1. A. Iandelli and A. Palenzona, Handbook of the Physics and Chemistry of Rare Earths, K. A. Gschneidner Jr. and E. Eyring Eds., North-Holland, Amsterdam, 1979, vol. 2, p. 1.
2. M. M. Carnasciali, G. A. Costa and E. A. Franceschi, Gazz. Chim. Ital., 113 (1983) 239.
3. G. A. Costa, E. A. Franceschi and A. Tawansi, J. Less-Common Met., in press.
4. M. M. Carnasciali, G. A. Costa and E. A. Franceschi, J. Less-Common Met., 92 (1983) 97.
5. P. Morin and J. Laforest, Comptes Rendus Acad. Sci., B277 (1973) 353.