We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
TEMPERATURE DEPENDENCES OF REFRACTIVE INDICES AND OPTICAL BIREFRINGENCE IN AMMONIUM FLUOROBERYLLATE.
- Authors
HORON, B. I.; KUSHNIR, O. S.; STADNYK, V. YO.
- Abstract
Refractive indices and optical birefringence of improper ferroelectric ammonium fluoroberyllate (AFB) crystals with the incommensurate phase are studied in a wide temperature range. Temperature characteristics of the optical indicatrix of AFB are examined and two quasi-isotropic points are found, the temperature positions T0 of which are almost independent of the light wavelength. Unlike the dielectric permittivity affected by the incommensurate-ferroelectric phase transition (PT) at TC, the optical characteristics of AFB are influenced only by the normal-incommensurate PT located at Ti ≈ 183.1 K. Using a Ginzburg criterion and the experimental Ginzburg number G ≈ 2.5×10-3, we have determined the temperature region around Ti where the critical fluctuations are small and a canonical mean-field theory can be applied. Outside the critical region, the spontaneous birefringence arising due to the incommensurate PT is described perfectly by the Landau theory, with the critical index of the order parameter β ≈ 0.50.
- Subjects
REFRACTIVE index; LANDAU theory; PHASE transitions; BIREFRINGENCE; AMMONIUM; DEBYE temperatures
- Publication
Ukrainian Journal of Physical Optics, 2024, Vol 25, Issue 1, p1020
- ISSN
1609-1833
- Publication type
Article
- DOI
10.3116/16091833/Ukr.J.Phys.Opt.2024.01020