Double perovskite cobaltates Ln-barium copper oxide thin films: Fabrication, microstructure, and transport properties
Mixed ionic-electronic conducting (MIEC) materials are of increasing interest owing to their potential and wide applications in various novel devices such as ceramic membranes, ultra sensitive chemical sensor, partial oxidation reactors as well as electrodes in soli4d oxide fuel cells (SOFCs). Surprisingly, even after many decades of study, a consensus still does not exist regarding the factors and kinetic steps that limit the performance of those mixed ionic/electronic conducting materials. This situation is related to the complex and difficult-to-replicate morphology and microstructures of the systems prepared by conventional ceramic and/or thick film processing technologies. The main theme of this thesis is fabrication of epitaxial MIEC thin films with well defined surface morphology and microstructure, and investigation of their novel physical and electrochemical properties.
Highly ionic-electronic conductive oxygen-deficient double perovskite PrBaCo2O5+delta thin films were grown on single crystal (001) MgO, (001) LaAlO3 (LAO) and (110) NdGaO3 (NGO) substrate by pulsed laser deposition. The microstructure and epitaxial nature of the as-grown film are characterized by X-ray diffraction. A strong influence of the planar biaxial strain in the film total conductivity was observed. For the first time, a novel symmetric half cell based on epitaxial multilayer thin film with PrBaCo2O5+delta (PBCO) as cathode material, are fabricated by pulsed laser deposition. We obtained a very low ASR at 605°C, 0.1 O cm2 in pure oxygen and 0.18 O cm2 in air, and very fast surface exchange coefficient (0.006cm/s at 598°C). The lowest Ea measured is 0.232 eV. This values is only about 1/3 of the bulk PBCO electrode, 0.67eV, and is by far the lowest activation energy ever been reported.
Furthermore, we successfully fabricated (LaBa)Co2O 5+delta (LBCO) epitaxial thin film, which demonstrates excellent performance and superior stability in both dry and wet 4% hydrogen/nitrogen environment over a wide range of temperature from 400°C up to 780°C. It shows potential application as oxygen sensor device for harsh environments in future power generation facilities and plants.