Effects of Transverse and Longitudinal Nonuniformities in Conductivity on Ultrasonic Propagation in CdS

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Abstract
Ultrasonic propagation in piezoelectric crystals as a function of conductivity and electric field has been theoretically described by White. Deviations from the theory are frequently encountered in materials such as CdS, and explanations in terms of trapping, transducer misalignment, dielectric relaxation effects, and nonuniformities in conductivity have been invoked. In this paper the effects of conductivity variations along (longitudinal) and perpendicular (transverse) to the direction of sound propagation on ultrasonic attenuation and amplification characteristics are considered. It is assumed that White's theory is valid locally. The effects of conductivity inhomogeneities are shown to be significant even for relatively small departures from uniformity. Longitudinal variations are especially important, because the electric field required to produce zero attenuation, which is frequently used for determining drift mobilities, shows a considerable variation with measured sample conductivity. A discussion in terms of experimental observations is presented.