IONIC CONDUCTING OXIDE MATERIALS FOR CLEAN ENERGY APPLICATIONS: SYNTHESIS, STRUCTURE AND CONDUCTIVITY
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Typ
Examensarbete för masterexamen
Master Thesis
Master Thesis
Program
Biotechnology (MPBIO), MSc
Publicerad
2013
Författare
Hoque, MD khairul
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
The main intent of the study was to find a suitable material with high oxide ion conductivity or proton conductivity which is chemically stable based on pyrochlore and other complex oxide systems. In particular how acceptor doping increased proton or oxide ion conductivity was examined in this thesis. Another purpose of the study was to investigate how the phase transition and other properties of brownmillerite structure based materials changes in humid condition. In this thesis the following materials were investigated, pyrochlore structure based materials (Nd2-xCaxInMO7-δ where M=Nb,Ta 0≤x≤0.05), brownmillerite structure based materials(Ba2In2-xMO5-δ where M=Ga,Y and 0≤x≤0.85) and the zinc containing complex oxide system R2-xCaxBaZnO5- δ where R=La,Nd ; 0≤x≤0.3. These materials were successfully synthesized by solid state sintering method. Rietveld refinement of X-ray diffraction (XRD) on R2-xCaxBaZnO5- δ confirmed these materials possessed tetragonal structure with I4/mcm space group. Changes in the unit cell parameter with Ca2+ introduction was proven by Rietveld analysis. XRD on hydrated samples proved that these materials were not stable in wet condition. Thermogravimetric analysis (TGA) results showed higher than expected mass losses for this system. The oxide ion conductivity of these materials increased with increase of doping level under dry Argon according to impedance spectroscopy data and the reached a maximum of ~0.01 Scm-1 at 1000 °C. The conductivity was also seen to increase further in dry oxygen, indicating significant p-type (electron hole) conductivity. Brownmillerite structure based materials (Ba2In2-xMO5-δ where M=Ga, Y and 0≤x≤0.85) possessed a structure with Ibm2 space symmetry up to x ≤ 0.5 according to XRD. The unit cell volume expanded with increase of doping (ionic radius Y3+=0,92Å) level and contracted with increase of dopant (ionic radius Ga3+=0, 62Å).PXRD of hydrated Brownmillerite showed a structural transformation from orthorhombic to tetragonal. TGA result confirmed that these materials were fully hydrated. ii Pyrochlore structure based materials (Nd2-xCaxInMO7-δ where M=Nb, Ta 0≤x≤0.05) adopt a cubic structure with Fd-3m space group according to XRD and Rietveld refinement. These materials are not good ionic conductors according to the measured conductivity. In summary this work provides a wider understanding of the influence of the acceptor doping on oxide ion conductivity and/or proton conductivity.
Beskrivning
Ämne/nyckelord
Kemi , Chemical Sciences