Caracterização estrutural e estudo da desordem local em nanopartículas de BaTiO3 dopado com lantânio

Abstract

In this work, the properties structures of nanoparticle of BaTiO3 doped with La lanthanum obtained by the polymer precursors method (Pechini method) were studied. The sample was submitted to thermal analyzes DTA and TG, which showed an endothermic peak with (onset) at 965 ºC, indicating the formation of BaTiO3 phase. The DSC curve showed an endothermic peak at 118 ° C, attributed to the Curie temperature (Tc) for the ferroelectric-paraelectrical phase transition. X-ray diffraction (XRD) analysis through the Rietveld refinement, allowed to determine the structural model of the sample, the lattice parameters and atomic positions. With this, the structure was identified as tetragonal, which is characteristic of the ferroelectric phase of BaTiO3. It was also possible to determine the average size of the crystallites in order of 52 nm, obtained from the profile analysis of the Bragg peaks. The study of the local disorder of the sample was carried out via the Fourier transform of the total scattering function, this technique is known as pair distribution function (PDF). Which allowed to study the structure in a radial distance of 20 Å. The lattices parameters, atomic positions and isotropic temperature factors of the sample were determined. As well as, the distribution of the atomic pair along the radial distance. It was also possible to determine the particle diameter (spdiameter) DPDF = 58 nm when relating the peak attenuation function to the pair distribution function. The vibrational modes of the sample were determined by the Raman scattering analysis, which showed the E (TO) mode around 305 cm-1, characteristic of the ferroelectric-paraelectrical phase transition.