Prediction of an U2S3-type polymorph of Al 2O3 at 3.7 Mbar

Koichiro Umemoto, Renata M Wentzcovitch

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We predict by first principles a phase transition in alumina at ≈3.7 Mbar and room temperature from the CaIrO3-type polymorph to another with the U2S3-type structure. Because alumina is used as window material in shock-wave experiments, this transformation should be important for the analysis of shock data in this pressure range. Comparison of our results on all high-pressure phases of alumina with shock data suggests the presence of two phase transitions in shock experiments: the corundum to Rh 2O3(II)-type structure and the Rh2O 3(II)-type to CaIrO3-type structure. The transformation to the U2S3-type polymorph is in the pressure range reached in the mantle of recently discovered terrestrial exoplanets and suggests that the multi-megabar crystal chemistry of planetforming minerals might be related to that of the rare-earth sulfides.

Original languageEnglish (US)
Pages (from-to)6526-6530
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number18
StatePublished - May 6 2008


  • Alumina
  • First-principles calculation
  • High-pressure phase transition
  • Postperovskite
  • Rare-earth sulfide structure


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