Positron annihilation at planar defects in oxides


Positron annihilation at planar defects in oxides

Kuriplach, J.; Brauer, G.; Melikhova, O.

Transition metal oxides are interesting materials with important prospective applications. Planar defects like stacking faults and grain boundaries are often present in such materials and may affect their properties. In particular, it has been recently shown that a zinc oxide (ZnO) single crystal contain a large amount of stacking faults [1]. Furthermore, nanocrystalline materials based on zirconia (ZrO2) are also frequently studied and their characteristics are significantly influenced by grain boundaries [2]. The planar defects just mentioned exhibit free volumes which, in principle, are detectable using positron annihilation spectroscopy. In this contribution, we present a preliminary theoretical study of positron interaction with planar defects in oxides.
First, we examine several stacking faults (SFs) in ZnO, following their structural investigation presented in [3]. It is found that studied SFs represent rather shallow positron traps with the corresponding positron lifetime exceeding the bulk one slightly only. It might be necessary to consider interactions of SFs with other defects (vacancies, impurities) in order to characterize more precisely their effect on materials’ properties, including positron response.
Second, we perform the case study of the Sigma 5 (310) [001] symmetric tilt grain boundary [4,5] in ZrO2. In this case, positrons also localize at the grain boundary, but such localization is affected by the presence of yttrium (Y3+) ions which are often added to zirconia to improve its mechanical properties. The reason is that Y3+ ions influence the charge state of the grain boundary studied.

[1] W. Anwand et al., J. Appl. Phys. 109, 063516 (2011).
[2] J. Čížek et al., Phys. Rev. B 81, 024116 (2010).
[3] Y. Yan et al., Phys. Rev. B 70, 193206 (2004).
[4] Z. Mao et al., J. Am. Ceram. Soc. 85, 1594 (2002).
[5] T. Oyama et al., Phys. Rev. B 71, 224105 (2005).

Keywords: ZnO; stacking faults; positron annihilation

  • Poster
    Tenth International Workshop on Positron and Positronium Chemistry (PPC-10), 05.-09.09.2011, Smolenice Castle, Slovakia

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Publ.-Id: 16386