Influence of germanium substitution on dielectric and ferroelectric properties of Ba(Fe0.5Nb0.5)O3 ceramics

In this work, the influence of Ge⁴⁺ substitution on dielectric and ferroelectric properties of high dielectric BaFe_0.5Nb_0.5O₃ ceramics was studied. The BGFN powders with a formula BaGe_x(Fe_0.5Nb_0.5)_1-xO₃ where x = 0.01, 0.015, 0.02 and 0.025 were produced via mixed-oxide method and subsequently calcined at 1100-1200°C for 4 h. To form the BGFN ceramics, the resulting powders were pressed into pellets and sintered at various temperatures from 1200 to 1350°C for 4 h in order to obtain the ceramic with maximum density under each condition. The phase formation, microstructure and electrical properties of these ceramics were investigated. It was found that the Ge⁴⁺ substitution played an important role on the change of crystal structures and the phase formation of the BFN ceramics. The appearance of peak shift and peak split in XRD patterns confirmed the structural change from cubic to monoclinic in the ceramic samples at higher Ge⁴⁺ content. The ceramics with x ≥ 0.015 contained three phases of BGFN, Ba₃Fe₂Ge₄O₁₄ and BaGeO₃. The amount of each phase was depended on the concentration of Ge⁴⁺ where the Ba₃Fe₂Ge₄O₁₄ and BaGeO₃ phases were found to increase with increasing x content. It was also found that the higher porosity and smaller grain sizes were found in the BGFN ceramics with higher level of Ge⁴⁺ addition. This in turn affected their dielectric properties where dielectric constant was substantially decreased while the dielectric loss was greatly improved. The optimum composition for this system was found to be x = 0.015, where the maximum dielectric constant (~12282) with lower dielectric loss at room temperature were obtained.