Hydrogen-bond configuration parameters for ferroelectrics isomorphic to KH(2)PO(4)

Abstract

The small tunneling approximation to the hydrogen-bond-ordering model of ferroelectrics of the KH(2)PO(4) family has been fitted to experimental data for ferroelectrics with composition X Y(2) ZO(4) where X is K, Rb or Cs, Y is the proton or deuteron, and Z is P or As. In almost all cases a quite satisfactory account of the thermodynamic parameters is obtained. the required tunneling parameters are 0, or nearly so, for the deuterated compounds and seem nearly independent of the cation. The hydrogen-bond occupation energy associated with the lowest-energy "disordered" state varies nearly linearly with cation radius for each series of compounds. The results are consistent with the suggestion that the energy parameters of deuterated and nondeuterated materials should scale as the square of the off-center distance.