Influence of non-isovalent ion substitution at A site on microstructure and magnetic properties of Ba(Ti0.3Fe0.7)O3 ceramic

Abstract The (Ba 0.8 K 0.2 )(Ti 0.3 Fe 0.7 )O 3 ceramic was prepared by solid-state reaction, and post-annealed in oxygen ambient. By comparison with Ba(Ti 0.3 Fe 0.7 )O 3 made under identical conditions, the effect of non-isovalent A-site substitution of K + on microstructure and magnetism of as-prepared and annealed Ba(Ti 0.3 Fe 0.7 )O 3 samples was investigated using X-ray diffraction, Mossbauer spectroscopy, vibrating sample magnetometer and iodometric titration. It is found that all samples have a single 6H-BaTiO 3 -type hexagonal perovskite structure without any impurities detected, regardless of A-site K + substitution or annealing. In the as-prepared state, non-isovalent A-site substitution of K + induces the variation in Fe occupational site, resulting in the disappearance of room-temperature ferromagnetism. The super-exchange interactions of Fe 3+ at tetrahedral and octahedral Ti sites determine the paramagnetism of (Ba 0.8 K 0.2 )(Ti 0.3 Fe 0.7 )O 3 . During the O 2 annealing process, the presence of Fe 4+ , an unusual valence for iron, besides Fe 3+ is observed, both distributed over octahedral Ti site. By A-site substitution of K + with a lower valence than Ba 2+ , the charge compensation mechanism is further enhanced, and thus more Fe 3+ ions are oxidized to Fe 4+ in annealed (Ba 0.8 K 0.2 )(Ti 0.3 Fe 0.7 )O 3 . Consequently, the ferromagnetic Fe 4+ –O 2− –Fe 4+ super-exchange interactions are strengthened, which leads not only to a paramagnetism–ferromagnetism transition but also to a higher saturation magnetization compared with annealed Ba(Ti 0.3 Fe 0.7 )O 3 .