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dc.contributor.advisorIrvine, John T. S.
dc.contributor.authorPatabendige, Chami Nilasha Kahakachchi
dc.coverage.spatial175en_US
dc.date.accessioned2012-10-16T14:14:10Z
dc.date.available2012-10-16T14:14:10Z
dc.date.issued2012-03-13
dc.identifieruk.bl.ethos.558104
dc.identifier.urihttps://hdl.handle.net/10023/3181
dc.description.abstractThe well-known lanthanide cuprates exist in two principal forms, T and T´, which behave as p-type and n-type conductors, respectively. In order to understand the structural properties and crystal chemistry from the T to T´ phase, the Nd₁.₈₋ₓLaₓPr₀.₂CuO₄ (NLPCO) system was studied varying the La substitution ratio (0≤x≤1.8) and then characterised using high temperature X-ray powder diffraction. From analysis of the X-ray diffraction patterns obtained at room temperature, there are clearly five distinguishable regions for the NLPCO system. They are, (1) monophasic T´ solid–solution (2) two phase mixture T´ + T´´ (3) monophasic T´´solid–solution (4) two phase mixture T´´ + O and finally (5) monophasic O phase solid–solution. The T´´ form has previously been suggested as an ordered form of T´; however here we show via high temperature X-ray diffraction studies that it is a non-transformable metastable phase formed on quenching of the T phase via an orthorhombically distorted variant. Also neutron diffraction and selected area electron diffraction (SAED) studies confirmed that the T ´´phase is 4- fold Cu coordinated.The structural, magnetic and electrical properties of this NLPCO series have been investigated for the selected compositions using X-ray diffraction, magnetization measurements, thermal analysis and conductivity measurements. The aim of the second half of this work was to discover the basic high temperature electrical characteristics of Nd₂₋ₓPrₓCuO₄ and investigate how this matches with those required for components on the SOFC cathode side to identify which dopant level shows highest conductivity and whether it is stable at different temperatures. The idea was to make a new concept in SOFC cathodes and current collector development, using n-type conductors instead of p- type conductors and to try to produce a high conductivity material which is stable under the chemical and thermal stresses that exist while under load that can be used in cathode or current collector applications. The Nd₂₋ₓPrₓCuO₄ (NPCO) series has been studied over a range of dopant levels (x=0.15 - 0.25) and maximum conductivity of 86.7 Scm⁻¹ has been obtained for the composition where x = 0.25. Also NPCO shows n-type semiconductor behaviour which gives operational advantages when operating at mild oxygen deficiency. AC impedance studies have been carried out on symmetrical cells to investigate the performance of NPCO as a cathode material. These studies mainly focused on polarization resistance and the activation energies of the cells. Low Rp values and low activation energies are obtained for a composite cathode compared to pure cathode material. Two configurations of NPCO as cathode materials were tested, pre-fired and in-siu fired. Pre-fired NPCO exhibited better performance than in-situ fired NPCO. Both in-situ and pre-fired current collecting NPCO still showed lowest activation energies which suggest good catalytic activity. From all of these studies, it is evident that the praseodymium doped neodymium cuprate material shows considerable promise as a potential cathode material for solid oxide fuel cell applications.en_US
dc.language.isoenen_US
dc.publisherUniversity of St Andrews
dc.subjectSOFC cathodeen_US
dc.subjectCupratesen_US
dc.subjectNd₁.₈₋ₓLaₓPr₀.₂CuO₄en_US
dc.subjectXRDen_US
dc.subjectPhase diagramen_US
dc.subjectMeta stableen_US
dc.subjectConductivityen_US
dc.subjectSymmetrical cell testingen_US
dc.subjectNd₂₋ₓPrₓCuO₄en_US
dc.subjectN-type semiconductoren_US
dc.subjectAC impedanceen_US
dc.subjectPolarization resistanceen_US
dc.subjectActivation energyen_US
dc.subjectSAEDen_US
dc.subject.lccQD172.R2P2
dc.subject.lcshRare earth metalsen_US
dc.subject.lcshCopper compoundsen_US
dc.subject.lcshX-rays--Diffractionen_US
dc.subject.lcshSolid oxide fuel cellsen_US
dc.subject.lcshCathodes--Materialsen_US
dc.titleMaterial characterisation, phase transitions, electrochemical properties and possible fuel cell applications of Nd₂₋ₓPrₓCuO₄ and Nd[subscript(2-x-y)] La[subscript(y)]PrₓCuO₄ systemsen_US
dc.typeThesisen_US
dc.contributor.sponsorEngineering and Physical Sciences Research Council (EPSRC)en_US
dc.contributor.sponsorInternational Copper Associationen_US
dc.type.qualificationlevelDoctoralen_US
dc.type.qualificationnamePhD Doctor of Philosophyen_US
dc.publisher.institutionThe University of St Andrewsen_US


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