Donor doping of K_0.5Na_0.5NbO₃ ceramics with strontium and its implications to grain size, phase composition and crystal structure

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• 作者：Jitka Hre&scaron ; čak^a ; ^b ; ^{jitka.hrescak@ijs.si} ; Goran Dražić^c ; Marco Deluca^d ; ^e ; Iztok Arčon^f ; ^g ; Alojz Kodre^f ; ^h ; Monica Dapiaggiⁱ ; Tadej Rojac^a ; ^b ; Barbara Malič^a ; ^b ; Andreja Bencan^a ; ^b
• 关键词：Perovskite ; Potassium sodium niobate ; Donor doping ; Cation vacancies
• 刊名：Journal of the European Ceramic Society
• 出版年：2017
• 出版时间：May 2017
• 年：2017
• 卷：37
• 期：5
• 页码：2073-2082
• 全文大小：4007 K
• 卷排序：37

文摘

In this study, the particular effects of A-site donor doping, such as crystal-structure change, the secondary-phase formation and the grain-size decrease, in a lead-free piezoceramic material K0.5Na0.5NbO3 (KNN) doped with Sr2+, were investigated. Extended X-ray absorption fine structure (EXAFS) analyses proved that Sr occupies the perovskite A-sublattice, and locally modifies the KNN monoclinic structure to cubic. Introducing Sr into the A-sublattice, as well as accounting for the charge-compensating A-site vacancies in the starting composition, causes increasing lattice disorder and microstrain, as determined from a Rietveld refinement of the synchrotron X-ray diffraction data. Above 2% Sr the system segregates the A-site vacancies in a secondary phase in order to release the chemical pressure, as revealed by Raman spectroscopy. All these effects result in an increasing number of low-angle grain boundaries that limit the grain growth and finally lead to a significant grain-size decrease.