Estudo da estrutura cristalina dos sistemas cerâmicos CaCu3Ti4O12, CaCu3Ti4O12- Cr e CaCu3Ti4O12-Nb por meio do método de rietveld-mem combinado com a análise AIM

Abstract

The copper and calcium titanate, CCTO, ceramic that has a perovskite structure of type ABO3 has been extensively studied due to its high dielectric constant, thus allowing numerous applications as in supercapacitors for microelectronic devices. This characteristic is directly related to its crystalline structure, types of atoms, atomic interactions. There are several methods of synthesis for obtaining CCTO, in particular the method used in this work of synthesis of solid state reaction. The present work aimed to study the interference of the doping chromium and niobium in the crystalline structure of the CCTO, especially in the electronic interactions that occur between the atoms belonging to this system. Therefore, electronic density maps were obtained by the Rietveld method of refinement of crystalline structures from X-ray diffraction data, combined with the maximum entropy method (Rietveld-MEM method). Electronic interactions were analyzed using the quantum theory of atoms in molecules (QTAIM). The X-ray diffraction and dispersive energy X-ray spectroscopy analyzes confirmed the presence of a single phase, the cubic CCTO, of space group Im3, with high crystallinity. It was found that the addition of dopants to the structure of the CCTO generally causes an expansion in the dimensions of the modified unit cells. Topological analyzes of electronic densities suggest that the dopants chromium and niobium replace the titanium ion in the crystalline structure of the CCTO. In addition, the topological analysis of electronic densities, their critical points, gradient vectors and contours, allows us to observe that the electronic interactions between atoms are modified by the presence of dopants.