Investigation of acoustoionic and acoustoelectronic interaction in fast ionic conductors

In our contribution we present the acoustoionic interaction study results in piezoelectric mixed ionic-electronic conductors AgI, Ag3SbS3 and Ag3AsS3. The “deformation potential” type of interaction was investigated in Rb4AgI5 crystals, and various polycrystalline and glassy solid electrolytes. The relaxational ultrasonic attenuation peaks and velocity dispersion were observed in temperature dependencies. The attenuation peak height was proportional to the electromechanical coupling constant. The activation energies of ionic conductivity were calculated from ultrasonic data. It was shown, that in DC electric field applied on solid electrolyte the ultrasonic attenuation changes substantially and such behaviour is determined by the increase of electric conductivity in the volume of the crystal. The acoustoelectric current caused by electronic charge carriers was observed in illuminated AgI, Ag3SbS3 and Ag3AsS3 crystals. The sign and mobility of free charge carriers were established from acoustoelectronic voltage measurements. Acoustoelectric current was observed also in these crystals in DC electric field and it was shown that the increase of concentration of free holes is responsible for this phenomenon. The ultrasonic behaviour near superionic phase transitions also is discussed.