Photoacoustic Spectra on the Bi or Pr Doped ZnO Varistors.

Abstract

PA spectra with several sintering temperatures on the Bi doped and Pr doped ZnO varistors were measured using the gas microphone method and compared, where the grain structure was observed by the laser microscope. The PA signals in the long wavelength excitaion light decreased as the sintering temperature increased, although the PA signals were large at the short wavelength region on the all samples. The PA signal intensity seems not to depend on the surface area caused by the grain structure change, but it might also relate to the quality of the sintered samples such as the deep levels or defects in the grain. The Pr doped samples need the higher sintering temperature to get the high quality samples than the Bi doped samples.