Effects of doping site and pre-sintering time on microstructure and magnetic properties of Fe-doped BaTiO3 ceramics

The A-site substituted BaTiO3 ceramics were prepared by solid-state reaction via partial substitution of Fe for Ba2+. By comparison with the B-site substituted sample made under similar conditions, the effect of Fe doping site on microstructure and magnetism was investigated using X-ray diffraction, Mössbauer spectroscopy and vibrating sample magnetometer. It is found that A-site substitution can be realized to a certain extent at 7 at% Fe addition, whereas impurities are observed at higher Fe concentrations. In the nominal (Ba0.93Fe0.07)TiO3 sample, the Fe ions are present as Fe2+ and Fe3+, respectively, replacing A-site Ba2+ and octahedral B-site Ti4+ in hexagonal perovskite lattice. The double-exchange Fe2+–O2−–Fe3+ interactions produce ferromagnetism well above room temperature, but the saturation magnetization and the Curie temperature are both obviously lower than those for B-site substitution due to different magnetic exchange mechanisms. In the B-site substituted sample Ba(Ti0.93Fe0.07)O3, the super-exchange interactions between Fe3+ on pentahedral and octahedral Ti4+ sites are responsible for ferromagnetism. These results mean that B-site substitution is a better way for Fe-doped BaTiO3 system to obtain high-Curie-temperature ferromagnetism. Moreover, increasing pre-sintering time can further improve the magnetism of B-site substituted samples, through which the saturation magnetization for Ba(Ti0.93Fe0.07)O3 is enhanced ∼6 times.