Dielectric dispersions in ferroelectric KD₂AsO₄

Abstract

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 ϵ₃₃(ω) only shows the expected resonance due to the piezodistortive coupling h ₃₆ P ₃ε₆ 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 mentioned 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 162 K they can be seperated relatively well:

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).