Effect of ZnO addition on the structure, microstructure and dielectric and piezoelectric properties of K0.5Na0.5NbO3 ceramics

Leandro Alfredo Ramajo,Miriam Susana Castro,Jonathan Taub

doi:10.1590/s1516-14392014005000048

Leandro Alfredo Ramajo, Miriam Susana Castro + Show 1 more

Open Access

https://doi.org/10.1590/s1516-14392014005000048

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Abstract

Microstructure, structure and electrical and dielectric properties of ZnO-doped K0.5Na0.5NbO3 (KNN) ceramics were investigated. Powders were obtained by the conventional solid-state method. Samples doped with 0 to 1 mol% of ZnO were sintered at 1125 °C for 2 h. Through XRD spectra, the perovskite structure was detected, in addition to small peaks corresponding to secondary phases. It was also observed that zinc changed the microstructure and grain size of KNN ceramics. The addition of 0.5 mol% of Zn2+ produced a softening effect in the ferroelectric properties of the material, and increased its final density. Conversely, the addition of 1 mol% of Zn2+ reduced the sample densification.

Highlights

From the view of the sustainable development, considerable attention for environment friendly lead-free piezoelectric ceramics has been paid to KxNa1-xNbO3-based ceramics (KNN) in recent years[1,2]
Small peaks associated to the presence of a secondary phase can be assigned to K4Nb6O17 (JCPDS76-0977) resulting from slight changes in stoichiometric ratio due to highly volatile alkaline elements during sintering process
Samples showed slight evolution of the tetragonal (0 0 2) and (2 0 0) diffraction peaks with increasing ZnO content. They attributed this structural evolution to three factors: (i) the incorporation of Zn2+cations into the perovskite structure, (ii) the existence of a phase polymorphism on KNN-based materials composed of a main tetragonal phase and traces of a residual, low temperature orthorhombic phase and (iii) the presence of a secondary phase

Summary

Introduction

From the view of the sustainable development, considerable attention for environment friendly lead-free piezoelectric ceramics has been paid to KxNa1-xNbO3-based ceramics (KNN) in recent years[1,2]. Hot pressing could improve the final density of these ceramics This technique is able to obtain high densities and better properties compared to conventional air-sintered samples, it needs careful investigation and optimization of sintering parameters to result in reproducible and high quality ceramics[8]. Li et al determined that with adding 0.6 mol% of ZnO, the Zn2+ first enters the A-site while higher amounts of Zn2+ substitutes B-site ions when the additive was incorporated in the initial mixture[14] Based on these studies, in this work the effect of the ZnO-doping on the structural and microstructural evolution and its influence on the final properties of K0.5Na0.5NbO3based ceramics is presented. Different contents of Zn2+ were analyzed to provide an alternative approach for lead-free materials development

Experimental

Results and Discussion

Conclusions