1. National Institute for Research in Inorganic Materials, 1-1 Namiki, Tsukuba, Ibaraki 305-0044
2. Department of Physical Science, Faculty of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526
3. Institute of Materials Science, University of Tsukuba, Tennodai, Tsukuba, Ibaraki 305-8573