1. J.G. Bednorz and K.A. Muller, Z. Phys. B 64, 189 (1986).
2. M.K. Wu, J.R. Ashburn, C.J. Torng, P.H. Hor, R.L. Meng, L. Gao, Z.J. Huang, Y.Q. Wang, and C.W. Chu, Phys. Rev. Lett. 58, 908 (1987).
3. Y. Bando, T. Terashima, K. Iijima, K. Yamamoto, K. Hirata, K. Hayashi, K. Kamigaki, and H. Terauchi, Proc. XII Intl. Cong, for Electron Microsc. (1990)
4. J.Q. Zheng, X.K. Wang, M.C. Shih, S.J. Lee, S. Williams, J. So, P. Dutta, J.B. Ketterson, and R.P.H. Chang, Proc. 2nd. Intl. Conf. on Electronic Mater. 85(1990)
5. M.G. Norton and C.B. Carter, J. Cryst. Growth 110, 645 (1991)