1. Shuvalov, L.A., Kristallogr., 1963, vol. 8, p. 616.
2. Aizu, K., Phys. Rev. B, 1970, vol. 2, p. 754.
3. Shabel’nikov, L.G., Shekhtman, V.Sh., and Tsarev, O.M., Fiz. Tverd. Tela, 1976, vol. 18, p. 1529.
4. Afonnikova, N.S., Shmyt’ko, I.M., and Shekhtman, V.Sh., Izv. Akad. Nauk SSSR, Ser. Fiz., 1979, vol. 43, no. 8, p. 1611.
5. David, W.I.F. and Wood, I.G., J. Phys. C: Solid State Phys., 1983, vol. 16, p. 5149.