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Far‐infrared spectrum and the soft mode of ferroelectric betaine phosphite
Author(s) -
Koch G.,
Happ H.
Publication year - 1993
Publication title -
annalen der physik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.009
H-Index - 68
eISSN - 1521-3889
pISSN - 0003-3804
DOI - 10.1002/andp.19935050603
Subject(s) - soft modes , far infrared , ferroelectricity , dielectric , amplitude , materials science , reflection (computer programming) , infrared , relaxation (psychology) , condensed matter physics , phase transition , phase (matter) , optics , infrared spectroscopy , nuclear magnetic resonance , physics , optoelectronics , quantum mechanics , psychology , social psychology , computer science , programming language
The far‐infrared reflection spectra of betaine phosphite single crystals in the three crystallographic directions are investigated in the range from 5 to 600 cm −1 at temperatures between 203 and 323 K using a dispersive Fourier spectrometer. The dielectric function is evaluated from the complex amplitude reflection coefficient measured. In the spectrum polarized along the ferroelectric direction a soft mode of relaxation type is observed which accounts for a large part of the relevant static dielectric constant at T c = 210 K. Among the oscillator modes, which generally exhibit normal temperature dependence, there is a heavily overdamped mode at 58 cm −1 , polarized along the crystallographia a 1 axis, with anomalous damping behaviour. The damping constant decreases nearly linearly with temperature up to 323 K which is close to T = 355 K where a second phase transition is known to exist.