Inverse versus Normal NiAs Structure as High-Pressure Phase of FeO and MnO

TL;DR

This study uses first principles calculations to predict the high-pressure phases of FeO and MnO, revealing distinct structural and electronic properties with implications for Earth's core.

Contribution

It introduces the prediction of inverse B8 structure for FeO and normal B8 for MnO under high pressure, highlighting FeO's insulating nature in this phase.

Findings

MnO adopts a metallic nB8 structure at high pressure.

FeO's high-pressure phase is an insulating inverse B8 structure.

X-ray data supports the theoretical predictions.

Abstract

The high-pressure phases of FeO and MnO were studied by the first principles calculations. The present theoretical study predicts that the high-pressure phase of MnO is a metallic normal B8 structure (nB8), while that of FeO should take the inverse B8 structure (iB8). The novel feature of the unique high-pressure phase of stoichiometric FeO is that the system should be a band insulator in the ordered antiferromagnetic (AF) state and that the existence of a band gap leads to special stability of the phase. The observed metallicity of the high-pressure and high-temperature phase of FeO may be caused by the loss of AF order and also by the itinerant carriers created by non-stoichiometry. Analysis of x-ray diffraction experiments provides a further support to the present theoretical prediction for both FeO and MnO. Strong stability of the high-pressure phase of FeO will imply possible important roles in Earth's core.