Pressure‐Induced Phase Transition of B1 Oxides in Relation to Shock Compression Behavior of MnO

Shock compression measurements of MnO have been carried out up to 120 GPa, and a phase transition with a volume decrease, -ΔV/V 0 , of about 6 percent is observed at 90 f 3 GPa. Release adiabat measurements revealed that the high pressure phase was retained down to 37 GPa and the volume difference with respect to the rock salt (B1) phase was estimated to be about 23 percent. The observed large volume change in the phase transition of MnO excludes the possibility of the nickel arsenide (B8) structure for the high pressure phase, unlike the high pressure phase of Fe 1-x O. The cesium chloride (B2) structure is suggested to be a possible candidate from the systematics obtained for the B1-B2 transformation in alkaline earth monoxides, although the observed volume change would be too large. Furthermore, a possibility of change in the electronic configuration of transition metal ions at very high pressures, such as spin-pairing transition, is also inferred to assess the observed large volume change in MnO.