Stability of 12CaO•7Al2O3 Crystal under High-Pressure: Experimental and First-Principles Approaches

Stability of 12CaO center dot 7Al(2)O(3) (C12A7) crystal under high-pressure conditions is investigated by sample recovery experiments and first-principles calculations. After high-pressure and high-temperature treatments, C12A7 crystal is mainly decomposed to 2CaO center dot Al2O3 (C2A) and 4CaO center dot 3Al(2)O(3) (C4A3). According to first-principles calculations, the volume of C12A7 crystal is larger than that of [4(C2A)+C4A3]. From energetic point of view, C12A7 is stable at 0 GPa but it becomes unstable as pressure increases. This is caused by large volume of C12A7 at 0 GPa while the contribution of volume shrink of each substance is rather small. This indicated that the volume at 0 GPa is a dominant factor in these systems under high-pressure.