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Title: Superconductivity in Li-doped {alpha}-rhombohedral boron

Abstract

Metal transition and superconductivity were observed in Li-doped {alpha}-rhombohedral boron ({alpha}-B{sub 12}). The authors have established a purification method and obtained a large amount of high-purity {alpha}-B{sub 12} powder. Li doping into purified {alpha}-B{sub 12} was attempted by vapor diffusion processing (VDP) in a Mo or Ta tube. Li-doped {alpha}-B{sub 12} contained metallic glittering particles. Meissner effects were observed in such a compound with the nominal composition Li{sub x}B{sub 12} (x = 1.0, 1.4, 1.5, 1.7, or 2.5) (T{sub c} = 3.2-7 K). As for Li{sub 2.5}B{sub 12}, the temperature dependence of its electrical conductivity indicates a metallic character and its electrical resistivity drop is detected near the Meissner temperature. The existence of Li and Fermi edges in Li-doped {alpha}-B{sub 12} crystals was verified by transmission electron microscopy-electron energy loss spectroscopy (TEM-EELS). Lattice expansion, which is a well-known indicator of metal doping into a crystal, was also observed. Thus, Li doping into {alpha}-B{sub 12} was successfully achieved. Our work also suggests that it is possible to dope a larger amount of Li into {alpha}-B{sub 12} and to increase its T{sub c}.

Authors:
; ;  [1]; ;  [2]; ;  [3];  [4]
  1. Department of Advanced Materials Science, University of Tokyo (Japan)
  2. Department of Materials Science and Technology, Tokyo University of Science (Japan)
  3. Institute for Multidisciplinary Research for Advanced Materials, Tohoku University (Japan)
  4. Japan Atomic Energy Agency (Japan)
Publication Date:
OSTI Identifier:
21544763
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 83; Journal Issue: 18; Other Information: DOI: 10.1103/PhysRevB.83.184507; (c) 2011 American Institute of Physics
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; BORON; CRYSTALS; DIFFUSION; DOPED MATERIALS; ELECTRIC CONDUCTIVITY; ELECTRONS; ENERGY-LOSS SPECTROSCOPY; EXPANSION; LITHIUM ADDITIONS; METALS; PURIFICATION; SUPERCONDUCTIVITY; TEMPERATURE DEPENDENCE; TRANSMISSION ELECTRON MICROSCOPY; TRIGONAL LATTICES; ALLOYS; CRYSTAL LATTICES; CRYSTAL STRUCTURE; ELECTRICAL PROPERTIES; ELECTRON MICROSCOPY; ELECTRON SPECTROSCOPY; ELEMENTARY PARTICLES; ELEMENTS; FERMIONS; LEPTONS; LITHIUM ALLOYS; MATERIALS; MICROSCOPY; PHYSICAL PROPERTIES; SEMIMETALS; SPECTROSCOPY

