Structural Phase Transitions in Aluminium above 320 GPa

With the application of pressure, a material decreases in volume as described in its equation of state, which is governed by energy considerations. At extreme pressures, common materials are thus expected to transform into new dense phases with extremely compact atomic arrangements that may also have unusual physical properties. For aluminium, first principle calculations have consistently predicted a phase transition sequence fcc–hcp–bcc in a pressure range below 0.5TPa [1–7]. The hcp phase was identified at 217GPa in an experiment (Akahama et al., 2006), and the bcc phase has been recently confirmed in a dynamic ramp-compression experiment coupled with time-resolved X-ray diffraction (Polsin et al. 2017). Here we confirm this observation with a synchrotron-based X-ray diffraction experiment carried out within a diamond-anvil cell and report indications of the onset of the transition towards a bcc structure at pressures beyond 320GPa. With this work, we also demonstrate the possibility of routine static high-pressure experiments with conventional bevelled diamond-anvil geometry in the 0.3–0.4TPa regime.