4) S.Sudo, M.Kawachi, T.Edahiro and N.Inagaki: Electrical Communication Laboratory technical journal/the Electrical Communication Laboratory, Nippon Telegaraph and Telephone Public Corporation, 29(1980)1719-1729.
5) W.D. Kingery, H.K. Bowen and D.R. Uhlmann : Introduction to Ceramics Second Edition, (UCHIDA ROKAKUHO, Tokyo, 1980), pp.250-255.