Preparation and dielectric properties of Ba((Fe0.5Nb0.5)O3/Al2O3 composite ceramics with core/shell structure

Aluminum oxide (Al₂O₃) coated Ba(Fe_0.5Nb_0.5)O₃ (BFN) particles (abbreviated as BFN/Al₂O₃) were synthesized using a facile chemical method. BFN and BFN/Al₂O₃ ceramic samples were sintered at 1350°C and 1200°C for 3 h, respectively. The microstructure and dielectric properties of Al₂O₃ modified BFN ceramics were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and dielectric measurements. Core/shell structure of BFN/Al₂O₃ composite was achieved and the Al₂O₃ is amorphous while BFN/Al₂O₃ composite powders were treated at 800°C for 2 h. The grain sizes of BFN/Al₂O₃ composite ceramic were obviously smaller than those of pure BFN ceramics. The dielectric constant still maintained a large value, and the temperature stability of the ceramics has been improved significantly with coating Al₂O₃ layer. The dielectric loss of BFN/Al₂O₃ composite ceramics was lower than that of BFN ceramics especially in high temperature range. The enhancement of the insulation intensity of grain boundaries and smaller grain sizes derived from the core/shell structure played important roles to reduce the dielectric loss of the BFN ceramics.