Estudo teórico de sistemas ferroelétricos usando Teoria do Funcional de Densidade (DFT)

Abstract

In this work, the electronic properties of pure and modified barium titanate, with perovskite structure (ABO3), considering trivalent rare-earth elements, which presente multifunctional characteristics with potential for practical applications. In particular, the multiferroic characteristics as well as electronic structure, have been studied as a function of the rare-earth content considering the Density Functional Theory (DFT), where the polarization of the electronic spin the the Hubbard potential have been taken into account in order to correct the electron-electron Coulumbians interactions in the partially-filled f orbitals of the rare-earth cations. The electronic properties, such as electronic structure and the states density have been calculated after the optimization of the system by using the minimization condition for the total energy. The band-structure were used in order to determine the spontaneous electric polarization, which is very important to confirm the ferroelectric nature of the crystalline systems. The total magnetization, obtained from the self-consistent calculations, is used for determining the ferromagnetic nature of the studied systems. Results show that the Ba^{2+} substitution by La^{3+}, considering the compensation of the crystalline structure with barium vacancies, induce the ferroelectric properties in the doped system, being those less intense that the pure tetragonal BaTiO3. On the other hand, the Ba^{2+} substitution by partially-filled 4f orbitals rare-earths, leads to the simultaneous presence of the dielectric, ferroelectric and ferromagnetic behavior, being the ferromagnetism promoted by the contribution of the 4f electrons of the rare-earth elements. This later property has been also confirmed from the result of the absorption coefficients (XANES) at the oxygen K-edge. The importance of the obtained results opens new perspectives for additional theoretical and experimental researches from the point of view of their designs and analysis of new materials, as well as revelas potential applications of the studied systems for the electro-electronic industry.