title: Polymorphs of Alumina Predicted by First Principles: Putting Pressure on the Ruby Pressure Scale
abstract: Fully optimized quantum mechanical calculations indicate that Al2O3 transforms from the corundum structure to the as yet unobserved Rh2O3 (II) structure at about 78 gigapascals, and it further transforms to Pbnm-perovskite structure at 223 gigapascals. The predicted x-ray spectrum of the Rh2O3 (II) structure is similar to that of the corundum structure, suggesting that the Rh2O3 (II) structure could go undetected in high-pressure x-ray measurements. It is therefore possible that the ruby (Cr3+-doped corundum) fluorescence pressure scale is sensitive to the thermal history of the ruby chips in a given experiment.
authors.affiliation: K. T. Thomson, Department of Chemical Engineering and Materials Science, and Minnesota Supercomputer Institute, University of Minnesota, Minneapolis, MN 55455, USA. R. M. Wentzcovitch, Department of Chemical Engineering and Materials Science, and Minnesota Supercomputer Institute, University of Minnesota, Minneapolis, MN 55455, USA, and Instituto de Fisica, Universidade de Sao Paulo, CP 66318, 0 5389-970, Sao Paulo, SP, Brazil. M. S. T. Bukowinski, Department of Geology and Geophysics, University of California, Berkeley, CA 94720, USA.
authors.initials: KT
authors.lastname: Thomson
authors.initials: RM
authors.lastname: Wentzcovitch
authors.initials: MST
authors.lastname: Bukowinski