2001 Fiscal Year Final Research Report Summary
Production of Nanotubes by Thermal Annealing and Development of Boron-Network Solids
| Project/Area Number |
11165209
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| Research Category |
Grant-in-Aid for Scientific Research on Priority Areas (A)
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| Allocation Type | Single-year Grants |
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| Research Institution | The University of Tokyo |
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Principal Investigator |
KIMURA Kaoru The University of Tokyo, Graduate School of Frontier Sciences, Professor, 大学院・新領域創成科学研究科, 教授 (30169924)
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| Project Period (FY) |
1999 – 2000
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| Keywords | Amorphous Boron / α-rhombohedral Boron / β-rhombohedral Boron / BN Nanotube / BN Nanocone / Metal-Insulator Transition / Superconductivity / Metallic-Covalent Bonding Conversion |
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| Research Abstract |
1) Formation conditions of BN nanotubes by thermal annealing under Li vapor starting from a mixed powder of amorphous boron (a-B) and hexagonal boron nitride (h-BN) were investigated. BN nanotubes and the surrounding structures of twisted BN layers could be produced using h-A1N instead of h-BN as the starting material. However, they were not formed by nitridation of a-B in N_2 gas and by thermal annealing of h-BN under Li vapor. Therefore they are considered to form by nitridation of a-B under Li vapor. When β-rhombohedral boron (β-B) was used as the starting material instead of a-B, two new structures were discovered. They were zigzag-type nanotubes growing from edge of h-BN particles along one of <10-10> directions of the particles and piles of monolayer BN cones with apex angle of about 20°.
2) Metal transition and superconductivity were searched in Li-doped α-rhombohedral boron (α-B). As a result of Reitvelt analysis for the Li-doped α-B, the changes of lattice constants were below 0.1 % and Li was doped not in the whole of specimen. Parts of the sample had metallic luster and metal transition was suggested by the appearance of Fermi edge and chemical shift after Li doping. In magnetic susceptibility of the sample measured by SQUID magnetometer, a superconductive component was considered to superpose on a ferromagnetic one. However, volume fraction of the superconductive phase was about 0.02 %.
3) Metal transition occurred in a-B by about 1 at.% Vanadium (V) doping, though the icosahedral cluster(B_<12>)-based local structure was maintained until several at.%. By V occupation of the site in a-B similar to the A_1-site in β-B, the bonding nature of surrounding four B_<12> was considered to convert from covalent to metallic. This contrast that metallic bonding conversion and then metallic transition occur by more than 10 at.% metal doping in a-Si with destruction of the tetrahedral configuration and construction of metallic compound-like structure.
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