LOW-TEMPERATURE ULTRASONIC-ATTENUATION MEASUREMENT IN VERY PURE GOLD POLYCRYSTALS AT MEGAHERTZ FREQUENCIES

The ultrasonic attenuation in a polycrystal gold crystal of purity 99. 999% has been measured at three different frequencies, 5, 10, and 30 M Hz, from 77 to 300 K. Mainly one peak (the dislocation relaxation peak , or Bordoni peak) was observed at 178-174, 186-185, and 237-235 K at 5, 10, and 30 MHz respectively. The highest peak temperature observed was for samples given a low stress (8 MPa) while the lowest was for 13 0 MPa stress. On further increasing the stress to 259 MPa the peak tem perature increases slightly. The present work shows that the peak heig ht decreases as the frequency of measurement increases while it increa ses as the mechanical stress increases. The activation energy and the attempt frequency decrease as the compression deformation to the sampl e increases.