Raman scattering study of the phase transition in potassium dysprosium tungstate
Abstract
We have studied the Raman scattering spectrum of crystalline KDy(WO4)2 over the temperature range 2–300°K. Of the 36 Raman active vibrational modes predicted by group theoretical analysis, we have observed 34. No anomalies are observed in the behavior of the phonon spectrum at the phase transition (Tc =10 °K). This leads us to conclude that the phase transition takes place with preservation of the center of inversion and without multiplication of the unit cell volume. At low temperatures two additional lines are observed at frequencies of 10 and 135 cm−1 (T = 77 °K), which are absent in the spectrum of the isomorphic compound KY (WO4)2. These lines are attributed to the electronic transitions of the Dy3+ ion. In a detailed study of the low frequency line near the phase transition we observed a change in its spectral position (an increase of the frequency to 18 cm−1 at T = 2 °K) and its linewidth. All the properties of the behavior of this electronic transition are well decribed in terms of a model of the cooperative Jahn–Teller effect.