Zone-axis x-ray diffraction of single-crystal Fe1-xO under pressure -: art. no. 174109

Zone-axis synchrotron x-ray diffraction of single-crystal Fe1-xO to 25 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. Fe1-xO 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 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 GPa.