Equation of state ofα-Al2O3

The ambient temperature equation of state of ruby in the corundum phase ($\ensuremath{\alpha}$-Al${}_{2}$O${}_{3}$) has been measured up to 165 GPa in a diamond anvil cell, using a soft pressure transmitting medium. No clear sign of phase transformation or amorphization has been observed in this range, which could affect its luminescence signal. The equation of state of $\ensuremath{\alpha}$-Al${}_{2}$O${}_{3}$ has also been calculated within density functional theory, with two different approximations of the exchange-correlation energy (local density and generalized gradient). With suitable correction, these equations of state are predictive within $\ensuremath{\Delta}P/P=2.5%$.