Ultrasonic attenuation in single crystals of aluminum potassium sulfate dodecahydrate and aluminum ammonium sulfate dodecahydrate as a function of frequency and temperature

Abstract

Because of suggestions that at least some alum crystals may become ferroelectric at low temperatures, and that a ferroelectric crystal would show anomalies in the absorption of sound, the attenuation of 10, 30 and 50 M.c. sound waves has been measured in alum single crystals over the temperature range of 300°K to 4.2°K. Results are available for both longitudinal and transverse waves propagated in the [111] direction. In the temperature region between 160°K and 70°K we have obtained some very large attenuation peaks. For 10 M.c. these peaks have attained values up to 14 DB/CM, with a normal background attenuation of approximately 1 DB/CM. For the case of 30 M.c. and 50 M.c. the peaks are much higher than for 10 M.c. However, due to the limitations on the electronic equipment our measured values were limited to 14 DB/CM. In AlNH4(SO4)2 · 12H 2O the attenuation peak is in the temperature region where both the real and imaginary parts of the dielectric constant become large, possibly indicating that the crystal is ferroelectric. A calculation, using a simple theory for the attenuation of sound waves in a ferroelectric material, gave results in rough agreement with our measured values. The single crystals used in this experiment were grown here at Rice. The procedure for growing alum single crystals is discussed in the appendix.