Zone-axis synchrotron x-ray diffraction of single-crystal ${\mathrm{Fe}}_{1-x}\mathrm{O}$ to $25\mathrm{GPa}$ is used to study the effect of pressure on the defect cluster superstructure and to obtain further details on the cubic-to-rhombohedral phase transition in this material. ${\mathrm{Fe}}_{1-x}\mathrm{O}$ is found to exhibit a pressure-induced long-range order-disorder transition of defect clusters as the satellite reflections originating from an incommensurate defect superstructure disappear around $14.0\mathrm{GPa}$. The wave vectors of the incommensurately modulated defect structure increase with pressure, while the intensity of incommensurate peaks decreases. In contrast to temperature-induced order-disorder transitions, the pressure-induced transition is not reversible. Additionally, twinning is unambiguously observed to accompany the transition from a cubic to a rhombohedral phase at $19.8\mathrm{GPa}$.

• Received 25 March 2005

DOI:https://doi.org/10.1103/PhysRevB.72.174109