Phase relations, thermal conductivity and elastic properties of ZrO2 and HfO2 polymorphs at high pressures and temperatures

Abstract

In the present study, P–T phase diagrams of ZrO₂ and HfO₂ for a wide pressure range of 0–150 GPa at 0–2500 K were calculated for the first time using density functional theory with the method of lattice dynamics within the quasi-harmonic approximation. We calculated P–T conditions for a full sequence of high-pressure transformations, P2₁/c → Pbca → Pnma → P2m, for both compounds. At low temperatures, these transformations for ZrO₂ are obtained at 7.6 GPa (P2₁/c → Pbca), 13.4 GPa (Pbca → Pnma), and 143 GPa (Pnma → P2m), while for HfO₂ similar polymorphic transitions are obtained at 9 GPa (P2₁/c → Pbca), 16 GPa (Pbca → Pnma), and 126 GPa (Pnma → P2m), correspondingly. At high temperatures, for both ZrO₂ and HfO₂ the P2₁/c and Pbca structures transform into the P4₂/nmc modification. In addition, the thermal conductivity and elastic properties of the ZrO₂ and HfO₂ polymorphs were calculated and compared with the available experimental and theoretical data.