A New Discovery Answers an Old Question

February 20, 2012

The transition-metal monoxide FeO is an archetypal example of a Mott insulator—a material that should conduct electricity under conventional band theories but becomes an insulator when measured, especially at low temperatures, and a major iron-bearing component of the Earth’s interior. Understanding the high-pressure behavior of this material is important for both solid-state physics and Earth science. Despite considerable study over the past 30 years, the origin of the high-pressure-induced cubic-rhombohedral ferroic transition in FeO, which is a distortion of the original cubic structure to that of a rhomboid shape, has not been well understood.

Now the first imaging of non-reflection domain wall structures forming in the ferroic transition of the ferrous oxide Fe0.94O has been reported by researchers utilizing the U.S. Department of Energy Office of Science’s Advanced Photon Source (APS) at Argonne National Laboratory. The results revealed a non-reflection type of domain wall structure forming due to the so-called “cubic-rhombohedral transition,” where the crystal structure of the material changes from cubic to rhomboidal. This discovery suggests the cubic-rhomboid transition could be associated with defects in the material and is unlikely to be caused by ferroelasticity, in which a material may develop a spontaneous strain, as predicated by previous research.

The surprising impact of defects on structural stability discovered by this study not only brings a new understanding of the origin of the cubic-rhomboid transition, but also underscores the need for a greater understanding of how defects in a material influence electronic and thermoelastic properties at high pressure, which has almost never been taken into consideration in previous high-pressure studies of materials.

Yang Ding et al., Appl. Phys.Lett. 100, 041903 (2012). DOI: 10.1063/1.3679117