Four-fold multifunctional properties in self-organized layered ferrite

Four different functional properties at room temperature were found in Ba12Fe28Ti15O84 quaternary ferrite ceramics: a thermoelectric character with a prominent Seebeck coefficient of -400 ?V/K, a strong ferrimagnetic character and weak magnetoresistivity, non-linear dielectric character (tunability) and ferro/piezoelectric response. The complex crystalline structure with a naturally occurring self-organized layered structure was mapped by High Resolution Transmission Electron Microscopy. A n-type conduction was found for optimized samples, consistent with the negative Seebeck coefficient. The presence of magnetic domains with a lateral size ranging from few hundreds of nanometers, up to few microns, extended over several grains indicates a strong intergranular magnetic interaction. Local ferroelectric switching as revealed by piezoresponse force microscopy showed a relatively weak effective piezoelectric coefficient with a remnant value of 0.5 p.m./V and a clockwise cycling direction, which was attributed to an effective negative piezoelectric coefficient. The switching behavior was described as originating from the material's nanoscale layered complexity, with a strong anisotropy of its dielectric and ferro/piezoelectric local properties