1. J.G. Bednorz, K.A. Müller. Z. Physik B64, 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, C.W. Chu: Phys. Rev. Lett.58, 908 (1987)
3. See, for example, M.B. Maple, Y. Dalichaouch, J.M. Ferreira, R.R. Hake, B.W. Lee, J.J. Neumeier, M.S. Torikachvili, K.N. Yang, H. Zhou, R.P. Guertin, M.V. Kuric: Physica148B, 155 (1987) and references therein
4. R.J. Cava, B. Batlogg, R.B. van Dover, D.W. Murphy, S. Sunshine, T. Sigrist, J.P. Remeika, E.A. Rietman, S. Zahurak, G.P. Espinosa: Phys. Rev. Lett.58, 1676 (1987)
5. F.S. Galasso:Structure, Properties and Preparation of Perovskite-Type Compounds (Pergamon, New York 1969) Chap.2