1. H. König and R. Hoppe, Z. Anorg. Allg. Chem. 439, 71 (1978).
2. S. F. Radaev, N. I. Sorokin, and V. I. Simonov, Fiz. Tverd. Tela (Leningrad) 33(12), 3597 (1991) [Sov. Phys. Solid State 33, 2024 (1991)].
3. I. N. Ogorodnikov, V. Yu. Yakovlev, A. V. Kruzhalov, and L. I. Isaenko, Fiz. Tverd. Tela (St. Petersburg) 44(6), 1039 (2002) [Phys. Solid State 44, 1085 (2002)].
4. I. N. Ogorodnikov, V. Yu. Yakovlev, B. V. Shul’gin, and M. K. Satybaldieva, Fiz. Tverd. Tela (St. Petersburg) 44(5), 845 (2002) [Phys. Solid State 44, 880 (2002)].
5. I. N. Ogorodnikov, E. A. Radzhabov, L. I. Isaenko, and A. V. Kruzhalov, Fiz. Tverd. Tela (St. Petersburg) 41(2), 223 (1999) [Phys. Solid State 41, 197 (1999)].