Phase Relations of Ni2In-Type and CaC2-Type Structures Relative to Fe2P-Type Structure of Titania at High Pressure: A Comparative Study

Density functional theory (DFT) based on first-principles calculations was used to study the high-pressure phase stability of various phases titanium dioxide (TiO2) at extreme pressures. We explored relations among following phases: experimentally identified nine-fold hexagonal Fe2P-type phase, previously predicted ten-fold tetragonal CaC2-type TiO2, and recently proposed eleven-fold Ni2In-type similar dioxides zirconia (ZrO2) hafnia (HfO2). Our calculations, using generalized gradient approximation (GGA), Fe2P → Ni2In transition occur 564 GPa CaC2 664 GPa. These transitions were deeply investigated with reference volume reduction, coordination number decrease, band gap narrowing better determine favorable post-Fe2P phase. Furthermore, it found that both are mostly driven by reduction across in comparison small contribution electronic energy gain. Additionally, our computed Birch–Murnaghan equation state for three reveals is densest while most compressible