High pressure synthesis and investigation of single crystals of metastable boron phases

AbstractIn the present work we have confirmed the existence of the tetragonal boron phase T-50 that was disputed for more than a half of a century. This phase was reproducibly synthesized at high pressures and high temperatures (HPHT) in the form of single crystals and its structure was refined based on single-crystal synchrotron X-ray diffraction data. We also present here a previously unknown rhombohedral boron phase synthesized in a limited HPHT field. Its structure was solved based on in house single-crystal X-ray diffraction data and found to be similar to that of boron carbide. After hitherto known stable α-B, β-B, and γ-B polymorphs, T-50 and the newly obtained rhombohedral boron phases were designated in the present work as δ-B and ϵ-B, correspondingly. From the experimental evidences, both the phases are considered as metastable.Keywords: boron polymorphstetragonal boronmetastable boron phasesnew boron phasesingle-crystal synthesispressure temperature phase diagram of boron AcknowledgementsThe work was supported by the German Research Foundation (DFG) through the DFG Priority Program 1236. This program was funded by the Deutsche Forschungsgemeinschaft from 2006 to 2013. ND thanks DFG for the financial support through the Heisenberg Program. The help of Y. Filinchuk, D. Chernyshov, and V. Dmitriev in the synchrotron X-ray diffraction data collection is gratefully acknowledged.Notes†This contribution is part of the final report summarizing the results of the DFG-priority project SPP1236, which was funded by the Deutsche Forschungsgemeinschaft from 2006–2013.