Prediction of a Reentrant Phase Transition Behavior of Cotunnite in Zirconia and Hafnia at High Pressures

• Published in: Journal of superhard materials 2023-02, Vol.45 (1), p.10-19
• Main Authors: Al-Khatatbeh, Yahya, Tarawneh, Khaldoun, Alsaad, Ahmad M.
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Density functional theory; Enthalpy; First principles; Hafnium oxide; High pressure; Mathematical analysis; Phase transitions; Physical Chemistry; Production; Properties; Structure; Zirconium dioxide
• ISSN: 1063-4576; 1934-9408
• DOI: 10.3103/S1063457623010021

First-principles calculations within the framework of density-functional theory (DFT) are implemented to investigate the high-pressure behavior of ultrahigh high-pressure phases of zirconia (ZrO 2 ) and hafnia (HfO 2 ) compounds. We have studied the phase relations among the highest-pressure phases of these dioxides: The previously observed OII (cotunnite) phase, Fe 2 P-type phase, and the recently predicted Ni 2 In-type phase. Our calculations, using the generalized gradient approximation (GGA), predict unusual phase transition of OII phase with respect to Fe 2 P phase. In both dioxides, our enthalpy calculations show that OII phase transforms to Fe 2 P phase at 96 GPa (122 GPa) for ZrO 2 (HfO 2 ), where Fe 2 P phase remains stable up to 254 GPa (310 GPa) in ZrO 2 (HfO 2 ) before it transforms back to OII phase, indicating a reentrant transition behavior of OII phase. Our calculations show that OII → Fe 2 P and Fe 2 P → OII transitions are associated with a slight change in both volume and enthalpy. Consequently, we have concluded that the transition to Ni 2 In phase likely occurs from OII phase rather than Fe 2 P phase, and thus we provide an updated high-pressure phase transition sequence for zirconia and hafnia at such extreme pressures. The OII → Ni 2 In transition is predicted to occur at 302 and 372 GPa in zirconia and hafnia, respectively. Furthermore, to obtain a deeper insight into the mechanism of the phase transitions in ZrO 2 and HfO 2 , the effect of the components of the enthalpy difference across our predicted phase transitions has been thoroughly investigated.