Ba0.4Sr0.6(Fe0.5Nb0.5)O3 ceramics with extended giant dielectric constant step and reduced dielectric loss
- School of Materials Science and Engineering, Shaanxi University of Science and Technology, Xi’an 710021, China
- Received 4 June 2013
- Revised 10 October 2013
- Accepted 13 October 2013
- Available online 24 October 2013
Dielectric properties of trans-stilbene and p-terphenyl are studied from 1Hz–1MHz.
Dielectric constant and loss spectra show quality and homogeneity of the crystals.
Electronic and molecular relaxation mechanisms were observed in trans-stilbene.
Secondary relaxation mechanisms were not presented in the p-terphenyl crystals.
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 20 Hz to 20 kHz and better temperature stability in the range from 300-450 K. 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 0.26 eV and 0.63 eV, 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+.