Advanced characterization of complex metal oxide thin films

Advanced materials such as complex metal oxides (CMO) are nowadays used in various industrial and scientific contexts, due to their particular and sometimes unique properties. In the field of solid state electrochemistry CMOs are nowadays used for numerous applications. Different types of morphologies of such transition metal oxides (dense bulk, porous structure, thin films) are suitable for various device applications including solid oxide fuel cells (SOFCs), solid oxide electrolysis cells (SOECs) or gas sensors. However, electrical properties of such materials (e.g. ionic conductivity, superconductivity, permittivity, ) are closely linked to the CMOs chemical composition. Tailoring properties of such advanced materials is therefore often related to the determination of their elemental composition and to monitor the presence of contaminants or to control concentrations of added dopants as well as to verify their distribution within the samples. Although in the past distinct improvements in the characterization of functional properties of CMO thin films have been made, there are still many open questions dealing with the relation between exact (local) composition and measured electrochemical properties. Within this project, an online-LASIL (Laser Ablation of Solids in Liquid) approach for advanced characterization of CMOs will be developed, which should help to improve the fabrication of CMO thin films with well-defined chemical composition but also to contribute to a better understanding of CMO thin film properties. The proposed research covers the following innovative aspects: Further improvement of the recently presented online-LASIL approach towards enhanced sensitivity, enabling the analysis of minor sample components and trace elements, resulting in a more accurate determination of CMO thin film composition (stoichiometry). Assessment of sample homogeneity by 2D imaging (elemental mapping) of the sample surface. Measurement of depth profiles to identify possible differences in the structure of CMO thin films. Application of the developed procedure for improved analytical characterization of CMO (e.g. SrTiO3 or LaMnO3), examples are chosen such that the results of the chemical analysis can be linked directly to measurements of functional properties. Thus the results may have immediate and direct impact for the understanding and application of the properties of CMO thin films. Investigating the influence of different preparation parameters on CMO composition, enabling further improvements in the fabrication of CMO thin films. The project will be performed at TU Wien (Institute of Chemical Technologies and Analytics), furthermore, two international cooperation partners are involved.

In the field of solid state electrochemistry advanced materials such as complex metal oxides (CMO) are nowadays used for numerous applications. Regardless, whether these materials are used for solid oxide fuel cells (SOFCs) or solid oxide electrolysis cells (SOECs), which belong to the most promising technologies for sustainable energy conversion, the electrical properties of the applied CMOs are closely linked to the composition of the materials. Tailoring the properties of such advanced materials is often related to the determination of their precise elemental composition, the monitoring of present contaminants or the control of added dopant concentrations and their distribution within the samples. Therefore, powerful analytical tools, which fulfil all the needs of modern material research, are necessary. In this project, an analytical technique for improved characterization of CMOs has been established, which combines the advantages of solid sampling approaches with the benefits of conventional liquid sample analysis. Continuous optimization of the proposed online-LASIL approach enabled accurate determination of CMO thin film stoichiometry, not only for bulk analysis but also for spatially resolved investigations such as imaging or depth profile measurements, offering the assessment of even minor deviations in sample homogeneity. In contrast to other solid sampling techniques requires the developed approach only liquid standards for quantitative investigations, thus the measurement of novel materials becomes feasible without the use of matrix matched solid reference materials, which are usually not available for newly developed materials. The analytical techniques established in this project were applied to scientific problems which require detailed chemical analysis of CMOs, in particular the interplay between oxygen exchange kinetics and the defect chemistry of different SOFC materials has been investigated thoroughly. Conducted research could clarify the role of several surface compositional effects on the oxygen exchange kinetics: i) Pt nanoparticles, ii) Pt doping in (La,Sr)FeO3, iii) main transition metal cation (Fe, Ti, Co), iv) lattice contraction, v) surface decoration by acidic and basic oxide atoms, vi) effect of Sulphur poisoning. Moreover, details on the local depletion/enrichment of Li in polarized Li(0.29)La0.57TiO3 solid electrolytes for future all solid-state lithium batteries could be determined. To conclude, with this work it was possible to strongly deepen the mechanistic understanding of the oxygen exchange reaction on mixed conducting electrodes. The obtained results are very relevant for future approaches in improving the oxygen exchange kinetics of fuel and electrolysis cells by either avoiding detrimental surface changes or triggering advantageous changes. Also, in the field of all solid-state batteries the results give clear guidelines with regard to the stability limits of the respective materials.