Estudo experimental e teórico de propriedades estruturais, ferroicas e multiferroicas de compostos baseados no BiFeO3

Abstract

During the last decade it has devoted considerable attention to the research of perovskite crystals that have multiferroicas properties due to their possible applications in multifunctional devices. In this class of materials highlight the BiFeO3 to present both ferroelectricity and magnetism at high temperatures. One approach to improve the ferroelectric and magnetic properties of BiFeO3 is the synthesis of solid solutions with other ferroelectric materials. In this work we chose to study pure BiFeO3, and solid solutions (0.6) BiFeO3 - (0.4) PbTiO3 doped with lanthanum (La) and (1 - x) BiFeO3 - (x) BaTiO3 these combinations improve the properties ferroelectric, magnetic, changing only the concentrations of the precursors. In this work, different samples were prepared by the techniques of co-precipitation and milling of high energy, starting at prepared samples structures were investigated using different space groups to find the stable structures, In this context, this paper studied the crystal structures of these compounds using combinations of various techniques of structural characterizations. The diffraction techniques X ray with the Maximum Method Entropy to calculate electron densities were used, the neutron diffraction order to investigate the structural and magnetic properties, techniques XAFS (X-ray absorption fine structure) to study the local structure. Soon after, studies were performed first principles of stable structures based on density functional theory (DFT) using the SIESTA software. From this technique we were made analysis of the behavior of structural, electrical and magnetic that system. Finally, we made the analysis of electron densities calculated by MEM and DFT investigating the origin of ferroelectricity, and from the electron densities can see confirm the acting of lone pairs distorting the structure.