Ultrasonic Absorption Measurements in Single Crystals of Naphthalene and p-Dichlorobenzene

Abstract

The attenuation of ultrasonic waves has been measured in single crystals of naphthalene and p‐dichlorobenzene at frequencies from 5 to 95 MHz for the former crystal, and 5 to 65 MHz for the latter. The absorption coefficients of the crystals were proportional to the square of the acoustic frequency. The change in absorption coefficient for the temperature range from 30°C down to —70°C was very small to about —40°C; a slight decrease was observed below this point. There was no appreciable change in the absorption coefficient within the limit of experimental error, up to a (uniaxial) pressure of 4.25×10⁶ dyn/cm² applied in a direction perpendicular to the direction of propagation of the acoustic wave. From these results, it is concluded that any contributions of dislocation damping and thermal conduction in the crystals to the total acoustic absorption were negligibly small. The sound velocity was determined for these same crystals at room temperature. This velocity was to be found to be a linear function of the temperature, with negative slope, and shows approximately the same temperature coefficient in both cases.