Research Papers in Physics and Astronomy


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Published in Physical Review B Volume 30, Number 9, 1 November 1984. Copyright © 1984 The American Physical Society. Used by permission.


Transmission measurements on Gd2(MoO4)3 in the ( 5-50)-cm-1 region were performed with use of tunable backward-wave oscillator sources (5-30 cm>-1) and a Fourier spectrometer (30-50 cm>-1). The resulting dielectric spectra show an additional low-frequency dispersion which was fitted with a standard central-peak model. Its characteristic relaxation frequency is ~20 cm>-1 and the coupling between the soft mode and central mode increases near the transition temperature. This model also accounts very well for the weak anomaly in the clamped permittivity Ec measured at 63 MHz. The same central mode was used to fit earlier Raman soft-mode spectra. All of these data were fitted with a three-coupled-mode model which revealed that the soft-mode spectrum consists of two strongly coupled bare modes: a higher-frequency mode which softens and carries the entire Raman strength and a lower-frequency mode which is hard (59 cm-1) and Raman inactive. Both of these modes are also coupled to the central mode and this coupling increases sharply near the transition. The relatively large width of the central mode indicates its intrinsic nature and suggests partial disorder near the transition.

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