Polaron-Induced Metal-to-Insulator Transition in Vanadium Oxides from Density Functional Theory Calculations

Vanadium oxides have been extensively studied as phase-change memory units in artificial synapses for neuromorphic computing due to their metal-insulator transitions (MIT) at or near room temperature. Recently, injection of charge carriers into vanadium oxides, e.g., via optically via a heterostructure, has been proposed as an alternative switching mechanism and also potentially as a means to tune the MIT temperature. In this study, we explore the formation of small polarons in the low temperature (LT) insulating phases for V3O5,VO2, and V2O3, and the barriers to their migration using density functional theory calculations. We find that V3O5 exhibits very low hole and electron polaron migration barriers ({$<$}100 meV) compared to V2O3 and VO2, leading to much higher estimated polaronic conductivity. We also link the relative migration barriers to the amount of distortion that has to travel when the polaron migrate from one site to another. Polarons in V3O5 also have smaller binding energies to vanadium and oxygen vacancy defects. These results suggest that the triggering of the MIT via injection of charge carriers are due to the formation of small polarons that can migrate rapidly through the crystal.