Abstract

Lead-free polycrystalline ceramics of Ba(Fe_0.5Nb_0.5)O₃ and its solid solutions 0.91Ba(Fe_0.5Nb_0.5)O₃-0.09BaTiO₃ (BFN-BT) and 0.91Ba(Fe_0.5Nb_0.5)O₃-0.09SrTiO₃ (BFN-ST) were fabricated by a solid-state reaction process, and their electrical properties were characterized in a broad frequency range (100 Hz to 1 MHz) at a temperature range from 30 to 385°C. The prepared ceramics are single phased with monoclinic structure as confirmed by X-ray diffraction. The microstructure analysis was done by scanning electron microscope. Dielectric response show low temperature dielectric dispersion at low frequency showing space charge phenomena arising due to defects. Existence of sharp transition around (T_c~255°C) and broad transitions around (T_c~205°C) of dielectric constant (ε´) versus temperature is demonstrated in the complex perovskite in BFN-BT and BFN-ST ceramics respectively at different frequencies (10.82, 20.2 and 32.2 kHz). The relaxor property was analyzed by the broadening of the maximum dielectric permittivity as well as its shifting to high temperatures with the variation of frequency measurements. In the pure BFN ceramic, dielectric studies confirmed that the compound do not have dielectric anomaly at different frequencies (10.82, 20.2 and 32.2 kHz) and temperature ranges (30 to 385°C). The frequency-dependent electrical data are also analyzed in the framework of conductivity and impedance formalisms.

Key words: Perovskite oxides, dielectric constant, electrical properties, scanning electron micrographs.