Dielectric Relaxation and Electrical Properties of Lead-Free Perovskite BaGex(Fe0.5Nb0.5)1−xO3 Ceramic

The lead-free BaGex(Fe0.5Nb0.5)1−xO3: BGFN ceramics were synthesized by a solid state reaction technique. The BGFN powders were produced via mixed-oxide method with the desired compositions of BaGex(Fe0.5Nb0.5)1-xO3 where x = 0.01, 0.015, 0.02 and 0.025, respectively and subsequently calcined at different temperatures from 1100 to 1200°C for 4 h. The mixtures were pressed in to pellets and sintered at 1200 to 1350°C for 4 h to form dense ceramics. The characteristics, including phase formation, microstructures, dielectric properties and pyroelectric properties were also investigated. It was observed that the Ge4+ cations played an important role on the change of crystal structures and the phase formation of the BGFN phases. The XRD results indicated that the structure of BFN is cubic and transforms to monoclinic when the Ge concentration is over 0.015. Moreover, the higher level of Ge4+ addition caused a reduction of grain size and formation of secondary phases: Ba3Fe2Ge4O14 and BaGeO3. The amount of each phase was depended on the concentration of Ge where the Ba3Fe2Ge4O14 and BaGeO3 phases were found to increase with increasing of x content. This in turn affected their electrical properties where dielectric constant (ϵr) was dominately decreased while the dielectric loss and the pyroelectric properties were greatly improved. The optimum composition for this system was found to be x = 0.01, where the maximum values of dielectric constant (∼12000) with relatively lower dielectric loss (0.95) at 1 KHz and at room temperature were achieved. The change in the pyroelectric coefficient and spontaneous polarization of the BFN ceramic is possibly due to the segregation of Ge4+ at grain boundary, resulting in resistance to domain switching during heating or cooling the sample. This promises a good candidate for the new lead free ceramic for applications in capacitors.