Colossal relative permittivity and low dielectric loss in BaFe0.5Nb0.5O3 ceramics prepared by spark plasma sintering

BaFe0.5Nb0.5O3 (BFN) ceramics has been prepared using a rapid process where the powder was synthesised using mechanical milling of the components then consolidated by spark plasma sintering (SPS) for 5 min at 1100 ?C. Xray diffraction results confirmed the pure cubic phase of the prepared SPS BFN ceramic. The average grain size as measured by SEM analysis was similar to 300 nm. Complex impedance measurements revealed giant dielectric constant (epsilon ' similar to 2.3 x 10(4)) and low dielectric loss (tan delta similar to 0.48) for the SPS BFN ceramic at room temperature and 1 kHz. Two thermally activated relaxation peaks were observed in the spectra of imaginary part of modulus (M ''). These relaxations were attributed to the Debye-like relaxation process in grains (at high frequency and low temperature) and non-Debye Maxwell-Wagner (M-W) polarization effect at grain-boundary (at low frequency and high temperature).