Enhanced temperature stability of Ba(Fe0.5Nb0.5)O3@SiO2 core-shell structured ceramics

To improve the temperature stability of Ba(Fe0.5Nb0.5)O-3 (abbreviated as BFN) ceramics, the core-shell structure of Ba(Fe0.5Nb0.5)O-3@SiO2 (abbreviated as BFN@SiO2) particles were successfully prepared by aqueous chemical coating approach. The effect of insulating SiO2 layer on the microstructures and dielectric properties of BFN ceramics was investigated. TEM shows that the thin SiO2 layers (about 3 nm) were uniformly and smoothly coated on the surface of BFN particles. The sintering temperature of BFN@SiO2 ceramics was significantly reduced, yet the grain size remains so smaller than that of pure BFN, which attributes to the separation along the grain boundaries of insulating SiO2 layer. It was found that the temperature stability of dielectric constant of the BFN@SiO2 ceramics were significantly enhanced, as TCC (temperature coefficient of capacitance) within +/- 15% was from -55 degrees C to 74 degrees C at 1 kHz and -37 degrees C to 116 degrees C at 10 kHz. Moreover, the room temperature dielectric loss (tan delta) was obviously decreased to 0.18 at 1 kHz and 0.10 at 10 kHz. The reason for the enhanced temperature stability of BFN@SiO2 is that the critical temperature of dielectric relaxation occurred of BFN@SiO2 ceramics moved to lower temperature comparing with pure BFN ceramics, which leads to the dielectric constant step becoming much broader corresponding to the reduction of the activation energy (from 0.298 eV to 0.134 eV). The enhanced temperature stability and reduction of dielectric loss are related to the reduced hopping of charge carriers.