Silver iodine, zinc sulfide, barium chlorate, rock crystal and Rochelle salt give rise radio-frequency absorption lines which are called piezoelectric lines.
The characteristics of piezoelectric lines were investigated by the researchers who had found these lines, and a suggestion on the mechanism was also given by them. However, the origin of the absorption seems to be not completely explained by such mechanism.
In the present experiment, the effects of temperature on the absorption lines of pure Rochelle salt, Rochelle salt including impurity, annomium dihydrogen phosphate and rock crystal were investigated in the frequency ranges from 3 MHz to 40 MHz.