Powder X-ray diffraction study on possible structural change around 550 K in β-rhombohedral boron

Abstract

In this study, to investigate the possible structural change at ~550 K, the temperature dependence of powder X-ray diffraction (XRD) patterns of β-rhombohedral boron for a wide temperature range between 270 and 873 K was measured. We indexed all powder XRD patterns as β-rhombohedral boron for a whole temperature range; however, we observed that, at >550 K, the temperature dependence of the lattice parameters changed their slope. Moreover, at a temperature >600 K, we observed a drastically structural and local B12 icosahedral cluster-volume change, i.e., each icosahedral cluster-volume started to shrink and expand. Both shrinking and expansion depended on the electron deficiency and excess of B12 clusters, respectively. Moreover, the void volume started increasing at the same temperature range. Additionally, the B13 site occupancy and the total number of boron atoms at the interstitial site (B16–B20 site) showed significant temperature dependence. Therefore, our observation is an experimental validation of the interatomic hopping of boron above 550 K predicted by Hoffmann and Werheit [S. Hoffmann and H. Werheit, Solid State Sciences 14, 1572 (2012)].