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Vibrational spectroscopy of alkaline tungsten oxyfluoride crystals: structure, lattice dynamics, ordering processes, and phase transitions



Raman scattering (RS) and infrared absorption (IR) of ammonium oxyfluoride crystals (NH4)3WO3F3, (NH4)2KWO3F3, and Cs2(NH4)WO3F3are compared. Conformation of the WO3F3 octahedral groups has been established; anomalies have been found close to the transition temperatures in the internal vibrational regions of ammonium and WO3F3 groups. The phase transition in (NH4)3WO3F3 is associated mostly with the ordering of octahedral groups and formation of W[BOND]O···H[BOND]N hydrogen bonds. In (NH4)2KWO3F3 crystal, the transition is not related to the ordering processes; Cs2(NH4)WO3F3 retains its disordered structure down to 10 K. Copyright © 2010 John Wiley & Sons, Ltd.