A Novel Boron-rich Scandium Borocarbosilicide; Sc0.83-xB10.0-yC0.17+ySi0.083-z (x=0.030, y=0.36 and z=0.026): Floating Zone Crystal Growth and Structure Analysis

Single crystals of a novel boron-rich scandium borocarbosilicide Sc0.83-xB10.0-yC0.17+ySi0.083-z were grown by the floating zone method using a four-xenon lamp mirror-type image furnace. Structure analysis using single-crystal X-ray diffraction data showed that Sc0.83-xB10.0-yC0.17+ySi0.083-z has a face-centered cubic with lattice constant a=2.03085 nm and space group of F 3m. The crystal composition calculated from the structure analysis was ScB12.0C0.65Si0.071 which agreed with the measured composition of ScB12.7C0.62Si0.08. In the crystal structure which is a new structure type of boron-rich borides, there are three structurally independent B12 icosahedra I(1), I(2) and I(3) and one B10 polyhedron which interconnect each other to form a three-dimensional boron framework. There are four fully occupied bridging sites, one is the C site and the other three sites are occupied statistically by B or C. The Sc atoms reside in three interstitial sites of the boron framework. Two Si sites are tetrahedrally surrounded by the bridging carbon sites and by the bridging boron/carbon mixed occupation sites, respectively. The boron framework structure can be understood more easily by introducing larger structure units, they are a super tetrahedra T(1) made up by four icosahedra I(1), a super tetrahedra T(2) made up by four icosahedra I(2) and a super octahedra O(1) made up by six icosahedra I(3).