A novel boroncarbide, Y 2B 3C 2: X-ray single crystal and neutron powder diffraction analysis

Abstract

The crystal structure of Y 2B 3C 2 was analysed by means of room temperature X-ray single crystal and neutron powder diffractometry. Y 2B 3C 2 crystallises with the Gd 2B 3C 2-type (space group: Cmmm - No. 65, Z=2). The unit cell dimensions are: a=0.3405(5), b=1.3765(6), c =0.3631(6) nm, b/a=4.044, V=0.1702 nm 3 the X-ray density is: ρ x=4.57 Mgm −3. The structure was solved by combined Patterson-Difference Fourier methods. Residual values are: R F=Σ ΔF /Σ F o =0.027, R w=0.020, for an asymmetric set of 232 independent reflections ( F o >3 σ( F o )). Boron atoms B1, each in triangular metal co-ordination, form infinite zigzag chains ( d B1–B1=0.1923 nm) branched with carbon atoms. Bond angles in the chain are ϕ B1–B1–B1=124.6°. Carbon atoms are at a distance of d B1–C=0.1552 in rectangular co-ordination of four metal atoms. The branched boron chains are connected by a bridging boron atom B2 linking the carbon atoms in form of a linear bridge at d C–B2=0.1442 nm. Rietveld refinement of the neutron powder data from Y 2B 3C 2( 11B–isotope) confirms the nuclear structure arrangement as well as the full occupancy of all the non-metal atom sites.