1. T. Watanabe, Res. Mechanica 11, 284 (1984)
2. E.G. Doni, G.L. Bleris, Phys. Stat. Sol. (a) 110, 393 (1988)
3. S. Lartigue, L. Priester, J. Am. Cer. Soc. 71(6), 430 (1988)
4. W. Bollmann, Mat. Sci. Eng. A 113, 129 (1989)
5. A.V. Shubnikov, N.V. Belov, Colored Symmetry, part II (Pergamon Press/MacMillan, New York, 1964)