The role of oxygen vacancies on the structure and the density of states of iron doped zirconia

TL;DR

This study combines theoretical and experimental methods to investigate how oxygen vacancies influence the structure and electronic properties of iron-doped zirconia, revealing the role of Fe oxidation state and vacancies in phase stabilization and electronic behavior.

Contribution

It provides new insights into the effect of oxygen vacancies on the phase and electronic structure of Fe-doped zirconia using combined DFT simulations and experimental characterization.

Findings

Iron exists as Fe3+ in the films.

Oxygen vacancies promote tetragonal phase formation.

Fe(3p) peak position correlates with vacancy-to-Fe ratio.

Abstract

In this paper we study, both with theoretical and experimental approach, the effect of iron doping in zirconia. Combining density functional theory (DFT) simulations with the experimental characterization of thin films, we show that iron is in the Fe3+ oxidation state and accordingly that the films are rich in oxygen vacancies (VO). VO favor the formation of the tetragonal phase in doped zirconia (ZrO2:Fe) and affect the density of state at the Fermi level as well as the local magnetization of Fe atoms. We also show that the Fe(2p) and Fe(3p) energy levels can be used as a marker for the presence of vacancies in the doped system. In particular the computed position of the Fe(3p) peak is strongly sensitive to the VO to Fe atoms ratio. A comparison of the theoretical and experimental Fe(3p) peak position suggests that in our films this ratio is close to 0.5. Besides the interest in the material by itself, ZrO2:Fe constitutes a test case for the application of DFT on transition metals embedded in oxides. In ZrO2:Fe the inclusion of the Hubbard U correction significantly changes the electronic properties of the system. However the inclusion of this correction, at least for the value U = 3.3 eV chosen in the present work, worsen the agreement with the measured photo-emission valence band spectra.