Rare earth metal borocarbides

Structural, Electronic, and Magnetic Properties of Ternary Rare-Earth Metal Borocarbides R5B2C5 (R=Y, Ce–Tm) Containing BC2 “Molecules”

“…Preliminary results on the structure re"nements of Sm B C and Gd B C indicate that they crystallize in the tetragonal space P4/ncc}D F (No. 130) group with the lattice parameters a"8.331 (1) structures show a strong tendency for twinning with a mechanism similar to that recently observed for Sc C (5). These structures have NaCl-related layers (those with the Sm C octahedra) which are bridged via the BC units.…”

“…These chains are nearly linear with B}C distances of 1.47(2) and 1.46(1) A s in Sm B C and Gd B C , respectively, suggesting double bond character. Indeed, each carbon atom of the BC groups is accomodated in an [R B] octahedron, a common feature in the ternary rareearth metal boron carbide compounds (1). The presence of only one carbon atom in the nearly regular rare-earth metal octahedra in R B C instead of a C dumbbell as observed in R B C is probably due to the smaller size of the rareearth metal in play (it is noteworthy to mention that both stoichiometries R B C (with isolated C atoms) and R B C (with C units) exist only for Ce).…”

“…Nevertheless, we should point out that elongated rare-earth metal octahedra with C pairs occur in the whole series of binary RC carbides. R}R, R}B (1), R}C (1), and R-C(2) bonding contacts (which are in the range of 3.48}3.83, 2.68}2.82, 2.50}2.74 and 2.53}2.81 A s for Sm B C for instance) are comparable to those commonly measured in this kind of compound (1). A detailed description of the Sm B C structure together with the related structures of Ce B C (14) and binary Sc C (5) will be published in a forthcoming paper devoted to the twinning in these structures (15).…”

“…In these compounds, boron and carbon atoms generally form either twodimensional (2D) networks, which alternate with 2D sheets of metal atoms, or one-dimensional (1D) carbon-branched zigzag boron chains running into channels built by the metal atoms, or "nite pseudomolecules of various sizes trapped into holes built by the metallic matrix. Such a broad diversity of original topologies, especially with respect to the bonding within the nonmetal frameworks, have rendered these compounds of interest for the theoretical chemists, who have rather quite intensively studied their electronic properties (1). In contrast, little is known about the magnetic behavior of these compounds (2}4).…”

Interaction of lanthanum with boron and carbon: phase diagram and structural chemistry

“…The structures of the ternary rare earth (RE) boride carbides display a variety of 5 different arrangements with boron carbon substructures. They extend from zero-dimensional 6 units to chains and two-dimensional nets embedded in the metal atom sublattices as well as 7 interconnected boron icosahedra [1,2]. The substructures can be divided into three groups.…”