Temperature-induced isostructural phase transition on NaCe(MoO₄)₂ system: A Raman scattering study

Temperature-dependent Raman spectroscopic study has been performed on scheelite-type sodium‑cerium molybdate - NaCe(MoO₄)₂ - in the temperature range 113-873 K. This study provides phonon properties of NaCe(MoO₄)₂, which are very important to understand the mechanism governing eventual phase transitions undergone by the structure, since phonons are very sensitive to structural changes. The ambient scheelite phase remains stable in a low-temperature range (113-293 K), and no relevant modification is observed in the Raman spectra. However, the experiments reveal the existence of one reversible phase transition at high-temperature. The vibrational spectra of NaCe(MoO₄)₂ system showed anomalies above 748 K, where overlaps of some bands and the appearance of a band at 458 cm^-1 are observed. These modifications were attributed to an isostructural phase transition and a discussion about the possible mechanism of this transformation is furnished.