1. B. E. Kogan, E. P. Skripa, Trace Elements, Rew., Material and Economy, Moscow, 9 (1973) 8.
2. X. Gungxian, X. Gimei, New Frontiers of Rare Earth Science and Applications, Vol. 2, Beijing, Science Press, 1985, p. 1505.
3. G. Bosheng, Inorg. Chem. Acta, 140 (1987) 353.
4. G. Bosheng, X. Bingkun, Rare Earths in Agriculture, National Agriculture Science Press, Beijing, 1992, p. 1012.
5. D. K. Teherant, J. Radioanal. Nucl. Chem., 117 (1987) 133.