Damping constant and the relaxation time calculated for the lowest-frequency soft mode in the ferroelectric phase of Cd2Nb2O7

Kiraci A., YURTSEVEN H. H.

OPTIK, vol.127, no.23, pp.11497-11504, 2016 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 127 Issue: 23
  • Publication Date: 2016
  • Doi Number: 10.1016/j.ijleo.2016.09.023
  • Journal Name: OPTIK
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.11497-11504
  • Keywords: Damping constant, Soft modes, Pseudospin-phonon coupling, Cd2Nb2O7, TEMPERATURE-DEPENDENCE, PYROCHLORE CD2NB2O7, RAMAN-SCATTERING, BARIUM-TITANATE, CADMIUM NIOBATE, TRANSITIONS, TC, POLARIZATION, COMPOUND, CERAMICS
  • Middle East Technical University Affiliated: Yes

Abstract

The temperature dependence of the phonon frequency omega(ph) and of the damping constant Gamma(sp) due to pseudospin-phonon coupling of the lowest-frequency soft mode is calculated in the ferroelectric phase near the transition temperature (T-C =196 K) in Cd2Nb2O7. Raman frequency of the soft mode is used as an order parameter which is calculated from the molecular field theory. On that basis, the damping constant is calculated by fitting the expressions from the pseudospin-phonon coupled model and the energy fluctuation model to the observed linewidth from the literature below T-C in Cd2Nb2O7. From our analysis, we find that the molecular field theory is adequate for the soft mode behaviour and that both models are also satisfactory for the divergence behaviour of the damping constant as T-C is approached from the ferroelectric phase in Cd2Nb2O7.