Infrared and microwave dielectric response of the disordered antiferroelectric Ag(Ta,Nb)O3 system

Recent progress related to the investigation of infrared and microwave properties of the AgNbO3 and AgTaO3 single crystals and Ag(Ta,Nb)O-3 ceramics is reviewed and discussed with the aid of new crystallographic considerations and symmetry approach. It is shown that optical phonons at any temperature contribute to the permittivity by about 100-200 only and the pronounced dielectric anomalies are due to a submillimetre overdamped excitation related to strong anharmonicities in Nb vibrations (Nb disorder). The best microwave properties near room temperature are achieved for the AgTa0.57Nb0.43O3 ceramic for which the permittivity epsilon' approximate to 380 and the quality Q approximate to 550 at 1.586 GHz with the permittivity temperature coefficient alpha(epsilon) passing through zero at 20 degrees C.