Crystal structure of dense pseudo-cubic boron allotrope, pc-B52, by powder X-ray diffraction

TL;DR

This study reports the first detailed crystal structure analysis of a dense pseudo-cubic boron allotrope, pc-B52, synthesized under high pressure and temperature, clarifying its structure and relation to tetragonal boron phases.

Contribution

It provides the first Rietveld refinement of the high-pressure, high-temperature boron phase, revealing its pseudo-cubic structure and resolving previous ambiguities about its crystal parameters.

Findings

First crystal structure refinement of dense pc-B52 boron allotrope

Identification of pseudo-cubic structure with a/c ratio of √2

Clarification of structural differences from tetragonal boron phases

Abstract

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).