1. Ganglberger, E.: Z. Kristallogr. 128 (1969) 438.
2. Dewally, D., Perrot, P., Leroy, J.M., Tridot, G.: C. R. Acad. Sci. (Paris) Ser. C270 (1970) 1980 (in French).
3. Noël, H., Padiou, J., Prigent, J.: C. R. Acad. Sci. (Paris) Ser. C 272 (1971) 206 (in French).
4. Noël, H.: C. R. Acad. Sci. (Paris) Ser. C 277 (1973) 463 (in French).
5. Noël, H.: C. R. Acad. Sci. (Paris) Ser. C 279 (1974) 513 (in French).