A Raman study of temperature dependence of phonons near the λ -phase transitions in ammonium halides

Abstract

This study gives the temperature dependence of the nonsoft optical phonons in ammonium halides under an Ising pseudo-spin-phonon coupled model which considers the interactions between more than one pseudo-spin and one phonon in these crystals. We have analyzed here qualitatively our observed Raman frequencies and bandwidths for the v5TO(174-cm−1) mode of NH4Cl and for the v5LO(177-cm−1) mode of NH4Br. Our observed Raman data for the ammonium halides (NH4Cl and NH4Br) mostly agree with those predicted from the model considered here.