SURFACE-ACOUSTIC-WAVE ATTENUATION IN A BETA-ALUMINA THIN-FILM

The attenuation of surface acoustic waves (SAW) in a beta-alumina thin film prepared by the rf-sputtering method has been measured in the frequency region from 130 to 600 MHz at temperatures from 80 to 300 K. Two types of methods are employed for the measurement of the SAW attenuation, which are termed "air-gap method" and "nonpiezoelectric method," to elucidate the coupling mode between mobile ions and the SAW. In both methods, clear peaks in the temperature-dependence curve of the SAW attenuation are observed, which are responsible for the piezoelectric coupling and the local strain coupling, respectively. The attempt frequency of ion jumps is estimated to be 0.9 x 10(12) s-1. And the activation energy is estimated to be 0.13 eV, which is consistent with the value (0.14 eV) calculated with a paired-interstitialcy mechanism of Na+ ions.