Dielectric Anomaly of Ammonium Sulfate at Its Transition Temperature

Dielectric anomaly accompanied by a phase transition of the single crystal of ammonium sulfate was observed at audio and radio frequencies. It was found that a sharp peak appeared in a-axial direction and kinks appeared in b- and c-axial directions and that the transition temperature was -36℃ on cooling and -29℃ on warming. The dielectric constants at room temperature were determined to be 8.0, 7.45 and 6.7 along a-, b- and c-axial directions, respectively. They are independent of frequency between 10 to 10^5 kc/sec. It was also found that the transition temperature of pressed polycrystalline powder specimen was about -53℃, which was much lower than that of single crystal