CALCULATION OF THE DAMPING CONSTANT AND ACTIVATION ENERGY FOR RAMAN MODES IN (NH4)(2)SO4


YURTSEVEN H. H. , KARACALİ H., Kiraci A.

INTERNATIONAL JOURNAL OF MODERN PHYSICS B, vol.25, no.15, pp.2063-2080, 2011 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 25 Issue: 15
  • Publication Date: 2011
  • Doi Number: 10.1142/s0217979211101582
  • Title of Journal : INTERNATIONAL JOURNAL OF MODERN PHYSICS B
  • Page Numbers: pp.2063-2080
  • Keywords: Damping constant, (NH4)(2)SO4, ferroelectric phase, FERROELECTRIC PHASE-TRANSITION, PARAELECTRIC AMMONIUM-SULFATE, DEUTERON MAGNETIC RESONANCE, TEMPERATURE-DEPENDENCE, RELAXATION TIMES, T-LAMBDA, (NH4)2SO4, SCATTERING, CRYSTALS, HALIDES

Abstract

The temperature dependence of the damping constant is calculated for various Raman modes in (NH4)(2)SO4 by the expressions derived from the soft mode hard mode coupling model and the energy fluctuation model. The expressions for the damping constant are fitted to the measured Raman bandwidths and then the activation energies are extracted, which are equal to similar to 0.2 eV for the Raman modes studied. The damping constant of a soft mode is also calculated and the activation energy (similar to 0.1 eV) is deduced in this crystal. Values of the activation energies obtained here, can be compared with the value of k(B)T(C) = 0.02 eV for (NH4)(2)SO4. This indicates that this ferroelectric material undergoes an order disorder transition. It is concluded that the observed behaviour of (NH4)(2)SO4 can be described reasonably by the soft mode hard mode coupling model considered here.