Variation of the Raman frequency of a soft mode with the pressure (20 oC) for the phase transitions in NH4F

Year 2016, Volume: 17 Issue: 4, 747 - 753, 01.12.2016

Hamit Yurtseven , Zeynep Tuğce Ozkarslıgil Ozlem Tari

https://doi.org/10.18038/aubtda.267109

https://izlik.org/JA35TG42TP

Abstract

The Raman frequency of a soft mode (238 cm^-1)
is analyzed as a function of pressure at 20 ^oC for NH₄F
using the experimental data from the literature. This analysis is performed for
the pressure dependence of the Raman frequency shifts (1/n)(¶n/¶P)_T of the
soft mode close to the I - III, III - V and V – VI transitions in NH₄F.
The frequency shifts increase as the pressure increases toward the phase
transitions at T = 20 ^oC (293 K) in this ammonium structure. From
the frequency shifts of the soft mode studied, the pressure dependence of the
isothermal compressibility is predicted through the mode Grüneisen parameter. Our
calculated isothermal compressibility can be compared with the experimental
measurements.

Keywords

Raman frequency , Soft mode , Phase Transitions , NH4F.

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