1. Wu, M.K., Ashburn, J.R., Torng, C.J., Hor, P.H., Meng, R.L., Gao, L., Huang, Z.J., Wang, Y.Q., Chu, C.W.: Phys. Rev. Lett. 58, 908–910 (1987)
2. Housecroft, C.E., Sharpe, A.G., Housecroft, C.E.: Inorganic Chemistry (2005)
3. Greenwood, N.N., Earnshaw, A.: Chemistry of the Elements (Butterworth-Heinemann) (1997)
4. Jin, S., Tiefel, T.H., Sherwood, R.C., Davis, M.E.: Appl. Phys. Lett. 52, 2074 (1988)
5. Yang, W.M., et al: Physica C 307, 217 (1998)