1. Incommensurate Phases in Dielectrics, Ed. by R. Blinc and A. P. Levanyuk (North-Holland, Amsterdam, 1986), Vols. 14.1 and 14.2.
2. H. Z. Cummins, Phys. Rep. 185(5–6), 211 (1990).
3. D. G. Sannikov and A. P. Levanyuk, Fiz. Tverd. Tela (Leningrad) 20(4), 948 (1978) [Sov. Phys. Solid State 20, 580 (1978)].
4. D. G. Sannikov and V. A. Golovko, Fiz. Tverd. Tela (Leningrad) 26(4), 1117 (1984) [Sov. Phys. Solid State 26, 678 (1984)].
5. J. M. Yeomans, in Solid State Physics (Academic, Orlando, 1988), Vol. 41.