Crystal Structure, Stability, and Metal–Insulator–Metal Transitions in Tantalum Oxides: Implication for Memristive Devices

Tantalum oxide (TaOx) has been extensively explored as a promising material for memristive devices, but its atomic structures with different stoichiometries remain elusive. In this work, based on the particle-swarm optimization algorithm combined with density functional theory calculations, we systematically investigate the stoichiometry-dependent crystal structures, stability, and electronic properties of the TaOx family. We successfully identify new structures of TaOx with excellent dynamical, thermodynamic, and mechanical stability at ambient conditions, including Pbcn Ta2O3, P42/mnm TaO2, Pbam Ta2O5, and Pmm TaO3, which are energetically more favorable than those reported in the literature. Electronic structure calculations reveal that Ta2O3, TaO2, and TaO3 are metallic, while Ta2O5 exhibits insulating characteristics with a sizable band gap of 4.29 eV. Such metal–insulator–metal transitions with an increasing oxygen content in TaOx suggest the possible formation/breaking of conductive filaments in memristors. The fundamental origins underlying the electronic properties are analyzed. We expect these findings to provide insights into the atomic structures and electronic properties of technologically important oxides with significant potential for resistive random access memory, neuromorphic, and cognitive computing.