Microstrain and defects in polycrystalline Zn_{1-x}Mg_{x}O (0 <= x <= 0.15) studied by X-ray diffraction, and optical and Raman spectroscopies

TL;DR

This study investigates how magnesium substitution affects the structural, optical, and vibrational properties of polycrystalline ZnO, revealing increased microstrain, reduced crystallite size, and altered optical and Raman features due to defects.

Contribution

It provides a comprehensive analysis combining X-ray diffraction, optical, and Raman spectroscopy to understand defect formation and microstructural changes in Mg-doped ZnO.

Findings

Mg substitution reduces crystallite size and increases lattice microstrain.

Optical band gap and band-edge emission energies increase with Mg concentration.

Mg doping broadens Raman peaks, indicating increased crystal defects.

Abstract

The properties of polycrystalline wurtzite Zn_{1-x}Mg_{x}O (0 <= x <= 0.15) have been studied, by powder X-ray diffraction, including an analysis of the X-ray line-broadening, and by luminescence, absorption, and Raman spectroscopies. We have previously established from synchrotron X-ray difffraction that with increasing Mg-concentration, the c-axis compresses, and the off-center cation displacement within each tetrahedral (Zn,Mg)O_{4} unit decreases. Here we perform a size-strain line-broadening analysis of the XRD peaks, which reveals that the Mg-substitution reduces the coherent crystallite size and also develops the lattice microstrain. The optical properties of the samples have been characterized by diffuse-reflectance spectroscopy and fluorimetry. Both the optical band gap and the band-edge emission energies gradually increase with the Mg-concentration in Zn_{1-x}Mg_{x}O. The Mg-substituted samples show broader band tails near the absorption edge, due to the increase of crystal imperfections. The peak broadening of the E_{2}{high} Raman mode, upon the Mg-substitution, is also ascribed to the phonon shortening lifetime mechanism via crystal defects.