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Mode damping by electrostrictive interaction in a uniaxial ferroelectric
Author(s) -
Roy G. K.,
Das A. N.
Publication year - 1979
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.2220960229
Subject(s) - condensed matter physics , soft modes , phonon , anisotropy , physics , electrostriction , isotropy , ferroelectricity , optics , dielectric , quantum mechanics , piezoelectricity , acoustics
An electrostrictive‐type coupling model is used to study mode damping in the paraelectric phase of a uniaxial ferroelectric with an anisotropic soft‐mode dispersion. Mode linewidths are obtained by solving the phonon Green's function equation of motion in the self‐consistent phonon approximation (SPA). The dominant contribution to the damping comes from the scattering of a soft optic phonon with the absorption or emission of an acoustic phonon. The soft‐mode damping γ s shows a ( T – T 0 ) 1/2 behaviour while, in the isotropic limit, it becomes linearly dependent on temperature. For large anisotropy, the longitudinal acoustic attenuation α 1 ∝ ω 2 ( T – T 0 ) −1/2 X XIn ( T – T 0 ) −1/2 or ω 2 ( T – T 0 ) −1/2 according as the soft‐mode is under or over‐damped in the opposite limit, the corresponding dependences are ω 2 ( T – T 0 ) −1/2 and ω 2 ( T – T 0 ) −3/2 , respectively. If soft‐mode interaction with other modes (e.g. phonon density fluctuations) are considered, γ s becomes nearly temperature‐independent in this case α 1 behaves like ω 2 ( T – T 0 ) −1 which compares favourably with experimental observations on lead germanate where the soft‐mode is overdamped.