Ba0.4Sr0.6(Fe0.5Nb0.5)O3 ceramics with extended giant dielectric constant step and reduced dielectric loss

•The incorporation of Sr(Fe0.5Nb0.5)O3 can significantly reduce the dielectric loss and improve the frequency and temperature stability of the dielectric properties of Ba(Fe0.5Nb0.5)O3.•Impedance complex plane plots concluded that the sample is electrically heterogeneous due to separated low resistive grains by highly resistive grain boundaries.•The substitution of barium by strontium suppressed the mixed-value structure of Fe2+/Fe3+ and improved electron hopping barrier height at low- and high-temperature range, respectively.•The high dielectric constant observed in Ba0.4Sr0.6(Fe0.5Nb0.5)O3 ceramics is mainly due to grain boundary response and the mixed-value structure of Fe2+/Fe3+. Ba(Fe0.5Nb0.5)O3 (BFN) and Ba0.4Sr0.6(Fe0.5Nb0.5)O3 (BSFN) ceramics were synthesized by a solid-state reaction. Dielectric constant of BSFN ceramic indicates weak frequency dependence in the range of 20Hz to 20kHz and better temperature stability in the range from 300 to 450K. The extended giant dielectric constant step and the significantly reduced dielectric loss were obtained in BSFN ceramics. The substitution of barium by strontium suppressed the mixed-value structure of Fe2+/Fe3+ and improved electron hopping barrier height at low- and high-temperature range, respectively. Impedance complex plane plots concluded that the sample is electrically heterogeneous due to separated low resistive grains by highly resistive grain boundaries. The inverse of temperature dependence of the Rg and Rgb was found to obey an Arrhenius law with activation energy of 0.26eV and 0.63eV, respectively. The result strongly indicates that the high dielectric constant observed in BSFN ceramics is mainly due to grain boundary response and the mixed-value structure of Fe2+/Fe3+.