Study of lattice dynamics and phase transitions in betaine phosphate by comparison with betaine phosphite via infrared reflectivity spectroscopy

• Type: Article in International Scientific Journal
• Date: 1997

Authors

Santos, ML (Author) FCUP; Almeida, A (Author) FCUP; Chaves, MR (Author) FCUP; Klopperpieper, A (Author) Other; Albers, J (Author) Other; GomesMoreira, JA (Author) Other; Gervais, F (Author) Other

Journal

Title: Journal of Physics Condensed Matter

Vol. 9

Pages: 8119-8134

ISSN: 0953-8984

Publisher: Institute of Physics Publishing

Indexing

ISI Web of Knowledge - 15 Citations

Scopus - 16 Citations

Scientific classification

FOS: Natural sciences > Physical sciences

Other information

Authenticus ID: P-001-ANY

DOI: 10.1088/0953-8984/9/38/016

Abstract (EN): The temperature dependence of infrared reflection spectra of betaine phosphate single crystal is reported for polarizations parallel to the a- and b-axes. The spectra were fitted with the factorized form of the dielectric function. A mode assignment is proposed on the basis of a comparison with the spectra of betaine phosphite and deuterated betaine phosphate. Some very asymmetric phonon lines are observed, and the importance of mode couplings is emphasized. A picture of a tendency towards transverse optical mode softening of the low-frequency spectrum upon approaching either side of the T-2 = 86 K phase transition temperature emerges for the polarization parallel to the b-axis, consistent with the peak observed in the temperature dependence of the dielectric constant. On the other hand, the temperature dependence of the ionic effective charges does not display any appreciable discontinuity at the phase transition, contrary to what is observed at the temperature of the transition to the ferroelectric phase of the parent compound betaine phosphite. This is consistent with the very low level of the spontaneous polarization below T-2 in betaine phosphate. The similarities of the behaviours with those of the compounds of the KDP family are discussed.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 16