Classical ferroelectriclike behavior of highly ordered Pb(S c1/2 N b1/2) O3 studied by dielectric and Brillouin scattering spectroscopy

The ferroelectric phase transition behavior in the highly ordered Pb(Sc1/2Nb1/2)O3 has been investigated by the dielectric and Brillouin spectroscopy. The dielectric permittivity r exhibits a sharp maximum without any frequency dispersion at its Curie temperature Tc. In the temperature range far above Tc, it was noted that the dielectric permittivity exhibits a noticeable deviation from the Curie-Weiss law below the characteristic intermediate temperature T∗=500K, 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 Tc. 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 Pb(Sc1/2Nb1/2)O3 and is very close to that observed in the paraelectric phase of the classical ferroelectric, BaTiO3. The observed dielectric and relaxation features are qualitatively discussed in terms of the difference in the strength of the random electric fields.