Affiliation:
1. Department of Materials Science, Institute for Multidisciplinary Research, University of Belgrade, Belgrade, Serbia
2. Department for Nanostructured Materials, Jožef Stefan Institute, Ljubljana, Slovenia
3. Department of Materials Chemistry, National Institute of Chemistry, Ljubljana, Slovenia
Abstract
In our recent study (Ribic et al. 2020) we reported the structure of
inversion boundaries (IBs) in Sb2O3-doped ZnO. Here, we focus on IBs that
form in SnO2-doped ZnO. Using atomic resolution scanning transmission
electron microscopy (STEM) methods we confirm that in SnO2-doped ZnO the IBs
form in head-to-head configuration, where ZnO4 tetrahedra in both ZnO
domains point towards the IB plane composed of a close-packed layer of
octahedrally coordinated Sn and Zn atoms. The in-plane composition is driven
by the local charge balance, following Pauling's principle of
electroneutrality for ionic crystals, according to which the average
oxidation state of cations is 3+. To satisfy this condition, the cation
ratio in the IB-layer is Sn4+: Zn2+=1:1. This was confirmed by concentric
electron probe analysis employing energy dispersive spectroscopy (EDS)
showing that Sn atoms occupy 0.504 ? 0.039 of the IB layer, while the rest
of the octahedral sites are occupied by Zn. IBs in SnO2-doped ZnO occur in
the lowest energy, IB3 translation state with the cation sublattice
expansion of ?IB(Zn-Zn) of +91 pm with corresponding O-sublattice
contraction ?IB(O-O) of -46 pm. Based on quantitative HRTEM and HAADF-STEM
analysis of in-plane ordering of Sn and Zn atoms, we identified two types of
short-range distributions, (i) zigzag and (ii) stripe. Our density
functional theory (DFT) calculations showed that the energy difference
between the two arrangements is small (~6 meV) giving rise to their
alternation within the octahedral IB layer. As a result, cation ordering
intermittently changes its type and the direction to maximize intrinsic
entropy of the IB layer driven by the in-plane electroneutrality and 6-fold
symmetry restrictions. A long-range in-plane disorder, as shown by our work
would enhance quantum well effect to phonon scattering, while Zn2+ located
in the IB octahedral sites, would modify the bandgap, and enhance the
in-plane conductivity and concentration of carriers. Keywords
Publisher
National Library of Serbia
Subject
Materials Chemistry,Metals and Alloys,Condensed Matter Physics,Ceramics and Composites
Cited by
5 articles.
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