Raman scattering investigation of the structural phase transition in single crystal KDy(WO4)2

The Raman scattering spectrum of a KDy(WO4)2 single crystal has been investigated in the frequency range 3–950 cm−1 at temperatures 2, 5, 25, 80, and 300 K. All 36 vibrational modes predicted by the group-theoretical analysis for the high-temperature phase were detected and their symmetries were determined. The analysis of the temperature behavior of the Raman spectra indicates that the monoclinic symmetry of the crystal remains unchanged upon the phase transition. Low-energy electronic transitions are observed between the levels of the ground multiplet 6H15/2 of the Dy3+ ion split by the crystal field of symmetry C2. It is established that in the region of the first excited Kramers doublet of the Dy3+ ion in the KDy(WO4)2 crystal, the Raman spectrum above the phase transition temperature of 6.38 K contains two lines (11.0 and 13.6 cm−1 at 25 K), while at lower temperatures it contains four lines (9.0, 16.2, 16.6, and 18.6 cm−1 at 2 K). This fact shows the presence of four nonequivalent dysprosium ions in...