Models of the phase transition in kdp type ferroelectrics

Abstract

Recent typical models proposed for KDP type ferroelectrics, the Ising spin models, the tunneling proton model, and the 'mixed' proton and phonon model (the modified tunneling model), are briefly reviewed and compared with experimental facts. The relations between these models are correctly shown paying attention to the expressions for the electric polarization in them. Experimental and theoretical work necessary for deciding upon a definite final model are suggested.