1. M E Lines and A M Glass, Principles and applications of ferroelectrics and related materials (Clarendon Press, Oxford, 1977)
2. J Stankowski, Phys. Rep. 77, 1 (1981)
3. F H Allen, Acta Crystallogr. B58, 380 (2002)
4. M I Kay and R Kleinberg, Ferroelectrics 5, 45 (1973)
5. G M Sheldrick, SHELXLS97 and SHELXL97 (University of Gottingen, Germany, 1997)