Raman Scattering Spectra of K2SeO4

The Raman spectra in potassium selenate single crystal were measured over the temperature range 77∼300 K. The spectra contain components due to internal vibrations of selenate radicals in the frequency region 300∼900 cm -1 , and those due to external lattice vibrations in the region 0∼200 cm -1 . The soft-mode was observed whose frequency decreases as the transition point T 1 (129.5 K) is approached from below. On the basis of these results the relationship between the soft-mode and the phase transition is discussed.