallites is traced in the temperature range of –196°C < T < 100°C (77 K < T < 273 K); the level position of donor impurity centers is determined to be E_d = 0.04 eV. It is shown that energy E_g decreases from 0.8 to ∼0 eV with an increase in temperature in the range of 273 K < T < 300 K, which is caused by the narrowing of the energy gap due to correlation effects and considered as the temperature-extended Mott “insulator–metal” electron phase transition with the monoclinic lattice symmetry retained. The subsequent jump in the symmetry from monoclinic to tetragonal with a further increase in temperature is considered as the Peierls structural phase transition, the temperature of which is in the vicinity of 340 K and determined by the size effects, nonstoichiometry of VO₂ film nanocrystallites, and degree of their adhesion to the substrate.