As the population rises, it is important that society adopts a more environmentally friendly energy landscape. Currently, solid oxide fuel cells (SOFCs) are a promising technology due to high energy efficiency, power density, and fuel flexibility. However, SOFCs are held back by high costs which are due, in part, to high operating temperatures. It is the principle research goal in the SOFC community to decrease these operating temperatures and current research studies suggest that strain engineering SOFC materials can help. Current studies are hamstrung by the lack of ability to determine stress in-situ thus performance improvements due to strain cannot be isolated. A method to easily measure non-hydrostatic stress is needed to make strain engineered SOFCs a reality. Fluorescent stress sensors have been used to measure non-hydrostatic stress, but the accuracy of these measurements have never been evaluated. The work here uses ruby thin films as non-hydrostatic, fluorescent stress sensors and uses curvature-determined stress to evaluate the accuracy of these new sensors. Highly oriented ruby thin films were deposited onto single crystal sapphire and yttria-stabilized zirconia (YSZ) substrates using pulsed-laser deposition. The resulting ruby/YSZ samples achieved a fluorescence determined stress of 223C1.9 GPa while the ruby/sapphire samples achieved 223C 0.05 GPa. Stress determination from sample curvature measurements confirmed the results of the fluorescence stress measurements, indicating that the ruby piezospectroscopic tensor, which had previously been experimentally validated up to 0.9 GPa, is accurate up to nearly 2 GPa. This work concludes that ruby thin films are an effective sensor for measuring biaxial stress; thus, strain engineering a variety of thin film devices is now a possibility.
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