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Title: Layered Ruddlesden-Popper Lan+1NinO3n+1 (n = 1, 2 and 3) epitaxial films grown by pulsed laser deposition for potential fuel cell applications
Author: Wu, Kuan-Ting
ISNI:       0000 0004 5357 0605
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2014
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Layered Ruddlesden-Popper (RP) type La_n+1Ni_nO_{3n+1} (n = 1, 2 and 3) oxides have recently been suggested as candidates for solid oxide fuel cell (SOFC) cathodes. However, the transport properties of the higher order (n = 2 and 3) phases have not been well-understood. The aim of this work is to achieve well-defined epitaxial La_3Ni_2O_{7-δ} and La_4Ni_3O_{10-δ} films deposited by the pulsed laser deposition (PLD) technique in order to fundamentally investigate their intrinsic anisotropic properties for SOFC applications. This research involved PLD target synthesis and PLD deposition for these RP materials. The obtained films were evaluated through crystallographic, compositional, surface morphological and microstructural characterisation. Their electrical, oxygen diffusion and surface exchange properties were characterised by 4-point DC van der Pauw and the isotopic exchange depth profile (IEDP) with secondary ion mass spectrometry (SIMS) method. Finally, the surface and interface information were also obtained via SIMS and low energy ion scattering (LEIS) techniques. An effect of target degradation during deposition was found to have significant influence on the microstructural and compositional variation with increasing film thickness. Successful epitaxial growth of the higher order phases (n = 2 and 3) of lanthanum nickelate have been demonstrated by PLD for the first time. The total planar electrical conductivity of these higher order RP epitaxial films exhibits a more promising conductivity value than La_2NiO_{4+δ}. These dense higher order RP epitaxial films enabled the first information about the oxygen diffusion and surface exchange properties along the c-axis to be obtained. Also, an outermost surface structure of LaO-termination, followed by a Ni-enrichment in the sub-surface region for these RP materials was found by LEIS analysis. These studies provide useful information to help the further development of these materials and related RP-phases for the potential SOFC applications in the future.
Supervisor: Skinner, Stephen; Kilner, John Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral