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Paving the way to nanoionics: atomic origin of barriers for ionic transport through interfaces

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Frechero, M. A. and Rocci, Mirko and Sánchez Santolino, Gabriel and Salafranca, Juan and Schmidt, Rainer and Díaz Guillén, M. R. and Durá, O. J. and Rivera Calzada, Alberto Carlos and Varela del Arco, María and Santamaría Sánchez-Barriga, Jacobo and León Yebra, Carlos (2015) Paving the way to nanoionics: atomic origin of barriers for ionic transport through interfaces. Scientific reports, 5 . ISSN 2045-2322

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Official URL: http://dx.doi.org/10.1038/srep17229


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Abstract

The blocking of ion transport at interfaces strongly limits the performance of electrochemical nanodevices for energy applications. The barrier is believed to arise from space-charge regions generated by mobile ions by analogy to semiconductor junctions. Here we show that something different is at play by studying ion transport in a bicrystal of yttria (9% mol) stabilized zirconia (YSZ), an emblematic oxide ion conductor. Aberration-corrected scanning transmission electron microscopy (STEM) provides structure and composition at atomic resolution, with the sensitivity to directly reveal the oxygen ion profile. We find that Y segregates to the grain boundary at Zr sites, together with a depletion of oxygen that is confined to a small length scale of around 0.5nm. Contrary to the main thesis of the space-charge model, there exists no evidence of a long-range O vacancy depletion layer. Combining ion transport measurements across a single grain boundary by nanoscale electrochemical strain microscopy (ESM), broadband dielectric spectroscopy measurements, and density functional calculations, we show that grain-boundary-induced electronic states act as acceptors, resulting in a negatively charged core. Besides the possible effect of the modified chemical bonding, this negative charge gives rise to an additional barrier for ion transport at the grain boundary.


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We acknowledge financial support by Spanish MICINN through grants MAT2011-27470-C01 and Consolider Ingenio 2010 - CSD2009-00013 (Imagine), by CAM through grant S2009/MAT-1756 (Phama) and by the ERC starting Investigator Award, grant #239739 STEMOX. RS wishes to acknowledge the MICINN (Spain) for granting a Ramon y Cajal fellowship. MAF is Research Fellow of CONICET (Argentine). Financial support of CONICET is gratefully acknowledged. OJD acknowledges a postdoctoral fellowship from JCCM. JS acknowledges a Juan de la Cierva fellowship from MICINN (Spain). The authors thank Dr. Hugo Schlich from Mateck GmbH for providing information about the process of bicrystals production, Masashi Watanabe for the Digital Micrograph PCA plug-in and J. Luck for help with specimen preparation, and A. de Andrés for helpful discussion and assistance on experimental matters. Electron microscopy observations at ORNL (SJP, MV) were sponsored by the Materials Sciences and Engineering Division of the U.S. Department of Energy (DOE) and and through the Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientific User Facilities Division, DOE-BES. ESM measurements (SVK, SJ, AK) were performed at the Center for Nanophase Materials Sciences and supported by the Division of Scientific User Facilities of the U.S. Department of Energy (DOE).

Uncontrolled Keywords:Yttria-stabilized zirconia, Tilt grain-boundaries, Space-charge, Thin-films, Conductivity, Energy, Oxide, Electrolytes, Conductors, Nanoscale.
Subjects:Sciences > Physics > Electricity
Sciences > Physics > Electronics
ID Code:35279
Deposited On:02 Feb 2016 10:59
Last Modified:10 Dec 2018 14:57

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