Na0.5Bi0.5TiO3 (NBT) and NBT-based solid solutions are known as ones of the most perspective lead-free ferroelectrics. Although they are widely studied concerning improvement of physical properties, research of role of production procedure is left without sufficient attention. In this work, we present a thorough study of influence of processing on microstructure and chemical content of NBT ceramics, as well as intentionally and non-intentinally created deviations from the stoichiometric composition. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, dielectric spectroscopy and polarization measurements are used as the main techniques for characterization. It is shown that grain size increases upon sintering temperature, with appearing of abnormal grain growth at high temperatures, while porosity has minimal values at approximately 1160°C. Energy-dispersive X-ray analysis reveals presence of Bi-deficient inclusions, which appear due to evaporation of Bi on calcination stage. While, during sintering, reducing of Bi content is not detected – composition of the matrix grains remains highly stoichiometric and concentration of inclusions does not increase. Whereas, thermal treatment of the ceramics at temperatures above 1160°C causes intense evaporation of Bi from the surface and appearance of large concentration of TiO2 inclusions as a consequence. Chemical composition of inclusions appearing in NBT ceramics with excess Bi added during processing contains large concentration of Ti. This rather leads to excess of Na in the NBT matrix grains and not excess of Bi, as it could be expected. Taking into account high stability of NBT regarding deviations from stoichiometry, local chemical composition of NBT-(SrBi) TiO3 solid solutions is studied. The results are also accompanied with studies of involving hot isostatic pressing in the processing of NBT ceramics, helping to improve its density.
Marija Dunce is a leading researcher at the Department of Ferroelectric Materials of the Institute of Solid State Physics, University of Latvia (ISSP UL) in Riga, Latvia, where she works since 2005. Marija Dunce has PhD in Solid State Physics from the University of Latvia. Currently she works in the framework of her post-doctorate research project and investigates influence of production procedure and parameters on NBT and NBT-based lead-free ferroelectric ceramics, involving such ceramics characterization techniques as scanning electron microscopy, energy-dispersive x-ray spectroscopy, x-ray diffractometry and dielectric spectroscopy.
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