Vibrational properties of RbNd(WO4)2: high pressure Raman study, structural and phonon calculations

Abstract

RbNd(WO4)2 was investigated by high pressure Raman spectroscopy in the 0.1–12.3 GPa pressure interval. The assignment of modes was made based on lattice dynamics calculations and the results of these calculations helped us to also discuss the high pressure behavior of phonon spectra in this material. Our results show that a double oxygen bridge plays a fundamental role in the vibrational properties of this system. A density functional theory (DFT) calculation of hydrostatic pressure effects on RbNd(WO4)2 was performed in order to understand the effect of internal bond changes on the vibrational properties of RbNd(WO4)2. No pressure induced structural phase transition was observed in the Raman study at room temperature, and the DFT calculation (T = 0 K) is consistent with this result. The anomalous softening of the bridge stretching mode at 770 cm−1 was attributed to the decrease of W–O1–W bond angle with increasing pressure.