Ab initio simulation and investigation of a novel Ta-doped Zirconia material.

Abstract

Ab-initio materials modelling based on the Density Functional Theory is used to investigate the structural and electronic properties of a novel oxide material obtained by doping zirconium oxide (ZrO2 - zirconia) with Ta atoms. The material may have interesting applications in medical and electronic technologies. The work is motivated and driven by X-Ray Diffraction experiments (XRD), which measure the lattice parameters, atomic positions and space groups of these zirconia-based materials. The actual composition and structure of the powders are not known precisely. The Rietveld fit applied to the XRD data, taken at room temperature and pressure, shows that, by increasing the Ta doping from 0 to 12%, the main structures found in the powder are Monoclinic (P21/c), Orthorhombic (Pca21), and Monoclinic(C2/c) at higher Ta concentration. The calculations are focused on the orthorhombic phase. They provide insight into the thermodynamic and structural stability of the pure and Ta-doped oxides and provide a prediction of the minimum-energy crystal structure of the orthorhombic phase. Moreover the results allow for the characterization of the electronic bands structure of the material and on the effects of the point defects on the electronic properties. In particular, when Ta substitute for a Zr ion forming a point defect, there is the appearance of gap states, which may be of interest for technological electronic applications. The computed results will be useful for interpreting the existing measurements and for prompting new experiments that, on the basis of this new fundamental understanding, may better exploit the most interesting features of this new material.