Abstract
Surface segregation in metal oxides can greatly influence the oxygen transport and surface oxygen exchange kinetics critical to the performance of solid-state devices such as oxygen permeation membranes and solid oxide fuel/electrolytic cell electrodes. Unfortunately detecting elemental distributions at the atomic scale near the surface remains challenging, which hampers the understanding of underpinning mechanisms and control of surface segregation for the design of high-performance materials. Using the coherent Bragg rod analysis (COBRA) method, we report the first direct 3D atomic imaging of a 4 nm-thick "La0.8Sr0.2CoO 3-δ"/SrTiO3 epitaxial film. Of significance, energy differential COBRA revealed pronounced Sr segregation (La 1-xSrxCoO3-δ, x ∼ 0.4) in the four unit cells from the top surface while complete Sr depletion was detected in the five unit cells from the "La0.8Sr0.2CoO 3-δ"/SrTiO3 interface. The drastic strontium compositional changes in the film were associated with large changes in the atomic positions of apical oxygen sites in the perovskite structure. Such Sr segregation tendencies toward the surface were also found in nominal "La0.6Sr0.4CoO3-δ" thin films, which can greatly enhance the surface oxygen exchange properties of oxides. The results presented here show that COBRA and the differential COBRA methods can be used to investigate a variety of electrochemically active systems providing atomic scale structural and chemical information that can help understand the physical and chemical properties of these systems and serve as a basis for comparison with DFT calculations. © 2014 The Royal Society of Chemistry.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1166 |
| Journal | Energy & Environmental Science |
| Volume | 7 |
| Issue number | 3 |
| DOIs | |
| State | Published - 2014 |
| Externally published | Yes |
Bibliographical note
KAUST Repository Item: Exported on 2020-10-01Acknowledgements: This work was supported in part by DOE (SISGR DESC0002633) and King Abdullah University of Science and Technology. The authors like to thank the King Fahd University of Petroleum and Minerals in Dharam, Saudi Arabia, for funding the research reported in this paper through the Center for Clean Water and Clean Energy at MIT and KFUPM. This research was supported by the Israel Science Foundation under grant no. 1005/11. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract no. DE-AC02-06CH11357. Authors thank the beamline technical support from Zhan Zhang, Christian M. Schlepuetz and Lynette Jirik at ID-33 of APS. The PLD preparation performed was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.