Investigations on Dielectric phase transition behavior of Pb(Fe_0.5-xSc_x)Nb_0.5O₃ Multiferroic Ceramics

Abstract

Phase pure Pb[(Fe₀._5-xSc_x)Nb_0.5]O₃ [x = 0 to 0.5] multiferroic relaxors have been synthesized to study the effect of Sc on dielectric phase tansition. Rietveld refinement of x-ray diffraction patterns confirm that the structure transforms from monoclinic (Cm) to rhomobohedral (R3m) at x = 0.3. Absence of low frequency dielectric response in compositions with low Sc content attributed to interfacial polarizabilty arising due to differences in conductivities of grain and grain boundary. Moreover, value of diffusivity parameter (γ) of high of Sc content compositions is near to 2, confirms relaxor charactertistic of these compositions. However, an essential feature of relaxors i.e., frequency dependent dielectric permittivity as a function of temperature is observed only in x = 0.5 composition [Pb(Sc₀.₅Nb_0.5)O₃ (PSN)]. In addition, ferroelectric phase transition temperature (T_max) increases initially at lower Sc content (upto x ≤ 0.25), and further drops beyond x ≥ 0.3. Such behavior of T_max in these compositions is due to the onset of B’-B” local cation ordering at x = 0.3. High temperature Raman spectra of Pb(Sc₀.₅Nb_0.5)O₃ (x = 0.5) confirm the stability of cation ordering in compositions with high Sc content well above the phase transition temperature.