Pseudo‐Spin Motion in Solid Solutions of the Type of the Type K(H 1− x D x ) 2 PO 4

Within the pseudo‐spin model which includes occupation dependent tunnelling frequencies Γ i , dipole moments μ i , and interactions I ij ∼ μ i t ij μ j , the dielectric susceptibility is obtained by a linearized Bloch equation for ferroelectric solid solutions of the type K(H 1− x D x ) 2 PO 4 . The single site and the Bethe‐Peierls version of CPA are used to solve the disorder problem. Using a suitable set of ingoing parameters the Curie temperature, the spontaneous polarization, the intensity of Raman scattering, and the static susceptibility are calculated for various deuterium concentrations, x , and discussed in relation to experiments.