In situ X-ray study of thermal expansion and phase transition of iron at multimegabar pressure

The density of epsilon-iron has been calculated at pressures and temperatur es up to 300 GPa and 1300 K, respectively. We observe epsilon to beta phase transition at pressures between 135 and 300 GPa and temperature above 1350 K; the pattern can be interpreted in terms of double hexagonal close-packe d structure. The density calculated at high pressure and temperature (330-3 60 GPa and 5000-7000 K) closely matches with preliminary reference Earth mo del density, thereby imposing constraint on the composition of the Earth's inner core.