Citation Formats

Nagatochi, T., Sumiyoshi, A., Kimura, K., Hyodo, H., Soga, K., Sato, Y., Terauchi, M., and Esaka, F. Superconductivity in Li-doped {alpha}-rhombohedral boron. United States: N. p., 2011. Web. doi:10.1103/PHYSREVB.83.184507.
Nagatochi, T., Sumiyoshi, A., Kimura, K., Hyodo, H., Soga, K., Sato, Y., Terauchi, M., & Esaka, F. Superconductivity in Li-doped {alpha}-rhombohedral boron. United States. doi:10.1103/PHYSREVB.83.184507.
Nagatochi, T., Sumiyoshi, A., Kimura, K., Hyodo, H., Soga, K., Sato, Y., Terauchi, M., and Esaka, F. 2011. "Superconductivity in Li-doped {alpha}-rhombohedral boron". United States. doi:10.1103/PHYSREVB.83.184507.
@article{osti_21544763,
title = {Superconductivity in Li-doped {alpha}-rhombohedral boron},
author = {Nagatochi, T. and Sumiyoshi, A. and Kimura, K. and Hyodo, H. and Soga, K. and Sato, Y. and Terauchi, M. and Esaka, F.},
abstractNote = {Metal transition and superconductivity were observed in Li-doped {alpha}-rhombohedral boron ({alpha}-B{sub 12}). The authors have established a purification method and obtained a large amount of high-purity {alpha}-B{sub 12} powder. Li doping into purified {alpha}-B{sub 12} was attempted by vapor diffusion processing (VDP) in a Mo or Ta tube. Li-doped {alpha}-B{sub 12} contained metallic glittering particles. Meissner effects were observed in such a compound with the nominal composition Li{sub x}B{sub 12} (x = 1.0, 1.4, 1.5, 1.7, or 2.5) (T{sub c} = 3.2-7 K). As for Li{sub 2.5}B{sub 12}, the temperature dependence of its electrical conductivity indicates a metallic character and its electrical resistivity drop is detected near the Meissner temperature. The existence of Li and Fermi edges in Li-doped {alpha}-B{sub 12} crystals was verified by transmission electron microscopy-electron energy loss spectroscopy (TEM-EELS). Lattice expansion, which is a well-known indicator of metal doping into a crystal, was also observed. Thus, Li doping into {alpha}-B{sub 12} was successfully achieved. Our work also suggests that it is possible to dope a larger amount of Li into {alpha}-B{sub 12} and to increase its T{sub c}.},
doi = {10.1103/PHYSREVB.83.184507},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 18,
volume = 83,
place = {United States},
year = 2011,
month = 5
}
  • Iron and/or aluminum are doped to {beta}-rhombohedral boron, and the electrical conductivity and {sup 57}Fe Moessbauer effect are measured. The temperature dependence of the electrical conductivity is explained as a variable range hopping type. The conductivity increases with an increase in Fe concentration, but it is insensitive to Al concentration. The Moessbauer spectra measured at room temperature are resolved into three kinds of doublets and a sextet due to ferromagnetic FeB. One doublet, {gamma}{sub 0}, is attributed to Fe{sup 3+} ions at A{sub 1} sites, while the others, {gamma}{sub 1} and {gamma}{sub 2}, occur from Fe{sup 2+} ions at Dmore » sites. When Fe and Al atoms are simultaneously doped into {beta}-boron, the intensity of the {gamma}{sub 0} doublet decreases and, hence, those of the {gamma}{sub 1} and {gamma}{sub 2} doublets relatively increase. The results shows that Fe atoms are moved from A{sub 1} corresponds to Fe{sup 2+} (D)-Fe{sup 2+}(D) and the {gamma}{sub 2} doublet to Fe{sup 2+}(D) and that a part of Fe{sup 2+}(D) is in the magnetic state at 4.2 K.« less
  • To get information on the electronic states in the band gap of beta-rhombohedral boron, optical and photoelectric properties of samples with C contents up to 3250 ppm were investigated. The low-temperature phase transition is shown to be independent of the C content. Carbon acts as donor and evokes occupied electronic ground states in the energy range of the hole trapping level near the valence band edge, and excited states in the band gap. Simultaneous measurements of optical absorption and electrical conductivity yield valuable information on the transport process, and indicate diffusion processes of trapped carriers even at low temperatures.
  • High-T{sub C} superconductivity is possible upon metallic-element doping into {beta}-rhombohedral boron ({beta}-B{sub 105}), which is one of the boron icosahedral cluster solids. We attempted magnesium (Mg) doping into {beta}-B{sub 105} and discussed the possibility of metal transition and superconductivity. We achieved Mg doping into {beta}-B{sub 105} at a high Mg concentration of up to MgB{sub 11.5} (8.6 Mg/cell), i.e., electron doping sufficient for the Fermi energy (E{sub F}) to reach the conduction band over the intrinsic acceptor level (IAL) and trapping levels. However, neither metal transition nor superconductivity was observed. The changes in the structure and electronic properties are discussedmore » on the basis of the results of x-ray powder diffraction using the Rietveld method and electrical conductivity and magnetic susceptibility measurements, respectively. We estimated the density of states near E{sub F} and discussed the electronic states of {beta}-B{sub 105}. From the result, it is suggested that a localized state exists above the IAL probably originating from the B{sub 28} cluster with structural defects.« less
  • A crystal structure of aluminum doped {beta}-rhombohedral boron was studied by single-crystal X-ray diffraction at 80 K. The crystals were synthesized using high-pressure high temperature technique at 3 GPa and 2100 K. The structure is based on three-dimensional framework made of B{sub 12} icosahedra with voids occupied by the B{sub 28}-B-B{sub 28} units, it has the R-3m space group with a=10.9014(3), c=23.7225(7) A lattice dimensions in hexagonal setting. Aluminum atoms are located in A1 and D special positions of the {beta}-B structure with occupancies of 82.7(6)% and 11.3(4)%, respectively. Additional boron atoms are located near the D-site. Their possible distributionmore » is discussed. Finally we have found two appropriate structural models whose refinement suggests two possible chemical compositions, AlB{sub 44.8(5)} and AlB{sub 37.8(5)}, which are in a good agreement with the chemical analysis data obtained from EDX. The crystal structure of AlB{sub 44.8(5)} is described in detail. - Graphical abstract: The atomic distribution near the B(15) atom (non-labeled atom in the center of the picture) shown along the c axis. Anisotropic displacement ellipses for Al(2) (D-site) and B(15) are shown with 50 % probability level. The mirror plane with Miller indices (1 1 0) and related to it (-1 2 0) and (-2 1 0) generated by the 3-fold rotation-inversion axis parallel to the c axis splits the position of B(16) over two sites. Highlights: Black-Right-Pointing-Pointer The crystal structure of the AlB{sub 44.8(5)} has been refined. Black-Right-Pointing-Pointer Aluminum atoms partially fill certain types of voids (the A1- and D-sites). Black-Right-Pointing-Pointer We have got two possible models of atomic distribution near the D-site.« less
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