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Ferroelectric Transitions in KH 2 PO 4 and KD 2 PO 4 Studied by Infra‐Red Polarized Reflection
Author(s) -
Levin S.,
Pelah I.,
WienerAvnear E.
Publication year - 1973
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.2220580105
Subject(s) - ferroelectricity , curie temperature , spectral line , anharmonicity , phase transition , reflection (computer programming) , analytical chemistry (journal) , nucleation , polarization (electrochemistry) , hydrogen , infrared spectroscopy , materials science , absorption spectroscopy , chemistry , crystallography , condensed matter physics , optics , physics , ferromagnetism , dielectric , optoelectronics , organic chemistry , astronomy , computer science , programming language , chromatography
The polarized infra‐red reflection spectra (250 to 4000 cm −1 ) of single crystals of KH 2 PO 4 and KD 2 PO 4 were measured at various temperatures above and below the ferroelectric Curie temperature. The results were compared with previous absorption measurements and allow better assignment of the infra‐red active modes. The existence of strong coupling between certain PO 4 modes and low frequency hydrogen modes is deduced from the abrupt spectral changes on crossing the ferroelectric phase transition. This coupling results from the extremely anharmonic nature of the potential wells along the hydrogen bonds, as is also demonstrated by the KD 2 PO 4 results. The build‐up of the line strength of the transverse hydrogen mode was related to the establishing of the spontaneous polarization below T c . The two phase transitions observed in the KD 2 PO 4 reflection spectra lead to the conclusion that KH 2 PO 4 crystalline nucleation exists on the surface of KD 2 PO 4 single crystals.