1. W. Eitel and W. Skaliks,Z. Anorg. Allg. Chem.,183, 263 (1929).
2. L. S. Itkina and N. M. Chapligina,Zh. Neorg. Khim.,8, 1479 (1963).
3. M. Christmann, N. Sadeghi, and G. Papin,Rev. Chim. Minerale,15, 312 (1978).
4. V. A. D'yakov, C. A. Ebbers, M. V. Pchelkin, and V. I. Pryalkin, in:Technical Digest of the 15th Intern. Conference on Coherent and Nonlinear Optics, St. Petersburg (1995), Vol. 2, p. 219.
5. A. V. Yatsenko, S. G. Zhukov, V. A. D'yakov, et al.Mater. Res. Bull.,30, 739 (1995).