Floating Zone Crystal Growth and Structure Analysis of a Novel ScB19 Family Compound, ScB19+xSiy

Single crystals of a novel ScB19 family compound ScB19+xSiy were grown by the floating zone method using a four-lamp mirrortype image furnace. A small amount of silicon addition to ScB19 which decomposes at elevated temperatures without melting allowed it to coexist with the liquid phase and as a resultant made the floating zone crystal growth possible. Powder X-ray diffraction analysis confirmed the grown crystals of ScB19+xSiy to be isostructural to ScB19. It was found that the crystal structure of ScB19+xSiy solved based on single-crystal X-ray data is tetragonal with lattice constants of a, b=1.03081(2) nm, c= 1.42589(3) nm, space group P41212 or P43212 and is basically isotypic with ALPHA-AlB12 structure type. In the crystal structure boron atoms form a three-dimensional framework based on interconnected B12 icosahedra and B22 polyhedra. The Sc atoms reside in three of five Al sites in the ALPHA-AlB12 structure and Si resides in a bridge site bonding two B22 units.