Research Papers in Physics and Astronomy


Date of this Version

February 1976


Published Phys. Rev. B 13, 1344 (1976). Permission to use.


Lines that overlap from thermal broadening in the room-temperature Raman spectrum of gadolinium molybdate are resolved in the 80°K spectrum. A total of 126 of the possible 201 lines have been resolved. Symmetry assignments are derived from considerations of both point symmetry and polariton dispersion, supported by separate measurements of A1(TO) and A1(LO) spectra. The splitting of the unstable 47 cm-1 room-temperature A1(TO) line into a doublet at 44.5 and 51.5 cm-1, observed previously only in ir absorption, is also observed in these spectra. On heating, the 44.5-cm-1 line remains fixed in frequency whereas the 51.5-cm-1 line broadens and shifts toward lower frequency until, above 210°K, the 44.5-cm-1 line is obscured. Another A1(TO) line, peaking at 83 cm-1 at 80°K, shifts toward lower frequency on heating, reaching 75 cm-1 at room temperature and remaining at that value on further heating up to the transition at 159°C where it becomes Raman inactive. The broadening of the 51.5-cm-1 line in the A1(LO) spectrum is less pronounced so its correlation with the modes of the high-temperature phase can be determined unambiguously. These three lines are suggested to be associated with a system of three coupled modes, whose behavior is discussed, qualitatively, in terms of energy transfer between modes and damping via a two-phonon decay involving an optic phonon of about 44.5 cm-1 and a long-wave acoustic phonon.

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