First-principles calculation of kinetic barriers and metastability for the corundum-to-Rh2O3(II) transition in Al2O3

摘要: We demonstrate that the rhombohedral corundum crystal and orthorhombic Rh2O3(II) are structurally related by a diffusionless monoclinic common subgroup pathway, along which intermediate structures have space group P 2/c symmetry. This transformation pathway is energetically favored because majority of Al?O bonds preserved during transition. Only 1/3 four-coordinated anions 1/2 six-coordinated cations break reform single bond. No other broken in transformation. Our calculated forward (corundum-to-Rh2O3(II)) enthalpy barrier (about 140?meV/atom) Al2O3 not pressure-sensitive at least up to 160?GPa, consistent with observed metastability phase around room temperature. In contrast, we predict significantly decreasing backward (Rh2O3(II)-to-corundum) on decompression, suggests high-pressure unlikely be recoverable ambient conditions. addition, propose general, subgroup-based approach compare elastic properties two phases different Bravais lattices. By treating both unit cells (non-primitive for phase), show very comparable those phase.