FIR reflectivity, pyroelectric effect and dielectric constant in 8% brominated BCCD

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

Authors

Vieira, LG (Author) Other; Almeida, A (Author) FCUP; Ribeiro, JL (Author) Other; Chaves, MR (Author) FCUP; Klopperpieper, A (Author) Other; Albers, J (Author) Other

Journal

Title: Physica Status Solidi (B): Basic Research

Vol. 204

Pages: 863-876

ISSN: 0370-1972

Publisher: Wiley-Blackwell

Indexing

ISI Web of Knowledge - 4 Citations

Scopus - 3 Citations

Other information

Authenticus ID: P-001-A8K

DOI: 10.1002/1521-3951(199712)204:2<863::aid-pssb863>3.0.co;2-9

Abstract (EN): Betaine calcium chloride dihydrate is known to exhibit a rich number of commensurate and incommensurate phases (k = delta(T)c*) between a room temperature paraelectric phase (Pnma) and a lower temperature ferroelectric phase (Pn2(1)a). Partial bromination of this compound induces important changes in the phase diagram of the material. This work reports recent results of FIR reflectivity, dielectric dispersion and pyroelectric effect measured on 8% brominated BCCD. In agreement with previous Raman results reported by Schaack and coworkers, the FIR. reflectivity (E parallel to b) spectra (20 cm(-1) < omega < 300 cm(-1)) show that the sequence of commensurate and incommensurate phases observed in the pure compound is shifted towards lower temperatures and that the structure remains modulated at lower temperatures (modulation wavenumber delta approximate to 1/4 at T = 20 K). The temperature and frequency dependence of the dielectric constants epsilon(a) and epsilon(b), as well as the behaviour of the pyroelectric coefficient lambda(b) observed along a sequence of thermal cycles with and without a bias field, indicate a progressive deviation from thermal equilibrium and a subsequent freezing of the structure at low temperatures. The experimental results are discussed within the framework of a phenomenological model based on a Landau-type free energy expansion, previously reported to account for the phase transition sequence observed in the pure crystal under a positive hydrostatic pressure.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 14