Dielectric and Raman investigations of structural phase transitions in (C2H5NH3)2CdCl4

Abstract

Temperature-dependent Raman and dielectric measurements have been carried out on (C₂H₅NH₃)₂CdCl₄ single crystals. Raman studies reveal the presence of two structural phase transitions below room temperature at 216 K and 114 K. The phase transitions are marked by anomalies in temperature dependence of wave-number and full width half maximum (FWHM) of several vibrational modes. The transitions are also accompanied by anomalies in dielectric measurements. Raman and dielectric data indicate that the transition at 216 K is order–disorder in nature and is driven by re-orientation of organic ions, while the transition at 114 K is due to coupling between the CdCl₆ octahedron and the organic chain. Further high temperature dielectric measurements reveal the presence of one more structural phase transition around 473 K across which dispersion in dielectric parameters is observed. The activation energies and relaxation time obtained for high temperature dielectric phases are characteristic of combined reorientation motions of alkyl ammonium cations.