Raman scattering study of ferroelectric phase transition in ammonium sulphate

The interesting features of the temperature and pressure dependence of the Raman spectrum of ammonium sulphate are discussed with respect to its ferroelectric transition at 223 K. These include, the observation of quasi-elastic wing scattering and rapid line-width broadening of both internal and external phonon modes. A model of the transition based on these and previous results is indicated.