Soft modes at the ferroelectric transition ofK2ZnBr4

Raman spectroscopic investigations of external and internal modes of K2ZnBr4 have been performed in the temperature range between 20 and 300 K. A soft mode of A-symmetry has been observed in the ferroelectric phase. Furthermore, another slightly softening mode has been detected with Bg-symmetry above and B-symmetry below Tc. These results complete former X-ray and dielectric investigations and show that the ferroelectric transition of the title compound is partly of order-disorder and partly of displacive character.