2005 Fiscal Year Final Research Report Summary
Search for High Critical Temperature Superconductivity in Li- or Mg-doped Boron Icosahedral Cluster Solids
| Project/Area Number |
15360332
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Physical properties of metals
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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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| Co-Investigator(Kenkyū-buntansha) |
SOGA Kohei The University of Science, Department of Materials Science and Technology, Lecturer, 基礎工学部, 講師 (50272399)
KAWAGUCHI Kenji Nanoarchitectonics Research Center, National Institute of Advanced Industrial Science and Technology, Senior Researcher, 界面ナノアーキテクトニクス研究センター, 主任研究員 (80344141)
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| Project Period (FY) |
2003 – 2005
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| Keywords | superconductor / boron-rich semiconductor / icosahedral cluster / high symmetry / doping / variable-range hopping conduction / Pauli naramagnetic / structurally complex material |
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| Research Abstract |
There is a possibility of high-Tc superconductivity upon metallic-element doping into β-rhombohedral boron (β-B^<105>), which is one of the boron icosahedral cluster solids. We attempted magnesium (Mg) doping into β-B^<105> and discussed the possibility of metal and superconductive transitions. We achieved a higher concentration of Mg doping into β-B^<105>, up to MgB_<11.5> (8.6 Mg/cell), i.e., electron doping sufficient for the Fermi energy (E_F) to reach over the intrinsic accepter level (IAL). However, neither metal nor superconductive transition was observed. The change in the structure and electronic properties are discussed on the basis of the X-ray powder diffraction (XRD), using the Rietveld method, and electrical conductivity and magnetic susceptibility measurements, respectively. We estimated the density of states (DOS) at the E_F and discussed the electronic states of β-B^<105>. As a result, it is suggested that a localized state exists above the IAL probably originating from B28 cluster with structural defects.
We measured electrical conductance of single crystalline boron nanobelts having α-tetragonal crystalline structure. The doping experiment of Mg was carried out by vapor diffusion method. The pure boron nanobelt is a p-type semiconductor and its electrical conductivity was estimated to be on the order of 10^<-3> (Ωcm)^<-1> at room temperature. The carrier mobility of pure boron nanobelt was measured to be on the order of 10^<-3> (cm^2/Vs) at room temperature and has an activation energy of 〜0.19 eV. The Mg-doped boron nanobelts have the same α-tetragonal crystalline structure as the pristine nanobelts. After Mg vapor diffusion, the nanobelts were still semiconductor, while the electrical conductance increased by a factor of 100〜500. Transition to metal or superconductor by doping was not observed.
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Research Products
(16 results)
