Dielectric relaxation and order-parameter dynamics in lawsonite

Abstract

The results of dielectric measurements $(f=10 \mathrm{kHz}--400 \mathrm{MHz})$ of the natural mineral lawsonite are presented in the region of the ferroelectric transition ${(T}_{2}\ensuremath{\approx}124 \mathrm{K}).$ The dielectric behavior is characterized by a small value of the Curie-Weiss constant ${(C}_{\mathrm{CW}}=2220 \mathrm{K})$ typical for order-disorder ferroelectrics. This is consistent with the fact that the origin of ferroelectricity in lawsonite is related to the dynamical ordering of protons. In the paraelectric phase the dielectric dispersion is characterized by a Debye relaxation with a single relaxation time ${\ensuremath{\tau}}_{P}=4.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}(T\ensuremath{-}{T}_{2}{)}^{\ensuremath{-}1}.$ A broadening in the dielectric dispersion occurs in the paraelectric phase only in a narrow temperature range $(\ensuremath{\approx}5 \mathrm{K})$ close to ${T}_{2}$ and can be associated with disordering processes in the lattice affected by large polarization clusters. The dielectric relaxation in the ferroelectric phase includes the order parameter dynamics and the domain wall dynamics. The relaxational domain wall dynamics is characterized by an extremely broad distribution of relaxation times. The characteristic parameters of the dielectric relaxation are determined.