SPring-8, the large synchrotron radiation facility

Release Date

11 Apr, 2007

 Prof. H. Hosono (Tokyo Institute of Technology) and coworkers have succeeded in realizing metallic state in representative insulating material 12CaO•7Al₂O₃, which is a constituent of alumina cement, by doping carrier electron to >1x10²¹ cm^-3.  A clear metal-insulator transition was observed at the critical concentration of 1x10²¹ cm^-3.  This is a first metallic state realized in light-metal oxides which are most abundant on earth but are widely believed to be insulators. Appearance of the presence of resistivity minimum at a low temperature, Kondo effect, was distinctly observed upon doping magnetic impurities, substantiating the realization of metallic state in the samples. The maximum conductivity at RT is 1,500 Scm^-1, which is close to that in graphite.
 Analysis of powder X-ray diffraction data, acquired at the Powder Diffraction Beamline BL02B2 of SPring-8, revealed that the mechanism for this metal-insulator transition is strikingly different from that reported so far. The results provide an approach for the realization of electroactive functions in materials composed only of environmentally benign elements by utilizing the appropriate nanostructures.

Publication:
"Metallic State in a Lime-Alumina Compound with Nanoporous Structure"
Sung Wng Kim, Satoru Matsuishi, Takatoshi Nomura, Yoshiki Kubota, Masaki Takata, Katsuro Hayashi, Toshio Kamiya, Masahiro Hirano, and Hideo Hosono
Nano Lett., 7 (5), 1138 -1143, (2007), Web Release Date: March 22, 2007