Boron oxides under pressure: Prediction of the hardest oxides

We search for stable compounds of boron and oxygen at pressures from 0 to 500 GPa using the ab initio evolutionary algorithm uspex. Only two stable stoichiometries of boron oxides, namely, B6O and B2O3, are found to be stable, in good agreement with experiment. A hitherto unknown phase of B6O at amb...

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Bibliographic Details
Published in:Physical review. B 2018-11, Vol.98 (17), p.174109, Article 174109
Main Authors: Dong, Huafeng, Oganov, Artem R., Brazhkin, Vadim V., Wang, Qinggao, Zhang, Jin, Davari Esfahani, M. Mahdi, Zhou, Xiang-Feng, Wu, Fugen, Zhu, Qiang
Format: Article
Language:English
Subjects:
Atomic properties
Boron
Boron compounds
Boron oxides
Boron suboxide
Coordination numbers
Evolutionary algorithms
Predictions
Pressure
Silicon dioxide
Stishovite
Stoichiometry
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Summary:We search for stable compounds of boron and oxygen at pressures from 0 to 500 GPa using the ab initio evolutionary algorithm uspex. Only two stable stoichiometries of boron oxides, namely, B6O and B2O3, are found to be stable, in good agreement with experiment. A hitherto unknown phase of B6O at ambient pressure, Cmcm−B6O, has recently been predicted by us and observed experimentally. For B2O3, we predict three previously unknown stable high-pressure phases-two of these (Cmc21 and P212121) are dynamically and mechanically stable at ambient pressure, and should be quenchable to ambient conditions. Their predicted hardnesses, reaching 33–35 GPa, make them harder than SiO2-stishovite. These are the hardest known oxides (if one disregards B6O, which is essentially a boron-based insertion compound). Under pressure, the coordination number of boron atoms changes from 3 to 4 to 6, skipping fivefold coordination.
ISSN:2469-9950
2469-9969
DOI:10.1103/PhysRevB.98.174109