Temperature dependence of dielectric permittivity in incommensurately modulated phase of ammonium fluoroberyllate

TL;DR

This study investigates how dielectric permittivity in ammonium fluoroberyllate varies with temperature near phase transitions, comparing experimental data with multiple models, and finds the Levanyuk and Sannikov approach provides the best fit.

Contribution

The paper demonstrates that the Levanyuk and Sannikov model more accurately describes dielectric behavior in AFB than traditional models, offering insights into improper ferroelectric phase transitions.

Findings

LS model fits experimental data better than CW, GWC, and PLF models.

Physical reasons for model effectiveness are elucidated.

Temperature dependence of dielectric permittivity is characterized near phase transitions.

Abstract

We study the temperature dependence of dielectric permittivity along the polar axis for ferroelectric ammonium fluoroberyllate (AFB) crystal in the vicinity of its phase transition points. The experimental data within incommensurately modulated phase of AFB is compared with the predictions of phenomenological models known from the literature: the Curie-Weiss (CW) law, the generalized Curie-Weiss (GCW) law, and the models by Levanyuk and Sannikov (LS) and by Prelov\v{s}ek, Levstik and Filipi\v{c} (PLF) suggested for improper ferroelectrics. It is shown that the LS approach describes the temperature behavior of the dielectric permittivity for the AFB crystal better than the CW, GWC and PLF models. The main physical reasons of this situation are elucidated.