TEM and DFT Study of Basal-plane Inversion Boundaries in SnO2-doped ZnO

  • Vesna Ribić Department of Materials Science, Institute for Multidisciplinary Research, University of Belgrade
  • Aleksander Rečnik Department for Nanostructured Materials, Jožef Stefan Institute
  • Goran Dražić Department of Materials Chemistry, National Institute of Chemistry
  • Matejka Podlogar Department for Nanostructured Materials, Jožef Stefan Institute
  • Zorica Branković Department of Materials Science, Institute for Multidisciplinary Research, University of Belgrade
  • Goran Branković Department of Materials Science, Institute for Multidisciplinary Research, University of Belgrade

Abstract

In our recent study 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 ΔIB(Zn–Zn) of +91 pm with corresponding O-sublattice contraction ΔIB(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.

Published
2021-05-15
Issue
Vol 53 No 2 (2021)
Section
Articles

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