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Long‐Wavelength Phonons in the Different Phases of KNbO 3
Author(s) -
Fontana M. D.,
Kugel G. E.,
Metrat G.,
Carabatos C.
Publication year - 1981
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.2221030123
Subject(s) - tetragonal crystal system , phonon , ferroelectricity , condensed matter physics , soft modes , degenerate energy levels , degeneracy (biology) , phase (matter) , phase transition , symmetry (geometry) , materials science , mode (computer interface) , potassium niobate , raman scattering , raman spectroscopy , physics , optics , quantum mechanics , mathematics , optoelectronics , geometry , bioinformatics , biology , computer science , dielectric , operating system
Raman scattering measurements are made in the tetragonal phase of KNbO 3 . The results are in good agreement with the previous corresponding neutron data, and can be assigned to symmetry species. Comparison of these results to those available in the other phases enables to observe the effect of the phase transformations on the LO–TO splitting and on the degeneracy lifting of each initial cubic mode. It is shown that the lowest frequency F 1u cubic mode is the most affected one by the different cell distortions; at each transition, it splits into “soft” and “stiffened” components; it is the so‐called “ferroelectric” mode which drives the successive phase changes. On the other hand, it is remarkable that the phonons derived from the F 2u “silent” mode are nearly degenerate, even in the ferroelectric phases; it is also the case for the phonons issued from the second F 1u cubic mode. Finally, it is emphasized that the phase transitions in KNbO 3 can be described by a displacive‐type mechanism.