Longitudinal relaxation of ND4D2PO4 type antiferroelectrics. Piezoelectric resonance and sound attenuation

Within the framework of the modified proton model with taking into account the interaction with the shear strain ε6, a dynamic dielectric response of ND4D2PO4 type antiferroelectrics is considered. Dynamics of the piezoelectric strain is taken into account. Experimentally observed phenomena of crystal clamping by high frequency electric field, piezoelectric resonance and microwave dispersion are described. Ultrasound velocity and attenuation are calculated. Character of behaviour of attenuation in the paraelectric phase and the existence of a cut-off frequency in the frequency dependence of attenuation are predicted. At the proper choice of the parameters, a good quantitative description of experimental data for longitudinal static dielectric, piezoelectric and elastic characteristics and sound velocity for ND4D2PO4 and NH4H2PO4 is obtained in the paraelectric phase.