On the Theory of Ferroelectric Susceptibilities

Recently M. Tokunaga has published two interesting papers (J. Phys. Soc. Jpn. 56 (1987) 1653; 57 (1988) 4275) that relate the fluctuating polarizations p c in the paraelectric phases of ferroelectrics (estimated from the Curie constants determining the dielectric susceptibilities) and the spontaneous polarizations P S at low temperatures. The ratios of these polarizations were discussed in terms of self-consistent phonon theory. In the present paper these results are related to earlier studies by Jaynes and Wigner, by Mason and Matthias, and others.