title: Prediction of new thermodynamically stable aluminum oxides.
abstract: Recently, it has been shown that under pressure, unexpected and counterintuitive chemical compounds become stable. Laser shock experiments (A. Rode, unpublished) on alumina (Al2O3) have shown non-equilibrium decomposition of alumina with the formation of free Al and a mysterious transparent phase. Inspired by these observations, we have explored the possibility of the formation of new chemical compounds in the system Al-O. Using the variable-composition structure prediction algorithm USPEX, in addition to the well-known Al2O3, we have found two extraordinary compounds Al4O7 and AlO2 to be thermodynamically stable in the pressure ranges 330-443 GPa and above 332 GPa, respectively. Both of these compounds at the same time contain oxide O(2-) and peroxide O2(2-) ions, and both are insulating. Peroxo-groups are responsible for gap states, which significantly reduce the electronic band gap of both Al4O7 and AlO2.
authors.affiliation: Department of Geosciences, State University of New York, Stony Brook, NY 11794, USA.
authors.forename: Yue
authors.initials: Y
authors.lastname: Liu
authors.affiliation: 1] Department of Geosciences, State University of New York, Stony Brook, NY 11794, USA [2] Moscow Institution of Physics and Technology, 9 Institutskiy Lane, Dolgoprudny City, Moscow Region 141700, Russia [3] School of Materials Science, Northwestern Polytechnical University, Xi'an 710072, China.
authors.forename: Artem R
authors.initials: AR
authors.lastname: Oganov
authors.affiliation: Department of Geosciences, State University of New York, Stony Brook, NY 11794, USA.
authors.forename: Shengnan
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Geosciences, State University of New York, Stony Brook, NY 11794, USA.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Zhu
authors.affiliation: 1] Department of Geosciences, State University of New York, Stony Brook, NY 11794, USA [2] School of Physics and MOE Key Laboratory of Weak-Light Nonlinear Photonics, Nankai University, Tianjin 300071, China.
authors.forename: Xiao
authors.initials: X
authors.lastname: Dong
authors.affiliation: University of Vienna, Faculty of Physics and Center for Computational Materials Science, Sensengasse 8/12, A-1090 Wien, Austria.
authors.forename: Georg
authors.initials: G
authors.lastname: Kresse
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