Crystal Structure,\nStability, and Metal–Insulator–Metal\nTransitions in Tantalum Oxides: Implication for Memristive Devices

Tantalum oxide (TaO<i><sub>x</sub></i>) has\nbeen extensively\nexplored as a promising material for memristive devices, but its atomic\nstructures with different stoichiometries remain elusive. In this\nwork, based on the particle-swarm optimization algorithm combined\nwith density functional theory calculations, we systematically investigate\nthe stoichiometry-dependent crystal structures, stability, and electronic\nproperties of the TaO<i><sub>x</sub></i> family. We successfully\nidentify new structures of TaO<i><sub>x</sub></i> with excellent\ndynamical, thermodynamic, and mechanical stability at ambient conditions,\nincluding <i>Pbcn</i> Ta<sub>2</sub>O<sub>3</sub>, <i>P</i>4<sub>2</sub><i>/mnm</i> TaO<sub>2</sub>, <i>Pbam</i> Ta<sub>2</sub>O<sub>5</sub>, and <i>Pmm</i> TaO<sub>3</sub>, which are energetically more favorable than those\nreported in the literature. Electronic structure calculations reveal\nthat Ta<sub>2</sub>O<sub>3</sub>, TaO<sub>2</sub>, and TaO<sub>3</sub> are metallic, while Ta<sub>2</sub>O<sub>5</sub> exhibits insulating\ncharacteristics with a sizable band gap of 4.29 eV. Such metal–insulator–metal\ntransitions with an increasing oxygen content in TaO<i><sub>x</sub></i> suggest the possible formation/breaking of conductive filaments\nin memristors. The fundamental origins underlying the electronic properties\nare analyzed. We expect these findings to provide insights into the\natomic structures and electronic properties of technologically important\noxides with significant potential for resistive random access memory,\nneuromorphic, and cognitive computing.