Static compression of wüstite (Fe0.98O) to 120 GPa

An X ray diffraction study on wüstite (Fe 0.98 O) was performed up to 120 GPa at room temperature and up to 160°C at 24 GPa using a diamond‐anvil‐type, high‐pressure apparatus. Wüstite transforms from the cubic rock salt structure into a distorted structure with a rhombohedral unit cell at about 16 GPa at room temperature, and retrogressive transition occurs when the distorted phase is heated to 160°C at 24 GPa. This transition can be explained as the paramagnetic to antiferromagnetic transition resulting from the increase of the Néel temperature of wüstite under high pressure. No further discontinuous change in the X ray diffraction pattern was observed up to 120 GPa at room temperature. This result is in disagreement with shock compression experiments, which have indicated the existence of a large discontinuous volume decrease at approximately 70 GPa.