Origin of giant dielectric constant and magnetodielectric study in Ba(Fe0.5Nb0.5)O3 nanoceramics

• High dielectric constant (∼33,000) with low loss (∼0.45) was found at room temperature.
• Cole–Cole plot analysis confirmed the formation of barrier layers on grain–grain boundary interfaces.
• XANES study confirms the mixed valence state of Fe ion.
• Reporting first time about presence of magnetocapacitance (∼3.4%) in the system.

Lead free Ba(Fe0.5Nb0.5)O3 (BFN) ceramics were synthesized by sol–gel method. X-ray diffraction pattern of the samples at room temperature shows a monoclinic structure. The influence of sintering temperature on microstructure and dielectric properties of BFN ceramics were analysed. Microstructure analysis shows well-grown and dense microstructure in 1200 °C sintered sample exhibiting enhanced dielectric and magnetodielectric properties. We report a very high dielectric constant (∼33,000) with low dielectric loss (∼0.45) at room temperature for 1200 °C sintered sample at 100 Hz frequency. Cole–Cole plot shows that the grain boundary effect (barrier layer formation) is responsible for such a high value of dielectric constant. The sample was also analyzed by Fe K-edge X-ray absorption near-edge structure spectroscopy to obtain the Fe oxidation state. This analysis confirms that Fe ions in BFN ceramics are in mixed valance state (Fe2+/Fe3+). Another interesting feature of BFN ceramics is the appearance of room temperature high magnetodielectric response (3.8%) at 7 kOe magnetic field and 100 Hz frequency.