XRD measurement of the room temperature in-plane and out-of-plane d-spacings of the (422) diffraction peak of 11 thin film samples of fluorite Ce0.8Gd0.2O1.9 demonstrates that the zz and xx (=yy) components of the strain tensor for this material are not related via a constant, i.e. the Poisson ratio, as is the case for elastic materials. Rather, these strains are independent. We attribute this behavior to the inelastic character of Ce0.8Gd0.2O1.9 deriving from the chemical strain effect, i.e. the lability of point defect-containing complexes under stress. Chemical strain is dependent on the thermal and mechanical history of the film, and above 200 C, is no longer observed, being transformed into elastic strain and stress. This transformation may compromise the mechanical stability of Ce0.8Gd0.2O1.9 containing devices, which must operate over a broad temperature range. Measurements analogous to those described here can assist in predicting the magnitude of such an effect.
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Acknowledgments I.L. wishes to thank the US-Israel Binational Science Foundation and Minerva Foundation for funding this research. I.L. also wishes to acknowledge the assistance of the Nancy and Stephen Grand Research Center for Sensors and Security. The research is also made possible in part by the generosity of the Harold Perlman Family.
- Chemical strain
- Gd-doped ceria
- Thin films
- XRD-strain measurements