Classical ferroelectriclike behavior of highly orderedPb(Sc1/2Nb1/2)O3studied by dielectric and Brillouin scattering spectroscopy

Abstract

The ferroelectric phase transition behavior in the highly ordered $\mathrm{Pb}(\mathrm{S}{\mathrm{c}}_{1/2}\mathrm{N}{\mathrm{b}}_{1/2}){\mathrm{O}}_{3}$ has been investigated by the dielectric and Brillouin spectroscopy. The dielectric permittivity ${\ensuremath{\varepsilon}}_{r}$ exhibits a sharp maximum without any frequency dispersion at its Curie temperature ${T}_{c}$. In the temperature range far above ${T}_{c}$, it was noted that the dielectric permittivity exhibits a noticeable deviation from the Curie-Weiss law below the characteristic intermediate temperature ${T}^{*}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}500\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which is common to most of the Pb-based oxide perovskite relaxors. Upon cooling, the frequency of the longitudinal acoustic phonon mode exhibits a remarkable softening towards ${T}_{c}$. The relaxation time of the order parameter calculated using the Landau-Khalatnikov approach was determined to be more than one order of magnitude lower than that of the disordered $\mathrm{Pb}(\mathrm{S}{\mathrm{c}}_{1/2}\mathrm{N}{\mathrm{b}}_{1/2}){\mathrm{O}}_{3}$ and is very close to that observed in the paraelectric phase of the classical ferroelectric, $\mathrm{BaTi}{\mathrm{O}}_{3}$. The observed dielectric and relaxation features are qualitatively discussed in terms of the difference in the strength of the random electric fields.