2006

BoronI 0055 Calcium Tetraboride—Does It Exist? Synthesis and Properties of a Carbon-

-Doped Calcium Tetraboride that Is Isotypic with the Known Rare Earth Tetra-borides. — Single crystals of carbon-doped CaB4 are prepared by solid state reaction of the elements (sealed Nb tube, 1000 °C, 60 h). The presence of carbon is found to be essential in the synthesis of the tetraboride. CaB4 crystallizes in the tetragonal space group P4/mbm with Z = 4. The structure consists of a three-dimensional boron network built up by B6 octahedra and B2 dumbbells, as observed in the structures of rare earth tetraborides. Band structure calculations indicate that CaB4 is a stable semiconducting compound with a narrow band gap and that carbon should not necessarily be required for the stability of this compound. The distribution of boron and carbon atoms in the structure is investigated by 11B and 13C MAS NMR. Measurements of the magnetic susceptibility indicate a temperature-independent paramagnetism down to 20 K. — (SCHMITT, R.; BLASCHKOWSKI, B.; EICHELE, K.; MEYER*, H.-J.; Inorg. Chem. 45 (2006) 7, 3067-3073; Inst. Anorg. Chem., Eberhard-Karls-Univ., D-72076 Tuebingen, Germany; Eng.) — Schramke

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