Enhancement of optical, dielectric and transport properties of (Sm, V) co-doped ZnO system and structure-property correlations

Abstract

In this work, V-doped and (Sm, V) co-doped ZnO samples have been synthesized using ball milling method followed by heat treatment. The dependence of structural, optical, electrical and dielectric properties of V:ZnO samples on the Sm doping concentration has been explored. The structural properties have been studied by means of X-ray diffraction (XRD) and Rietveld refinement. Oxidation states of the elements present in the samples are determined using X-ray photoelectron spectroscopy. Raman spectra of the samples further verified the observations obtained from XRD. The crystallite size and microstrain have been estimated from the Williamson-Hall analysis. Microstrain increases from 0.814 × 10−3 to 1.01 × 10−3 with increase in the Sm doping level. The morphology of the grains is significantly affected by the Sm doping. The enhancement of defect density with Sm doping is responsible for the observed red shift (3.29–3.19 eV) in the band gap. The frequency dependence of the dielectric properties has been studied at various fixed temperatures ranging from 25 to 350 °C. The increase in real dielectric constant with dopant content indicates the enhancement of energy storage capacity. The ac conductivity follows Jonscher's power law and it increases up to 1 mol% Sm concentration. Further increase in Sm extent leads to the decrease in ac conductivity. The impedance spectroscopy has been performed to understand electrical behavior of samples and Cole-Cole plots are fitted against the equivalent circuit model. The electrical activation energy values for conduction and relaxation vary in the range: 0.281–0.269 eV and 0.260–0.243 eV, respectively.