1. Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan, Hiroshima City Industrial Promotion Center, Senda-machi 3-8-24, Hiroshima 730-0052, Japan, Present address: Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore-560 064, India