INVERSE VERSUS NORMAL NIAS STRUCTURES AS HIGH-PRESSURE PHASES OF FEO AND MNO

The phase stability of FeO and MnO under high pressure was studied wit h the first-principles calculations. Our results predict that the high -pressure phase of MnO is a metallic normal NiAs (B8) structure, while that of FeO is the inverse B8 structure (iB8). No materials have ever been known to take the iB8 structure. The novel feature of the iB8 Fe O is that the system should be a band insulator in the antiferromagnet ic state. Analysis of x-ray diffraction experiments provides further s upport to the present theoretical prediction for both FeO and MnO.