Microstructure–property relationship in textured ZnO-based varistors

Ozer, I. O.; Suvacı, Ender; Bernik, Slavko

doi:10.1016/j.actamat.2010.04.003

Cited by 19 publications

(1 citation statement)

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“…Nonohmic properties of ZnO ceramics with a complex metal-oxide additions attracted researchers already 50 years ago for its use in varistor applications [1]. Successive studies were discovering new additives [2,3] and processing methods [4] to improve varistor's properties. The first to investigate the role of Sn addition in ZnO varistor ceramics were Gould and Carter [5], who recorded power-law dependence of current density on applied voltage, which they interpreted in terms of space-charge-limited conduction controlled by an exponential distribution of traps.…”

Section: Introductionmentioning

confidence: 99%

TEM and DFT study of basal-plane inversion boundaries in SnO2-doped ZnO

et al. 2021

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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

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