ZnCr₂O₄ Inclusions in ZnO Matrix Investigated by Probe-Corrected STEM-EELS.

Wei Zhan,Lasse Vines,Øystein Prytz,Patricia Almeida Carvalho,Andrey Yurievich Kosinskiy,Klaus Magnus Johansen

doi:10.3390/ma12060888

Abstract

The ZnCr2O4/ZnO materials system has a wide range of potential applications, for example, as a photocatalytic material for waste-water treatment and gas sensing. In this study, probe-corrected high-resolution scanning transmission electron microscopy and geometric phase analysis were utilized to study the dislocation structure and strain distribution at the interface between zinc oxide (ZnO) and embedded zinc chromium oxide (ZnCr2O4) particles. Ball-milled and dry-pressed ZnO and chromium oxide (α-Cr2O3) powder formed ZnCr2O4 inclusions in ZnO with size ~400 nm, where the interface properties depended on the interface orientation. In particular, sharp interfaces were observed for ZnO [23]/ZnCr2O4 [10] orientations, while ZnO [110]/ZnCr2O4 [112] orientations revealed an interface over several atomic layers, with a high density of dislocations. Further, monochromated electron energy-loss spectroscopy was employed to map the optical band gap of ZnCr2O4 nanoparticles in the ZnO matrix and their interface, where the average band gap of ZnCr2O4 nanoparticles was measured to be 3.84 ± 0.03 eV, in contrast to 3.22 ± 0.01 eV for the ZnO matrix.

Highlights

Oxides with spinel structures are scientifically and technologically interesting, with a wide range of applications
The zinc oxide (ZnO) pattern was characteristic of the non-centrosymmetric wurtzite structure, while ZnCr2 O4 crystallized in the antiferromagnetic spinel structure
The refined cell parameters of the ZnO and ZnCr2 O4 can be found in Tables S1 and S2 (Supplementary Materials), respectively

Summary

Introduction

Oxides with spinel structures are scientifically and technologically interesting, with a wide range of applications. Zinc chromite (ZnCr2 O4 ) is a spinel with a direct and wide band gap of ~3.8 eV [1,2], and has been proposed as a material for gas and humidity sensing [3,4,5], as a depollution catalytic material for reactions like the oxidation of hydrocarbons and the oxidative dehydrogenation of hydrocarbons [4,6,7], as a photocatalyst [8,9], and in magnetic applications [10] Combined with another wide band gap oxide such as zinc oxide (ZnO), it has been proposed as a catalyst for the dehydrogenative condensation of glycerol for improving the economics of biodiesel production [11], as a photocatalytic material for wastewater treatment [12], and in gas sensing [13]. An alternative approach is to utilize, for example, a ZnCr2 O4 inclusion embedded in a ZnO matrix where the different

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Results

Conclusion