The Displacive Phase Transition of Vanadium Dioxide and the Effect of Doping with Tungsten

Static-lattice calculations have been employed to model the phases of VO 2 and V 1−δ W δ O 2 . Interatomic potentials were empirically fitted to reproduce the low- and high-temperature phases (monoclinic and tetragonal, respectively) of vanadium dioxide as well as the monoclinic phase of tungsten dioxide. For pure VO 2, we located the soft modes of the high-temperature phase, which characterize the initial atomic displacements that lead to the displacive phase transition to the low-temperature phase. The T = 0 structure of the saddle point, where only half of the one-dimensional chains have undergone Peierls distortions, and the ionic motion along the lowest-energy path for the phase transition are described. For V 1−δ W δ O 2, we found that doping significantly stabilizes the high-temperature phase relative to the low-temperature phase, which explains the observed depression in the transition temperature as δ increases. For the high- and low-temperature phases, the local structures about the dopant, which were obtained by employing a Mott−Littleton approach, resembled those of the low- and high-temperature phases, respectively.