Novel ternary Y-B-C compound: Y_10+xB₇C_10-x (x 0.1)

A novel ternary Y-B-C compound Y_10+xB₇C _10-x is established. Y_10+xB₇C_10-x has a monoclinic crystal structure with space group C2/c (No.15) and lattice constants a 1.1273(14) nm, b 1.1159(14) nm, c 2.3566(30) nm and β 98.15(2)°. Y_10+xB₇C_10-x crystal rods were grown by floating zone technique and consisted of a predominant crystal phase and impurity phases. A small crystal having sufficient quality for single crystal XRD analysis could be selected. Structure refinement achieved a final R1 0.044 for 1660 independent reflections with F_o > 4s(F _o). 10 Y sites, 8 B sites, 9 C sites and one C/Y mixed occupancy site with about 0.9/0.1 occupation ratio were assigned. The unit chemical formula is Y_10+xB₇C_10-x (x0.1), and the unit cell contains 8 formula units. Y_10+xB₇C_10-x has a layer structure: Y-C double layers, in which Y and C bond alternatively like in the NaCl structure, spread parallel to the (001) plane and stack along the c-axis. The Y-C double layer is connected to the neighboring Y-C double layers via C-B-C chains or C-B-B-C chains. This structure was confirmed by electron diffraction and high-resolution electron microscopy. Magnetic susceptibility measurement indicated that the Y_10+xB₇C_10-x phase has no superconductivity above 2 K. A minor superconducting phase with T_c=7.5 K was observed, but ascribed to an unidentified impurity phase.