Investigation of Interaction of Hydrogen with Defects in Zirconia

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 (V Zr ). We examine the structure of such configurations and for V Zr -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 V Zr and they rather tend to create bonds with neighboring oxygen atoms. The positron lifetime of the V Zr +1H complex is shorter than that for non-decorated V Zr and positron trapping in V Zr +1H complexes could, in principle, explain experimental lifetime data.

Defect Behaviour in Yttria-Stabilised Zirconia Nanomaterials Studied by Positron Annihilation Techniques

“…Possible reasons for shortening the observed lifetime compared to that calculated for V Zr ′′′′ could be seen in (i) inward relaxation of oxygen anions due to attractive Coulomb force toward the trapped positron, or (ii) the formation of a V Zr ′′′′ complex with an impurity atom, likely hydrogen, which may diminish the open volume associated with the vacancy. Hydrogen effects in Zr9Y single crystal were further investigated by Melikhova et al [11,12]. It was demonstrated by theoretical calculations, involving atomic relaxations and charge transfer effects, that experimental lifetimes in this system may be explained by positron trapping in zirconium vacancies containing a hydrogen atom.…”

“…In this Section, experimental data collected in the present investigations are briefly surveyed. The reader is referred to our publications [6][7][8][9][10][11][12][13][14][15][16][17] for full presentations of the measured data. Microstructure information derived from these data is surveyed in the later in this review.…”

“…Extended theoretical calculations were, therefore, performed as part of the present investigations, including positron binding energies to defects, E b , positron lifetimes, τ c , and momentum distributions of annihilation photons. For a detailed description of these calculations and a full presentation of results, the reader is referred to our earlier publications [7,10,11,12] in which several calculation schemes were also examined. The summary in this Section is confined to the starting points of the calculation schemes and a brief characterisation of theoretical results; the consistency of the experimental results with the calculations is treated in the next Section.…”

“…Over the past five years, a series of PAS investigations on a variety of YSZ-based nanomaterials has been conducted [6][7][8][9][10][11][12][13][14][15][16][17] within the collaboration between Charles Univ. Prague -Physics and Engineering Inst.…”