New quaternary carbon and nitrogen stabilized polyborides: REB15.5CN (RE: Sc, Y, Ho, Er, Tm, Lu), crystal structure and compound formation

A new family of quaternary carbon and nitrogen containing Rare Earth (RE: Sc, Y, Ho, Er, Tm and Lu) borides: REB 15.5 CN, has been synthesized and structurally characterized by powder X-ray diffraction data. They are all isotypic with Sc 1-x B 15.5 CN whose structure was solved based on single-crystal X-ray data and HRTEM investigations. The structure refinement converged at a R(F 2 ) value of 0.044 for 364 reflections. The new structure type of Sc 1-x B 15.5 CN is composed of a three-dimensional network based on interconnected slabs of boron (B 12 ) ico icosahedra and (B 6 ) oct octahedra. A linear [CBC] chain and nitrogen tightly bridges icosahedra. Sc partially occupies voids in the sheets of boron octahedra. It crystallizes with the trigonal space group P 3 m1, with Z = 2. Lattice parameters (nm) are as follows: for RE: Sc, a,b = 0.5568(4), c = 1.0756(2): Y, a,b = 0.55919(6), c = 1.0873(2); Ho, a,b = 0.55883(7), c = 1.0878(6); Er, a,b = 0.55889(5), c = 1.0880(6); Tm, a,b = 0.5580(1), c = 1.0850(6); Lu, a,b = 0.55771(9), c = 1.0839(4). Magnetic characterization of ErB 17 C 1.3 N 0.6 has been performed.