1. M. O’Keeffe, Science 180, 1276 (1973).
2. A. I. Livshits, V. M. Buznik, P. P. Fedorov, and B. P. Sobolev, Nuclear Magnetic Resonance in Crystals (Inst. Fiziki Sib. Otd. Akad. Nauk SSSR, Krasnoyarsk, 1978), p. 90.
3. V. Trnovcova, P. P. Fedorov, B. P. Sobolev, et al., Kristallografiya 41(4), 731 (1996) [Crystallogr. Rep. 41, 694 (1996)].
4. V. Trnovcova, P. P. Fedorov, M. D. Valkovskii, et al., Ionics 3, 313 (1997).
5. N. I. Sorokin and M. W. Breiter, Solid State Ionics 99, 241 (1997).