Microstructure of nanocrystalline yttria-doped zirconia thin films obtained by sol-gel processing

Nano- and microcrystalline yttria-stabilized zirconia (YSZ) thin films with a dopant concentration of 8.3 +/- 0.3 mol% Y2O3 were prepared with a variation in grain size by two orders of magnitude. A sol-gel-based method with consecutive rapid thermal annealing was applied to fabricate YSZ films, resulting in about 400 nm YSZ on sapphire substrates. The average grain sizes were varied between 5 nm and 0.5 mu m by heat treatment in the temperature range of 650 degrees-1350 degrees C for 24 h. High-resolution (HRTEM) and conventional transmission electron microscopy analyses confirmed specimens-irrespective of the thermal treatment-consisting of cubic (c-)ZrO2 grains with nanoscaled tetragonal precipitates coherently embedded in the cubic matrix. Energy-dispersive X-ray spectroscopy and HRTEM on a large number of specimens yielded a homogeneous yttria concentration within the grains and at the grain boundaries with the absence of impurities, i.e. silica at the grain boundaries