Micro-Raman scattering study of rare earth molybdate II:: Gd2(MoO4)3

In order to investigate the phase transition mechanism of the rare-earth molybdates, micro-Raman scattering spectra and specific heat of Gd-2(MoO4)(3) have been measured and analyzed by the same method used in Tb-2(MoO4)(3). In the frequency region of internal modes, the spectral shape and peak positions are in good agreement with those of Tb-2(MoO4)(3) over the whole temperature region. This fact indicates that MoO4 molecules in both crystal form the same structure and play the same role in the phase transition mechanism. On the other hand, in the high-frequency region from 1000 to 1300 cm(-1), spectra show a strange behavior. Additional broad modes have been appeared in Tb-2(MoO4)(3) from 230 K to 600 K. However, these modes do not appear in Gd-2(MoO4)(3). Furthermore, in contrast to Tb-2(MoO4)(3), the specific heat of Gd-2(MoO4)(3) dose not show the anomaly at 270 K. The new broad modes of TMO seem to be strongly related to the specific heat anomaly of TMO.