Synthesis and Properties of [B/C] Layered Compounds
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Synthesis and Properties of [B/C] Layered Compounds. Takao Mori1,2 1 National Institute for Materials Science, Namiki 1-1, Tsukuba, Japan 305-0044 2 PRESTO, Japan Science and Technology Agency, Honcho 8-4-1, Kawaguchi, Japan ABSTRACT We report synthesis and properties of layered compounds with 2D boron-and-carbon-mixed-atomic-layers which are related to topics of recent high interest. The previous discovery of the first [B/C] graphite intercalation-like compound Sc2B1.1C3.2 and evaluation of reported high temperature ferromagnetism in CaB2C2 are reviewed. MgB2 related [B/C] compounds MgB2C2 and LiBC were synthesized and hole doping carried out in search for superconducting materials with high TC. Superconductivity was not observed for any of the compounds above 1.8 K, but (Mg,Li)B2C2 is demonstrated to be the most promising system, with an insulator to metal transition indicated to be induced. INTRODUCTION Network compounds, namely, cluster-based or 2D atomic net-containing compounds are a class of materials which has been attracting increasing interest. The carbon systems are well known such as the cluster C60 fullerene compounds and the 2D graphite intercalation compounds (GIC’s). Boron-containing compounds are also known to form cluster compounds or compounds with 2D atomic nets. However, the main focus up to now for the boron network compounds has been on the interesting structural properties or mechanical properties. We have been trying to develop new functional materials in the boron network compounds. Regarding the boron cluster compounds we have synthesized novel B12 icosahedra-containing compounds which display magnetism. A wide range of magnetic behavior has been found in these insulating dilute f-electron systems ranging from 3D long range order, 2D spin glasses, and 1D-like magnetism [1-4]. On the other hand, considering 2D atomic net-containing compounds, metal borocarbides containing boron and carbon mixed 2D [B/C] layers have been known to be interesting materials. Structurally, a wide variation in the coordination of the [B/C] layer is exhibited depending on the type/size of metal atoms sandwiched in between, even for compounds with the same stoichiometry [5,6]. We have previously discovered the first [B/C] graphite intercalation-like compound, Sc2B1.1C3.2 which has a [B1C2]∞ graphitic layer [7]. The properties of this [B/C] GIC and evaluation of the reported high temperature ferromagnetism will be reviewed. We also present new developments in hole-doping MgB2 related compounds EXPERIMENTAL Synthesis of Sc2B1.1C3.2 was carried out by first preparing Sc2C1-x by the carbothermal reduction of scandium oxide under vacuum. The required amount of boron and carbon were added and the mixture reacted again. Heating was performed in BN crucibles surrounded by inductively heated graphite susceptors. In the case of Sc2B1.1C3.2, crystals were grown by the floating zone (FZ) method in a xenon lamp image furnace. Synthesis of CaB2C2, LiBC, and MgB2C2 were carried out by crushing and well mixing the necessa
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