Self-supported films of CeO1.95 display time-scale dependent elastic moduli, a phenomenon which has been termed the chemical strain effect. In order to probe the possible structural origins of this behavior, extended X-ray absorption fine structure spectroscopy and X-ray diffraction were used. Evidence was found that, although this oxygen deficient ceria appears to maintain the fluorite structure on average, the mean Ce-O bond length is shorter than the mean Ce-oxygen vacancy distance. This finding is consistent with crystallographic data from more strongly reduced ceria in which the oxygen vacancies are ordered. By studying strain induced structural changes, we show that it is possible to relate this lattice distortion to the chemical strain effect. Similar conclusions were previously reached for films of Ce 0.8Gd0.2O1.9. Since the ionic radii of both Gd3+ and Ce3+ are larger than that of Ce4+, we suggest that when cation dopants are larger than the host, ceria compounds containing a high concentration of oxygen vacancies may exhibit elastic anomalies.
Bibliographical noteFunding Information:
I.L. wishes to acknowledge the US–Israel Binational Science Foundation , the Israel Ministry of Science and the Israeli Science Foundation for support. This research is made possible in part by the generosity of the Harold Perlman Family. AIF gratefully acknowledges the support of this work by U.S. DOE Grant No. DE-FG02-03ER15476 . The use of the NSLS beamlines was supported by U.S. DOE Contract No. DE-AC02-98CH10886 . Beamlines X18B and X19A at the NSLS are supported in part by the Synchrotron Catalysis Consortium, U.S. DOE Grant No. DE-FG02-05ER15688 .
- Chemical strain
- Extended X-ray absorption fine structure spectroscopy (EXAFS)
- Gadolinium-doped ceria
- Thermal expansion