The crystal structure of aluminum doped β-rhombohedral boron

A crystal structure of aluminum doped beta-rhombohedral boron was studied by single-crystal X-ray diffraction at 80 K. The crystals were synthesized using high-pressure high temperature technique at 3 GPa and 2100 K. The structure is based on three-dimensional framework made of B-12 icosahedra with voids occupied by the B-28-B-B-28 units, it has the R-3m space group with a = 10.9014(3), c = 23.7225(7) A lattice dimensions in hexagonal setting. Aluminum atoms are located in A1 and D special positions of the beta-B structure with occupancies of 82.7(6)% and 11.3(4)%, respectively. Additional boron atoms are located near the D-site. Their possible distribution is discussed. Finally we have found two appropriate structural models whose refinement suggests two possible chemical compositions, AlB44.8(5) and AlB37.8(5), which are in a good agreement with the chemical analysis data obtained from EDX. The crystal structure of AlB44.8(5) is described in detail. (c) 2012 Elsevier Inc. All rights reserved.