A number of grain boundary phenomena in ionic materials, in particular, anomalous (either depressed or enhanced) charge transport, have been attributed to space charge effects. Developing effective strategies to manipulate transport behaviour requires deep knowledge of the origins of the interfacial charge, as well as its variability within a polycrystalline sample with millions of unique grain boundaries. Electron holography is a powerful technique uniquely suited for studying the electric potential profile at individual grain boundaries, whereas atom-probe tomography provides access to the chemical identify of essentially every atom at individual grain boundaries. Using these two techniques, we show here that the space charge potential at grain boundaries in lightly doped, high-purity ceria can vary by almost an order of magnitude. We further find that trace impurities (<25 ppm), rather than inherent thermodynamic factors, may be the ultimate source of grain boundary charge. These insights suggest chemical tunability of grain boundary transport properties.
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The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.
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This material is based on work supported in large part by the National Science Foundation under grant no. DMR-1720139 (partial support of S.M.H., partial support of X.X., support for sample fabrication and characterization by impedance spectroscopy and HRTEM). Partial support for X.X. was provided by a Northwestern-Argonne Early Career Investigator Award for Energy Research. Work by C.P. was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division. SEM and HRTEM were performed in the EPIC facility of Northwestern University’s NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (no. NSF ECCS-1542205); the MRSEC program (no. NSF DMR-1720139) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation and the State of Illinois, through the IIN. EDS and electron holography were performed at the Center for Nanoscale Materials, an Office of Science user facility, supported by the US Department of Energy, Office of Science, Basic Energy Sciences, under contract no. DE-AC02-06CH11357. APT was performed at the Northwestern University Center for Atom-Probe Tomography (NUCAPT). The LEAP tomography instrument at NUCAPT was purchased and upgraded with grants from the NSF-MRI (no. DMR-0420532) and ONR-DURIP (nos. N00014-0400798, N00014-0610539, N00014-0910781 and N00014-1712870) programs. NUCAPT received support from the MRSEC program (no. NSF DMR-1720139) at the Materials Research Center, the SHyNE Resource (no. NSF ECCS-1542205), and the Initiative for Sustainability and Energy at Northwestern University.
The authors declare no competing interests.
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Xu, X., Liu, Y., Wang, J. et al. Variability and origins of grain boundary electric potential detected by electron holography and atom-probe tomography. Nat. Mater. 19, 887–893 (2020). https://doi.org/10.1038/s41563-020-0656-1
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