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Raman scattering from soft modes in barium‐doped lead germanate
Author(s) -
Hosea T. J. C.
Publication year - 1990
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1250211104
Subject(s) - germanate , raman spectroscopy , soft modes , barium , curie temperature , doping , barium fluoride , materials science , ferroelectricity , analytical chemistry (journal) , raman scattering , phase (matter) , phonon , chemistry , condensed matter physics , mineralogy , optics , dielectric , physics , inorganic chemistry , optoelectronics , chromatography , ferromagnetism , nuclear physics , organic chemistry
The Raman spectrum of the soft mode and adjacent low‐frequency A TO modes in pure and barium‐doped lead germanate was measured as a function of temperature, T , through the ferroelectric‐paraelectric phase transition. The barium concentrations studied varied from 2.3 to 6.6%. The Raman spectra were analysed for all the temperatures and dopings by least‐squares fitting of a model response function. In general, the phonon line widths increase with the amount of barium doping whereas the soft frequency decreases. Both the soft optic frequency and the mode strength display Curie‐Weiss behaviour close to the Curie temperature, T c . When they are plotted as a function of T c ‐ T , the various fitted soft‐mode parameters generally behave in a qualitatively similar fashion for the different specimens. However, on a quantitative basis, the agreement is less good, showing that the behaviour of the soft mode does not scale simply as T c ‐ T . This may indicate that the influence of the different polarizabilities of the barium defects is important in lead germanate.