Crystal structure of dense pseudo-cubic boron allotrope, pc-B_(52), by powder X-ray diffraction

摘要

During past years, a number of reports have been published on synthesis of tetragonal allotrope of boron, t-B_(52) 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 β-B_(106) at 20 GPa and 2500 K has been reported for the first time. Although this boron allotrope belongs to the t-B_(52) type, its structure can be consideredas pseudo-cubic with the a/c ratio of 2~(1/2).