1. Research and Development Center, Japan Insulation Co., Ltd., Hozumi, Gifu, 501-0232, Japan, Ceramic Research Institute, National Institute of Advanced Industrial Science and Technology, Hirate-cho, Kita-ku, Nagoya 462-8510, Japan, and Department of Earth and Planetary Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima, 739-8526, Japan