Evidence of a fcc-hcp Transition in Aluminum at Multimegabar Pressure

The structure phase transition and the equation of state (EOS) of the third-period simple metal Al were investigated at pressure up to 333 GPa by powder x-ray diffraction experiments. The theoretically predicted fcc-hcp transition was observed at the reduced volume $V/{V}_{0}$ of 0.509(1), corresponding to the pressure of $217\ifmmode\pm\else\textpm\fi{}10\text{ }\text{ }\mathrm{GPa}$. From the obtained pressure-volume data, the pressure derivative of the bulk modulus $K_{0}{}^{\ensuremath{'}}$ for the EOS of fcc-Al was determined to be 4.83(3) by fitting to the Vinet formulation with a fixed value 72.7 GPa of ${K}_{0}$ obtained from previous ultrasonic experiments.