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Updated: Jul 7, 2026

Resonance Raman Spectroscopy of Extreme Nanowires and Other 1D Systems
Published on: April 28, 2016
Temperature dependence of the Raman bandwidths for the lattice and internal modes in ammonium halides close to the
1Department of Physics, Middle East Technical University, 06531 Ankara, Turkey. hamit@metu.edu.tr
Abstract:
We study here the temperature dependence of our Raman bandwidths for the upsilon(5) lattice modes of NH(4)Cl (T(lambda)=241 K) and NH(4)Br (T(lambda)=235 K) and for the upsilon(2) internal mode of NH(4)Cl close to the lambda-phase transitions. Our Raman bandwidths of those modes are studied using a power-law formula on the basis of the soft mode-hard mode coupled model. From our analysis, we extract the values of the critical exponent beta for the order parameter of the ferro-ordered (NH(4)Cl) and the antiferro-ordered (NH(4)Br) phases. Our beta values are close to zero which exhibits a logarithmic behaviour in the vicinity of the lambda-phase transitions in NH(4)Cl and NH(4)Br. It is indicated here that the ammonium halides (NH(4)Cl and NH(4)Br) undergo a weakly first order or nearly second order phase transition close to the lambda transition point.
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