First-Principles Investigation of Electronic Properties and Phase Transition of Ti<sub>3</sub>O<sub>5</sub>
Stefan Jütten, Thomas Bredow
Abstract
Heat storage materials preserving large amounts of thermal energy over long time frames enable the storage of waste energy from thermal energy generation or excess energy generated by intermittent and renewable sources. Trititanium pentoxide, Ti3O5, has emerged as a promising material with a high energy storage density and the capability of releasing the stored energy on demand, for example, by the application of pressure. During the release, the higher energy λ polymorph undergoes an isostructural phase transition to the lower energy β polymorph. Accurate predictions of the heat storage properties of the two polymorphs using first-principles methods are not yet available. Using hybrid density functionals and the recently proposed r2SCAN meta-generalized gradient approximation functional augmented by the D3 dispersion correction, we offer a comprehensive description of the electronic ground state of this material. We find that r2SCAN-D3 provides a similar accuracy for structural and thermodynamic properties compared to hybrid functionals at an order of magnitude reduced computational cost. Inclusion of the dispersion interaction is essential to obtain correct energy differences between the two phases. The r2SCAN-D3 method is applied to the investigation of the reaction mechanism of the phase transition, resulting in full characterization of the transition state. We highlight the good performance of the r2SCAN-D3 functional by predicting the phase transition temperature and phase transition enthalpy of the heat storage system and recommend this method for high-throughput investigations of heat storage materials.