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Soft mode and Debye relaxations in Thiourea
Author(s) -
Khelifa B.,
Delahaigue A.,
Jouve P.
Publication year - 1977
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220830115
Subject(s) - soft modes , ferroelectricity , raman spectroscopy , thiourea , dielectric , reflection (computer programming) , debye , permittivity , relaxation (psychology) , materials science , discontinuity (linguistics) , condensed matter physics , debye model , single crystal , dispersion (optics) , dispersion relation , molecular physics , optics , chemistry , crystallography , physics , mathematics , mathematical analysis , psychology , social psychology , optoelectronics , organic chemistry , computer science , programming language
The infrared reflection spectra of a single crystal of thiourea polarized along the ferroelectric axis [100], are extended up to very low frequencies with the help of ε data obtained by some authors. The whole reflectivity spectrum is fitted with a generalized dielectric constant model at several temperatures. So for the first time all the dispersion parameters of the soft mode (a comparison with Raman data is made) are obtained and the existence of two Debye relaxations is shown. One is attributed to domain wall motion and the other to reorientation of molecules. With the help of a generalized LST relation, it is proved that the discontinuity of ε(0) at 169 K is due to a relaxation process.