Enhanced dielectric characteristics of Ba0.94Bi0.04(Fe0.5Nb0.5)O3 coated with SiO2 and SiO2/Al2O3 over a broad frequency and temperature range

Pure phase of Ba0.94Bi0.04(Fe0.5Nb0.5)O-3 (BBFN) nano-particles were obtained by chemical co-precipitation method. The core-shell structure of BBFN@SiO2 and BBFN@SiO2/Al2O3 particles and the target ceramics were successfully prepared by aqueous chemical coating approach. The microstructures and dielectric properties of BBFN@SiO2 and BBFN@SiO2/Al2O3 were studied. Both the BBFN@SiO2 and BBFN@SiO2 and BBFN@SiO2/Al2O3 samples show significantly decreased dielectric loss and good frequency and temperature stability on relative permittivity. Compared to the rapid decline of relative permittivity of BBFN@SiO2, the synergistic effect of SiO2 and Al2O3 in BBFN@SiO2/Al2O3 ceramics made the relative permittivity of which remains a relatively high level with very low dielectric loss, making it more suitable in colossal permittivity applications. Based on the impedance analysis, the grain boundary effect and IBLC models play the important role for the improvement of dielectric properties of BBFN@SiO2/Al2O3 samples.