On the crystal structure of boron carbides

Several crystals of boron carbide, grown from molten Cu, Pt, and Pd solutions using natural occurring as well as isotopically enriched boron, give essentially identical values for the lattice parameters. These parameters are consistent with carbon-saturated compositions near B4C. Detailed crystal structure refinement on some of these crystals yields positional and thermal parameters in good agreement with each other. More important, the thermal parameters of these studies are compared with those of crystals with lower carbon content (B13C2) as well as carbothermally prepared crystals. The thermal parameters of chain atoms for crystals with lower carbon content are both exceptionally large and much larger than those of crystals with composition near B4C. This result suggests that the crystals of lower carbon content contain a solid solution of C-B-C and C-B-B chains.