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dc.contributor.authorLervik, Adrian
dc.date.accessioned2016-08-21T22:28:40Z
dc.date.available2016-08-21T22:28:40Z
dc.date.issued2016
dc.identifier.citationLervik, Adrian. Structural- and Compositional Investigations of Grain Boundaries in Y-Doped BaZrO3. Master thesis, University of Oslo, 2016
dc.identifier.urihttp://hdl.handle.net/10852/51449
dc.description.abstractProton-conducting electrolytes are candidates for a range of electrochemical applications. The search for one which may operate in the intermediate temperature range of 400-800 °C has been ongoing for a while, and Yttrium-doped BaZrO3 (BZY) have been established as one of the most promising materials. Unfortunately, its highly refractory nature makes processing difficult, and generally results in a small grained polycrystalline material with high areas of highly resistive grain boundaries. The cause of resistive grain boundaries is attributed to the formation of space-charge layers, where negatively charged defects segregate close to the grain boundaries in order to compensate the positively charged grain boundary core. A sample prepared unconventionally using extreme temperatures of 2200 °C overcame the grain boundary problem, but an unanswered question is: what did occur during the high temperature treatment? In this thesis, conventional samples were prepared by the Solid State Reaction (SSR) method and characterised by a range of methods. X-Ray Diffraction (XRD) indicates the presence of two cubic phases with slightly different lattice parameters, and X-ray Photoelectron Spectorscopy (XPS) shows Y situated two different chemical states with a seperation of ~2.6 eV. Energy Dispersive Spectroscopy (EDS) performed in the Transmission Electron Microscope (TEM) shows an enrichment of Y and depletion of Ba at the grain boundaries. These are strong indications that Y also substitutes on Ba site in the structure. The microstructure has grains of ~600 nm and the grain boundaries mostly adapt random configurations. Conductivity measurements by impedance spectroscopy indicates the presence of highly resistive grain boundaries, as the conductivity of grain boundaries is three orders of magnitude lower than that of bulk (0.001 vs. 0.000001 S/cm at 400 °C in wet O2). In the high temperature sample the same degree of Ba depletion is not observed, but Y also segregates to the grain boundaries. The grain boundaries are also more frequently near a Coincident Site Lattice (CSL) type grain boundary; an indication of grain boundary migration during the high temperature treatment. Furthermore, two samples prepared through the Solid State Reactive Sintering (SSRS) method, with Ba non-stoichiometry (x = ±0.02, in Ba_{x}Y_{0.15}Zr_{0.75}O_{3}), have been studied by TEM. The goal was to gain more understanding on how the addition of small amounts of NiO assists in the sintering stage, and how it is distributed in the resulting sample. The results shows that Ni rich phase(s) are present at the grain boundaries and triple points in the Ba rich sample. In the Ba deficient sample no secondary phases are observed, but the Ni content is found to be twice as high at the grain boundaries than in the grain interior (bulk).eng
dc.language.isoeng
dc.subjectCharacterization
dc.subjectGrain Boundaries
dc.subjectCeramic Oxides
dc.subjectElectron Microscopy
dc.subjectComposition
dc.subjectSynthesis
dc.subjectProton Conductor
dc.subjectStructure
dc.titleStructural- and Compositional Investigations of Grain Boundaries in Y-Doped BaZrO3eng
dc.typeMaster thesis
dc.date.updated2016-08-21T22:28:40Z
dc.creator.authorLervik, Adrian
dc.identifier.urnURN:NBN:no-54911
dc.type.documentMasteroppgave
dc.identifier.fulltextFulltext https://www.duo.uio.no/bitstream/handle/10852/51449/8/oppginnlev-d81cda6b-27b4-43e2-b290-af953a1e251aMasteroppgave---Adrian-Lervik---ENDELIG-versjon.pdf


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