Abstract
Ceria doped with trivalent dopants exhibits nonclassical electrostriction, strong anelasticity, and room-temperature (RT) mechanical creep. These phenomena, unexpected for a ceramic material with a large Young's modulus, have been attributed to the generation of local strain in the vicinity of the host Ce cations due to symmetry breaking point defects, including oxygen vacancies. However, understanding why strain is generated at the host rather than at the dopant site, as well as predicting these effects as a function of dopant size and concentration, remains a challenge. We have used the, evolutionary-algorithm-based reverse Monte Carlo modeling to reconcile the experimental data of extended X-ray absorption fine structure and X-ray diffraction in a combined model structure. By extracting the details of the radial distribution function (RDF) around the host (Ce) and trivalent dopants (Sm or Y), we find that RDF of the first-nearest neighbor (1NN) of host and dopant cations as well as the second-nearest neighbor (2NN) of the dopant are each best modeled with two separate populations corresponding to short and long interatomic distances. This heterogeneity indicates that fluorite symmetry is not preserved locally, especially for the dopant first-and second-NN sites, appearing at surprisingly low doping fractions (5 mol % Sm and 10 mol % Y). Given that Ce rather than dopant sites act as the source of local strain for electrostriction and RT creep, we conclude that the environment around the dopant does not respond to electrical and mechanical excitations, likely because of its similarity to the double fluorite structure which has poor electrostrictive and anelastic properties. The trends we observe in the RDFs around the Ce sites as a function of dopant size and concentration suggest that the response of these sites can be controlled by the extent of doping: Increasing dopant size to increase strain magnitude at the 1NN shell of Ce and decreasing dopant fraction to decrease strain propagation to the 2NN shell of Ce should produce stronger electrostrictive response and RT creep.
| Original language | English |
|---|---|
| Pages (from-to) | 7527-7536 |
| Number of pages | 10 |
| Journal | Inorganic Chemistry |
| Volume | 58 |
| Issue number | 11 |
| DOIs | |
| Publication status | Published - 3 Jun 2019 |
Funding
We thank Adam H. Clark, Huw R. Marchbank, and Prof. Gopinathan Sankar of the Department of Chemistry, University College London, United Kingdom, for providing EXAFS spectra for undoped CeO2. I.L. and A.I.F. acknowledge the NSF-BSF program grant 2015679. A.I.F. acknowledges support by NSF grant DMR-1701747. This work was supported in part by the Israeli Ministry of Science and Technology grant 3-12944. This research is made possible in part by the historic generosity of the Harold Perlman Family. Reverse Monte Carlo simulations were performed on the “LASC” cluster-type computer at Institute of Solid State Physics of the University of Latvia. We also acknowledge the support of the BL2-2 beamline of the Stanford Synchrotron Radiation Light Source (SSRL) through the Synchrotron Catalysis Consortium (U.S. Department of Energy, Office of Basic Energy Sciences, Grant DE-SC0012335). Use of the SSRL, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract DE-AC02-76SF00515. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357.