During past years, a number of reports have been published on synthesis of tetragonal allotrope of boron, t-B52 phase. However, no unambiguous characterization of the crystal structure has been performed to the present time, while remarkable variation of the a/c lattice-parameter ratio raises strong doubts about its uniqueness. Here the Rietveld refinement of the crystal structure of the high pressure - high temperature boron phase synthesized by a direct solid-state transformation of rhombohedral beta-B106 at 20 GPa and 2500 K has been reported for the first time. Although this boron allotrope belongs to the t-B52 type, its structure can be considered as pseudo-cubic with the a/c ratio of sqr(2).
@article{arxiv.1302.4236,
title = {Crystal structure of dense pseudo-cubic boron allotrope, pc-B52, by powder X-ray diffraction},
author = {Oleksandr O. Kurakevych and Vladimir L. Solozhenko},
journal= {arXiv preprint arXiv:1302.4236},
year = {2013}
}