Preparation, structure and ferroelectric properties of Ba(Fe0.5Nb0.5)O3 powders by sol-gel method

Relaxor-type of ferroelectric material Ba(Fe1/2Nb1/2)O3 were fabricated by a sol-gel technique. The powders of Ba(Fe1/2Nb1/2)O3 heated at temperature greater than 550 °C were crystallized into a perovskite structure containing the pyrochlore phase. A pure perovskite phase was formed as the temperature increased to 850 °C. The activation energy of crystallization of Ba(Fe1/2Nb1/2)O3 is 64.25 kJ/mol calculated from Kissinger's equation. The average grain sizes increased with heating temperature (from 20 nm to 30 nm). The sample sintered at 1250 °C for 3 h, a dielectric constant, εmax′, of ∼20 000 and loss tangent of ∼0.2 were obtained at room temperature. Among the measured temperature, BFN is observed to have higher dielectric constant in room temperature than PMN or PFN. From the hysteresis loops (P-E curve) a large remnant polarization Pr of 0.2 μC/cm2 and coercive field Vc of 5 V/μm were measured. All of the properties clearly show that the BFN is a ferroelectric material.