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Unexpected Stable Phases of Tungsten Borides

Abstract

Tungsten borides are a unique class of compounds, with excellent mechanical properties comparable to traditional superhard materials. However, the in-depth understanding of these compounds is hindered by the uncertainty of their phase relations and complex crystal structures. Here, we explored the W-B system systematically by ab initio variable-composition evolutionary simulations at pressures from 0 to 40 GPa. Our calculations successfully found all known stable compounds and discovered two novel stable phases P-421m-WB, P21/m-W2B3, and three nearly stable R3m-W2B5, Ama2-W6B5, Pmmn-WB5 phases at ambient pressure and zero Kelvin. Interestingly, P-421m-WB is much harder than the known $\alpha$ and $\beta$ phases, while Pmmn-WB5 shows the highest hardness. Furthermore, it is revealed that the much debated WB4 becomes stable as P63/mmc (2 f.u. per unit cell) phase at pressures above \sim1 GPa, not at ambient pressure as reported previously. Our findings provide important insights for understanding the rich and complex crystal structures of tungsten borides, and indicate WB2, WB4, and WB5 as compounds with the most interesting mechanical properties.

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Publication details

The article was received on 04 Jul 2018, accepted on 07 Sep 2018 and first published on 07 Sep 2018


Article type: Paper
DOI: 10.1039/C8CP04222E
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    Unexpected Stable Phases of Tungsten Borides

    C. Zhao, Y. Duan, J. Gao, W. Liu, H. Dong, H. Dong, D. Zhang and A. R. Oganov, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP04222E

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