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Local structure analysis of solid state ionic conductors, perovskite-derived structures by NMR and computational studies 10.17863/CAM.16294 Dervisoglu, Riza In this work, local environments of ions in solid oxide fuel cell (SOFC) electrolyte materials with perovskite and perovskite-derived crystallographic structures, i.e. $Ba_{2}In_{2}O_{5}$, $Ba_{2}(In_{1-x}Ga_{x})_{2}O_{5}$ and $Ba_{2}In_{2}O_{4}(OH)_{2}$, were investigated for their high ionic (O2– and H+) mobility at elevated temperatures. Two general methods were employed in this investigation; first, computational methods, such as density functional theory (DFT), gauge including projector augmented wave (GIPAW), cluster expansion (CE) and Monte Carlo simulations (MC); second, experimental methods, such as nuclear magnetic resonance (NMR), X-ray scattering (both powder diffraction and pair distribution function (PDF) analysis) and thermo-gravimetric analysis (TGA). The parent material, $Ba_{2}In_{2}O_{5}$, has inherent oxygen vacancies which allow for fast O2– ion mobility at elevated temperatures and for hydration of the material needless of doping. We improve a previous NMR study of $Ba_{2}In_{2}O_{5}$ by Adler et al. [1], assigning all three oxygen crystallographic sites to their relevant NMR peaks and investigate the high temperature structure. We then study the iso-valent doping of Ga into the In site resulting in Ba2(In1-xGax)2O5. While Yao et al. [2] find that Ga doping levels higher than 20% form a stable cubic structure, our findings indicate that Ga doping results in a phase segregation. However our findings for quenched samples are no different than those of Yao et al. [2]. Lastly we study the hydrated form of the parent material, $Ba_{2}In_{2}O_{4}(OH)_{2}$, which has high H+ ion mobility above 180C. We observe at least three possible hydrogen sites with local environments slightly different from the previous neutron diffraction study by Jayaraman et al. [3]. In contrast to the observation by Jayaraman et al. [3] of the hydrogen presence in all O2 layers we find an alternating occupancy of hydrogens in those layers. University of Cambridge 2013-10-08 Thesis Doctoral Doctor of Philosophy (PhD) en https://www.repository.cam.ac.uk/handle/1810/245072 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/07a24900-102b-4163-8aab-52249950ca54/download 835269bda140c10400fe0606a14c3d21 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/b6ad100a-d6b7-4d48-9cf0-dd38b92418ca/download c794476dccb0fab3fc9731f56f07ff96 https://www.rioxx.net/licenses/all-rights-reserved/