Dielectric dispersions in ferroelectric KD2AsO4

We have investigated the temperature and frequency dependence of the KDP-isomorphous KD2AsO4 (Curie-temperature T-C=162.5 K) in the polar phase by means of dielectric measurements. In the high temperature paraphase the dielectric susceptibility epsilon(33)(omega) only shows the expected resonance due to the piiezodistortive coupling h(36)-P-3 epsilon(6) in the free energy. In the ferrophase we found four distinct dispersion regimes (D1 - D4) of the dielectric susceptibility within the measuring frequency range from 100 mHz to 1 GHz. Three of them are of a relaxational type, one - the remaining above mentionend dispersion - is of the resonance type. The characteristic frequencies of those dispersions are temperature dependent with different functional behaviour, Very near to the phase transition point at 12 K they can be seperated relatively well: f(1) approximate to 1 Hz, f(2) approximate to 100 Hz, f(3) = f(Res) approximate to 10(5) Hz and f(4) approximate to 10(7) Hz The characteristics of the temperature dependence and evolution of the dielectric strength will be discussed leading to some evidence for the origins of the different dispersions, The dispersion D4 is attributed to the domain wall motion and D3 is clearly shown to be the piezoresonance. A phenomenological theory is briefly outlined for a description of the dispersion D2 which in this approach is attributed to the difference between the isothermal and adiabatic dielectric constant. The origin of the dispersion D1 is unknown but may be connected with the so called 'Domain Freezing'-phenomenon (D4).