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Evidence of non‐linear behaviour of soft modes in crystals with KDP structure
Author(s) -
Scarparo M. A. F.,
Katiyar R. S.,
Srivastava R.,
Porto S. P. S.
Publication year - 1978
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.2220900213
Subject(s) - soft modes , raman spectroscopy , condensed matter physics , lattice (music) , quantum tunnelling , coupling (piping) , phase transition , physics , spectral line , low frequency , harmonic oscillator , mode (computer interface) , molecular physics , materials science , optics , quantum mechanics , acoustics , astronomy , computer science , dielectric , metallurgy , ferroelectricity , operating system
The low‐frequency B 2 Raman spectra of KDP, RDP, RDA, and D‐RDA are measured as a function of temperature. The low‐frequency data are fitted to the response function of two coupled harmonic oscillators and of two coupled lattice oscillators. The results show that the overdamped proton tunneling mode softens with temperature as the transition temperature T c is approached. However, the results show that very near T c , the soft mode attains a hard‐core frequency. In view of these results the various models proposed in literature to explain the phase transition in these crystals are critically examined. The nature of the coupling between the two modes is also discussed.