Remarks on the Modified Potassium Dihydrogen Phosphate Model of a Ferroelectric

The modified potassium dihydrogen phosphate (KDP) model of a two-dimensional ferroelectric with the inclusion of an arbitrary electric field E is considered. The nature of the phase transition is unaffected by the inclusion of an external field, whereas the transition temperature depends on E with Tc→∞ as E→∞, and Tc→0 as E→somespecialvalues. We also find that Tc is determined by different relations in different regions in the E plane, a property not shared by the Slater KDP model. Among the other thermodynamic properties discussed, the critical behavior of the polarizability is shown to be χ~(T-Tc)^-1/2. It is shown that this model is identical to the problem of close-packed dimers on a hexagonal lattice.