1. Jona F., Shirane G.: Ferroelectric Crystals. Pergamon Press, 1962.
2. Tisza L.: Phase Transformations in Solids. (Ed. by R. Smoluchowski, J. E. Mayer and W. A. Weyl.) John Wiley and Sons, Inc., New York 1951, p. 1.
3. Blinc R., Ribarič M.: Phys. Rev.130 (1963), 1816;
4. Villain J., Stamenkovič S.: Phys. stat. sol.15 (1966), 585;
5. Blinc R., Svetina S.: Phys. Rev.147 (1966), 430.