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

Single crystals of a novel ScB₁₉ family compound ScB_19+xSi_y were grown by the floating zone method using a four-lamp mirror-type 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 ScB_19+xSi_y to be isostructural to ScB₁₉. It was found that the crystal structure of ScB_19+xSi_y 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 α-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 α-AlB₁₂ structure and Si resides in a bridge site bonding two B₂₂ units.