Structural and electronic evolution of Cr2O3 on compression to 55 GPa

Synchrotron single-crystal x-ray diffraction experiments have been performed on corundum-type Cr2O3 up to a pressure of 55 GPa in Ne and He pressure transmitting media. Diffraction experiments were complemented by measurements of optical absorption spectra with single crystal samples up to 60 GPa. Results of the diffraction data analysis rule out the earlier reported monoclinic distortion at 15–30 GPa, but indicate evidence of two discontinuous transitions of electronic or magnetic nature, most likely associated with a change in magnetic ordering and charge transfer. The compression mechanism established from single crystal refinements indicates much smaller distortion of the Cr3+ coordination environment than was previously assumed.

Graphical abstractNew synchrotron single-crystal x-ray diffraction experiments to 55 GPa in Ne and He complemented by measurements of optical absorption spectra show no indication of the earlier reported monoclinic distortion at 15–30 GPa, but indicate evidence of two discontinuous transitions of electronic or magnetic nature, most likely associated with a change in the magnetic ordering and charge transfer. The compression mechanism established from single crystal refinements indicates much smaller distortion of the Cr3+ coordination environment than was previously assumed.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► New data do not support earlier reported monoclinic distortion at 15 GPa. ► Polyhedral compressibility is 6.7% lower than the unit cell compressibility. ► Optical absorption indicates two color changes at 15 and 30 GPa. ► Optical changes are related to magnetic ordering and charge transfer transitions. ► A departure from the point charge model is detected above 30 GPa.