Colossal dielectric constants in Sr(Fe_0.5Nb_0.5)_1-<i>_x</i>Mn<i>_x</i>O₃ prepared by a modified solid-state reaction technique

In the present work, the Sr(Fe0.5Nb0.5)1-xMnxO3 powders were synthesized via a molten salt technique. Pure phase perovskite was obtained at 800 °C which was very low compared to previous works prepared by solid state reaction technique (> 1200 °C). XRD analysis for the Sr(Fe0.5Nb0.5)1-xMnxO3 ceramics revealed that the unit cell had an orthorhombic symmetry. Examination of dielectric measurement showed that all ceramic samples exhibited very high dielectric constants (εr,max > 200,000 at 1 kHz). The dielectric data showed that all ceramics exhibited a relaxor like behavior. Loss tangent value tended to decrease with increasing Mn, especially at low temperature range. The obtained loss tangent values were found to be lower than those reported in previous works. Impedance spectroscopy analysis revealed that the relaxor like behavior could be related with bulk grain, grain boundaries and electrode responses, where the samples had a heterogeneous conduction. Type of electrode and applied voltage had strong effects on the dielectric behavior.