The crystal structure of aluminum doped β-rhombohedral boron

A crystal structure of aluminum doped β-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 B12 icosahedra with voids occupied by the B28–B–B28 units, it has the R-3m space group with a=10.9014(3), c=23.7225(7) Å lattice dimensions in hexagonal setting. Aluminum atoms are located in A1 and D special positions of the β-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.

The atomic distribution near the B(15) atom (non-labeled atom in the center of the picture) shown along the c axis. Anisotropic displacement ellipses for Al(2) (D-site) and B(15) are shown with 50 % probability level. The mirror plane with Miller indices (1 1 0) and related to it (−1 2 0) and (−2 1 0) generated by the 3-fold rotation-inversion axis parallel to the c axis splits the position of B(16) over two sites.Figure optionsDownload as PowerPoint slideHighlights
► The crystal structure of the AlB44.8(5) has been refined.
► Aluminum atoms partially fill certain types of voids (the A1- and D-sites).
► We have got two possible models of atomic distribution near the D-site.