Microstructure and Electrical Properties of BaFe0.5Nb0.5O3 Doped with GeO2 (1-5 wt.%)

In this work, the effects of GeO2 dopant on the electrical properties of BaFe0.5Nb0.5O3 (BFN) perovskite ceramics were investigated. The BFN powder was prepared by a conventional mixed-oxide method using stoichiometric amounts of BaCO3, Fe2O3 and Nb2O5. Afterward the GeO2 contents, ranging from 1 to 5 wt.%, were added to the calcined BFN powder and mixed via vibro-milling method. The mixtures were pressed and sintered at 1125-1150 degrees C for 4 h to form dense ceramics. We showed that the addition of GeO2 caused a reduction of grain size and formation of secondary phases: Ba3Fe2Ge4O14 and BaGeO3. The maximum densities of these BFN doped with GeO2 ceramics were slightly lower than those of the pure BFN due to the occurrence of pores. We also found that the GeO2 doping could improve the dielectric properties of these ceramics at room temperature (25 degrees C). The 1 wt.% GeO2 doped sample exhibited higher dielectric constant of about 1800 and lower dielectric loss of 0.45 comparing to that of pure BFN. However, the dielectric constant values of these ceramics at high temperature (>25 degrees C) were decreased significantly with the increase of GeO2 concentration. In addition, the GeO2 additive gave a weak ferroelectric behavior, leading to change in the pyroelectric coefficient and spontaneous polarization of the GeO2 doped BFN ceramics.