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/V0 of 0.509(1), corresponding to the pressure of 217+/-10 GPa. From the obtained pressure-volume data, the pressure derivative of the bulk modulus K0' 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 K0 obtained from previous ultrasonic experiments.