The Lower Frequency Soft-Mode in the Ferroelectric Phase of K₂SeO₄

Abstract

In the ferroelectric phase below T 3 (93 K) of K 2 SeO 4 a new soft-mode, belonging to the B 2 representation, has been observed by means of Raman scattering experiment. This mode is different from the soft A 1 mode previously reported to soften as T 2 (129.5 K) was approached from below. The frequency of this newly observed mode is abotut 13.2 cm -1 at 9.8 K, and decreases as the temperature increases. The observed result is discussed in connection with the successive phase transitions in the K 2 SeO 4 crystal.