Processing of Dense Nanocrystalline Zirconia Thin Films by Sol-Gel
- PDF / 770,057 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 18 Downloads / 216 Views
0928-GG16-01
Processing of Dense Nanocrystalline Zirconia Thin Films by Sol-Gel Christoph Peters1, Matthias Bockmeyer2, Reinhard Krüger2, André Weber1, and Ellen IversTiffée1 1 Institute of Materials for Electrical Engineering, University of Karlsruhe (TH), Adenauerring 20b, Karlsruhe, 76131, Germany 2 Fraunhofer Institute for Silicate Research, Neunerplatz 2, Würzburg, 97082, Germany
ABSTRACT Via metal organic deposition (MOD) sapphire substrates were multiple dip-coated with a molecular dispersive 8 mol% Y2O3 doped ZrO2 (8YSZ) sol to prepare dense, crack-free thin films. The thin films were consecutively exposed to a tempering program with several rapid thermal annealing (RTA) steps and a final dwell temperature between 500 °C and 1400 °C for 24 h. Grain growth, phase, stoichiometry and macroscopic density of the thin films were analyzed by XRD and SEM. Grain sizes ranged between a few nanometers in diameter at 500 °C and several hundreds of nanometers at 1400 °C. INTRODUCTION Due to the need of increased life-time and less complicated thermal management a reduction of the operating temperature has been identified as an urging goal in the solid oxide fuel cell (SOFC) community [1]. A reduction of the operating temperature results in an increase of the electrolyte resistance. Therefore, ways have to be found to limit electrolyte losses. Two approaches are pursued. Firstly, the thickness of the electrolyte is reduced. Whereas the concept of electrolyte supported fuel cells (ESC) employs electrolyte thicknesses of 50 to 200 µm, anode supported fuel cells (ASC) use thin film electrolytes with a thickness of 5 to 20 µm. Secondly, the composition and the microstructure of the electrolyte material has a strong influence on the electrolyte conductivity. Tuller [2] suggested that a substantial decrease of the average grain size into the nanometer regime could lead to enhanced ionic conductivity through grain boundary effects. However, contrary results on ionic conductivity in nanocrystalline YSZ have been published by Mondal et al. [3] and Kosacki et al. [4]. To study the influence of grain size effects on the ionic conductivity more thoroughly nanocrystalline yttria doped zirconia (YSZ) thin films with varied grain size distributions have been prepared on sapphire substrates via metal organic deposition (MOD). The presented method is capable of processing large-area high quality films at favorable low cost [5]. Depending on the sol composition and processing parameters the thin film microstructure can be varied between porous (for electrodes or as catalyst support) and dense (for electrolytes and coatings). For the thin films produced in this work a hydrolysis procedure was used to deposit dense, crack-free layers. The samples were analyzed by various methods to ensure the high quality of the films. EXPERIMENTAL Processing of 8YSZ thin films A variety of demands are addressed to a coating sol, such as high yield, low crystallization temperature and good properties in wetting, filming and evaporation to obtain pore- and
Data Loading...
