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 100Hz 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 100Hz frequency.