The crystal structure of a simple rhombohedral form of boron

Abstract

A new modification of boron, resulting from the pyrolytic decomposition of BI z on a heated surface (800 °C. to 1100 °C.), has been found to have a simple rhombohedral structure, with a 0 = 5.057 /~ and c~ = 58.06 °, space group R3m, Z ----12. The atomic parameters have been obtained from a single crystal using the precession method. The structure may be described as composed of units of nearly regular icosahedra in a slightly deformed cubic close packing. This requires the use of three-center or delta bonds, wherein two electrons are shared by three boron atoms at the vertices of an equilateral triangle.

Diffraction Symmetry in Crystalline, Close-Packed C60

“…In this case the icosahedral molecule complies with crystallographic symmetry by retaining one three-fold axis and three mirror planes as in the case of boron icosahedra in β-B. [11,12] In R3m the layers follow (ABC...) stacking producing a pseudo-fcc unit cell. As in Fm3, twinning and disorder can produce apparent Fm3m symmetry by three-fold twinning operations along the body diagonals of a cube.…”

BH3 under Pressure: Leaving the Molecular Diborane Motif

“…The enthalpies of the elements are also shown in Figure 6 by a dashed line. Here the α-B 12 , γ-B 28 , and α-Ga phases 36 are used for B, and the P6 3 /m and C2/c phases 37 for H 2 , in their appropriate pressure ranges.…”

Electronic structures and mechanical properties of boron and boron-rich crystals (Part I)

“…It is believed that the most C-rich compound obtained so far is close to the composition B 12 C 3 but is slightly less than that, which is sometime referred to as awkward name B 4.3 C [43,44]. The simplest polymorph is α-rhombohedral boron, which was isolated in 1959 [45]. These three phases have rhombohedral lattices.…”