Donor doping of K0.5Na0.5NbO3 ceramics with strontium and its implications to grain size, phase composition and crystal structureJitka Hreščak
, Goran Dražić
, Marco Deluca
, Iztok Arčon
, Alojz Kodre
, M. Dapiaggi
, Tadej Rojac
, Barbara Malič
, Andreja Benčan
, 2017, original scientific article
Abstract: In this study, the particular effects of A-site donor doping in a lead-free piezoceramic material K0.5Na0.5NbO3 (KNN) doped with Sr2+, i.e., the crystal-structure change, the secondary-phase formation and the grain-size decrease, were investigated. The already-reported causes of these effects upon doping KNN were critically discussed and a mechanism of the effects’ formation was suggested and experimentally supported with advanced analytical methods. Extended X-ray absorption fine structure (EXAFS) analyses proved that the Sr occupies the perovskite A-sublattice, and locally modifies the KNN monoclinic structure to cubic. With the help of Sr K-edge EXAFS and wavelength-dispersive X-ray spectroscopy, the Sr was found to be homogenously distributed in the KNN perovskite lattice with 0.5, 1 and 2% Sr and no Sr segregation on the nano level was found in any of the studied samples with transmission electron microscopy. 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.
Found in: ključnih besedah
Summary of found: ...perovskite, potassium sodium niobate, donor doping, cation vacancies...
Keywords: perovskite, potassium sodium niobate, donor doping, cation vacancies
Published: 17.01.2017; Views: 2812; Downloads: 218
Fulltext (2,11 MB)