Study of the phase transformations and equation of state of magnesium by synchrotron x-ray diffraction

Abstract

We studied the phase behaviour and the P – V – T equation of state of Mg by in situ energy-dispersive x-ray diffraction in a multi-anvil apparatus in the pressure–temperature range up to 18.6 GPa and 1527 K. At high temperatures, an hcp to dhcp transition was found above 9.6 GPa, which differs from the hcp to bcc transformation predicted by theoretical calculations. At room temperature, the hcp phase remains stable within the pressure range of this study with an axial ratio, c/a, close to the ideal. The melting of Mg was determined at 2.2, 10 and 12 GPa; the detected melting temperatures are in good agreement with previous diamond anvil cell results. The P – V – T equation of state determined based on the data of this study gives B0 = (36.8 ± 3) GPa, B0 ' = 4.3 ± 0.4, α0 = 25 × 10−6 K−1, ∂α/∂T = (2.3 ± 0.2) × 10−7 K−2 and ∂B0,T /∂T = (−2.08 ± 0.09) × 10−2 GPa K−1.