Microstructure, optical and electrical characterizations of nanocrystalline ZnAl2O4 spinel synthesized by mechanical alloying: Effect of sintering on microstructure and properties

Abstract

Nanocrystalline ZnAl2O4 spinel compound has been synthesized by mechanical alloying the stoichiometric mixture of ZnO and α-Al2O3 powders. Required phase is initiated within 1 h of milling and nanocrystalline ZnAl2O4 mixed spinel phase has been obtained after 4 h of milling. Phase transformation from mixed spinel to normal spinel structure occurs through redistribution of cations in tetrahedral and octahedral void spaces after 5 h of sintering at 1173 K. Structure and microstructure characterizations of all milled samples have been carried out by analyzing the respective XRD patterns employing Rietveld's refinement method and HRTEM images. The optical band gap of semiconducting ZnAl2O4 is blue shifted due to the sintering effect. All synthesized samples exhibit PL emissions primarily within the UV region. Both the dc and ac electrical conduction mechanisms have been explained respectively by the hopping transport phenomenon and frequency dependent conductivity behaviour, which obeys the Jonscher power law. A better optical property, enhanced electrical conductivity and low dielectric constant value make the synthesized semiconducting ZnAl2O4 compound suitable for optoelectronic applications.