First-principles simulation of high-pressure polymorphs in MgAl2O4
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We have used density functional theory to investigate the stability of MgAl2O4 polymorphs under pressure. Our results can reasonably explain the transition sequence of MgAl2O4 polymorphs observed in previous experiments. The spinel phase (stable at ambient conditions) dissociates into periclase and corundum at 14 GPa. With increasing pressure, a phase change from the two oxides to a calcium-ferrite phase occurs, and finally transforms to a calcium-titanate phase at 68 GPa. The calcium-titanate phase is stable up to at least 150 GPa, and we did not observe a stability field for a hexagonal phase or periclase + Rh2O3(II)-type Al2O3. The bulk moduli of the phases calculated in this study are in good agreement with those measured in high-pressure experiments. Our results differ from those of a previous study using similar methods. We attribute this inconsistency to an incomplete optimization of a cell shape and ionic positions at high pressures in the previous calculations.
KeywordsMgAl2O4 phases Ab initio calculations Phase transition Equation of state High pressure
The authors thank A. S. Côté for his valuable technical comments. This work made use of the UCL research computing facilities and of HPCx, the UK’s national high-performance computing service at the Daresbury Laboratory. This work was supported by NERC Computational Mineral Physics Consortium, UK and Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan.
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