Abstract
Boron carbide phases exist over a widely varying compositional range B12+xC3-x (0.06 < x < 1.7). One idealized structure corresponds to the B13C2 composition (space group R-3m) and contains one icosahedral B12 unit and one linear C—B—C chain. The B12 units are composed of crystallographically distinct B atoms BP (polar, B1) and BEq (equatorial, B2). Boron icosahedra are interconnected by C atoms via their BEq atoms, forming layers parallel to (001), while the B12 units of the adjacent layers are linked through intericosahedral BP—BP bonds. The unique B atom (BC) connects the two C atoms of adjacent layers, forming a C—B—C chain along [001]. Depending on the carbon concentration, the carbon and BP sites exhibit mixed B/C occupancies to varying degrees; besides, the BC site shows partial occupancy. The decrease in carbon content was reported to be realized via an increasing number of chainless unit cells. On the basis of X-ray single-crystal refinement, we have concluded that the unit cell of the given boron-rich crystal contains following structural units: [B12] and [B11C] icosahedra (about 96 and 4%, respectively) and C—B—C chains (87%). Besides, there is a fraction of unit cells (13%) with the B atom located against the triangular face of a neighboring icosahedron formed by BEq (B2) thus rendering the formula B0.87(B0.98C0.02)12(B0.13C0.87)2 for the current boron carbide crystal.
Highlights
Boron carbide phases exist over a widely varying compositional range B12+xC3-x (0.06 < x < 1.7)
One idealized structure corresponds to the B13C2 composition and contains one icosahedral B12 unit and one linear C—B—C
The B12 units are composed of crystallographically distinct B atoms BP and BEq
Summary
One idealized structure corresponds to the B13C2 composition (space group R3m) and contains one icosahedral B12 unit and one linear C—B—C chain. Boron icosahedra are interconnected by C atoms via their BEq atoms, forming layers parallel to (001), while the B12 units of the adjacent layers are linked through intericosahedral BP—. The unique B atom (BC) connects the two C atoms of adjacent layers, forming a C—B—C chain along [001]. On the basis of X-ray singlecrystal refinement, we have concluded that the unit cell of the given boron-rich crystal contains following structural units:. There is a fraction of unit cells (13%) with the B atom located against the triangular face of a neighboring icosahedron formed by BEq (B2) rendering the formula B0.87(B0.98C0.02)12(B0.13C0.87) for the current boron carbide crystal
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have