LATTICE MODES IN PBHPO4 AND H2C4O4

A microscopic model has been proposed which gives an explanation of th e observed anomalies in the phonon spectra of hydrogen-bonded ferroele ctrics. Using a Green's function technique me have obtained a nonlinea r temperature dependence of the frequencies of the phonon modes in PbH PO4 and H2C2O4 in agreement with the experimental data. The importance of the proton ordering effects, i.e. the pseudo-spin-phonon interacti on on the lattice modes is shown.