Polymorphic transitions of diborane at sub- and near-megabar pressures.

Amin Torabi,Viktor N Staroverov,Chitra Murli,Yang Song

doi:10.1038/srep13929

Amin Torabi, Viktor N Staroverov + Show 2 more

Open Access

https://doi.org/10.1038/srep13929

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Abstract

Recent theoretical investigations of high-pressure structures of diborane have yielded many intriguing predictions which have so far remained untested due to challenges of acquiring experimental data at extreme pressures. Here we report new pressure-induced polymorphic transformations of crystalline diborane observed between 36 and 88 GPa by in situ Raman spectroscopy and interpreted using electronic structure calculations. Two previously unknown phase transitions are identified near 42 and 57 GPa, as evidenced by significant changes in the Raman profiles. The corresponding new phases, labeled IV and V, consist of B2H6 molecules and have triclinic unit cells (P), as deduced through evolutionary structure search and comparison of experimental and simulated Raman spectra. Density-functional calculations suggest that, at pressures above 110 GPa, phase V will form new molecular structures consisting of one-dimensional (BH3)n chains and will become metallic near 138 GPa. Our findings make a significant contribution to the elucidation of the structures and properties of diborane in the near-megabar pressure region.

Highlights

IntroductionNo direct evidence of non-dimer-based phases of boron hydride has been obtained to date due to experimental challenges in both sample confinement and in situ structural characterization under extreme pressures
Despite these theoretical predictions, no direct evidence of non-dimer-based phases of boron hydride has been obtained to date due to experimental challenges in both sample confinement and in situ structural characterization under extreme pressures
At the starting pressure of 36 GPa, we deal with the known phase III (P21/c)[15], as evidenced by the fact that the experimental Raman profile of the sample at 36 GPa is best reproduced by the simulated Raman spectrum of phase III for the same pressure

Summary

Introduction

No direct evidence of non-dimer-based phases of boron hydride has been obtained to date due to experimental challenges in both sample confinement and in situ structural characterization under extreme pressures. Our interpretation of the experimental data using electronic structure calculations suggests that B2H6 molecular units persist beyond 100 GPa, but transform into one-dimensional (BH3)n chains near 110 GPa, and that the latter polymorph becomes metallic at even higher pressures. These findings shed light on the previously unknown high-pressure structures of diborane and take us one step closer to solving the problem of hydrogen metallization

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