1. a Ube Industries Co., Ltd., Kogushi, Ube, Yamaguchi 755, Japan
2. b Department of Materials Physics and Chemistry, Graduate School of Engineering, Kyushu University, Higashi-ku, Fukuoka 812-8581, Japan
3. c Department of Materials Physics and Chemistry, Graduate School of Engineering, Kyushu University, Higashi-ku, Fukuoka 812-8581, Japan