Caracterização estrutural e eletrônica da zircônia pura e com defeitos e impurezas / Structural and electronic characterization of zirconia, pristine and with impurities

AUTOR(ES)

Michel Lacerda Marcondes dos Santos

FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

09/12/2011

RESUMO

In this investigation we studied the electronic properties and the structural stabilities of zirconia (ZrO2), as well as oxygen vacancy and Ce substitutional impurity. The investigations were carried by computational simulations using ab initio methods, based on the density functional theory and the APW + lo (Aumengted Plane Waves plus local orbitals) method, as implemented in the WIEN2k code, considering the supercell approach and atomic relaxations. Concerning the ZrO2 bulk, the tetragonal (quasi-cubic) phase is not thermodynamically stable at room temperature, but it can be retained in a metastable condition in nanocrystalline powders with crystallite sizes smaller than a certain critical size, or throught addition of dopants, for example cerium. In this cases, oxygen vacancies are always present. In this work we have obtained the properties of the cubic and tetragonal phases of ZrO2. From the results, we propose that the quasi-cubic structure presented in many articles can be understood as a body centered tetragonal structure, with small oxygen atoms displacement perpendicular to the k direction. Those results suggest that the analysis of the X-ray and EXAFS (Extended X-ray Absorption Fine Structure) data should include in the crystallographic model the body-center tetragonal structure. The results of the structural and electronic properties of the oxygen vacancy suggest that its presence could explain the different models of the Zr first neighbor oxygen shell. For the Ce substitutional impurity, our results present a possible explanation why these impurities, in several concentrations, are able to stabilize the ZrO2 in the tetragonal and cubic phases.

ASSUNTO(S)

estrutura dos sólidos impureza impurities structure of solids zirconia zircônia

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