Investigation of Interaction of Hydrogen with Defects in Zirconia
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1216-W07-10
Investigation of interaction of hydrogen with defects in zirconia O. Melikhova 1, J. Kuriplach 1, J. Cizek 1, I. Prochazka 1, G. Brauer 2, and W. Anwand 2 1
Charles University, Faculty of Mathematics and Physics, Department of Low Temperature Physics, CZ-18000 V Holešovičkách 2, Prague, Czech Republic
2
Institut für Strahlenphysik, Forschungszentrum Dresden-Rossendorf, Postfach 510119, D-01314 Dresden, Germany
ABSTRACT In the present work we study theoretically hydrogen incorporated into several positions in the zirconia cubic and tetragonal lattices. These are positions in the interstitial space and in the zirconium vacancy (VZr). We examine the structure of such configurations and for VZr-related defects we also calculate selected positron characteristics in order to assess their capability of trapping positrons. It is shown that hydrogen atoms do not prefer to stay in the center of the largest interstitial space nor of VZr and they rather tend to create bonds with neighboring oxygen atoms. The positron lifetime of the VZr+1H complex is shorter than that for non-decorated VZr and positron trapping in VZr+1H complexes could, in principle, explain experimental lifetime data. INTRODUCTION Zirconia (ZrO2) based materials are currently employed in a wide range of industrial applications (like refractories, grinding, solid oxide fuel cells), and many applications are yet under development. At ambient pressure zirconia exhibits three crystallographic phases: monoclinic, tetragonal and cubic. But many applications require the cubic phase that is not stable below ~1400 C. Therefore, a stabilization of this cubic phase is needed, which is often done by additions of yttria (Y2O3). The resulting material is then called yttria stabilized zirconia (YSZ). Due to stabilization, a large amount of oxygen vacancies (VO’s, charge +2) must be introduced to compensate yttrium ions (Y3+) that are negatively charged with respect to the lattice. Consequently, there are two Y ions per one VO and corresponding defect complexes are denoted as VO-2Y (or YZr' VO YZr' in the Kröger-Vink notation). Thus, structural properties of YSZ materials are closely related to the composition of defects and their structure. Positron annihilation (PA) techniques [1] are sensitive to open volume defects and can certainly help in defect identification in YSZ. The positron lifetime that is often measured in PA experiments depends on the size of defects, i.e. increases with the defect size. But the defect charge state also plays a role and positively charged defects, including oxygen vacancies, repulse positrons and cannot trap them. Conversely, neutral and negatively charged defects may act as positron traps provided that the corresponding positron potential well is deep enough. In the case of the VO-2Y complex, which was considered to be the main positron trap in YSZ [2], our calculations [3] indicate that this complex does not constitute a positron trap (the corresponding positron potential well is not sufficiently deep).
Besides oxygen
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