Phase transition and high-pressure behavior of divalent metal oxides

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Abstract
The phase transition, relative stability, and high-pressure elastic behavior of alkaline-earth and transition-metal oxides have been successfully predicted by means of two well-known model potentials developed by Sangster and Stoneham and by Mackrodt and Stewart. The phase-transition pressures for these oxides are predicted to lie in the range 85 to 202 GPa. The relative volume changes corresponding to these transition pressures occur from 3.3% to 6.5%. Our results for transition pressures are higher than the available experimental data. However, the transition pressure from B1 to B2 structures increases with decreasing cation–to–anion-radii ratio at least qualitatively as the trend shown by the current data available for some of these oxides. The variation of elastic constants with pressure predicted from these models followed the same trend as that revealed by modified-electron-gas-model theory. The ratio of shear-to-bulk modulus at the predicted transition pressure for these oxides lies between 0.06 to 0.22. The discrepancies between theoretical and experimental results have been ascribed to the many-body interactions which are significantly important in ionic crystals.