%0 Journal Article
%A Frechero, M. A.
%A Rocci, Mirko
%A Sánchez Santolino, Gabriel
%A Salafranca, Juan
%A Schmidt, Rainer
%A Díaz Guillén, M. R.
%A Durá, O. J.
%A Rivera Calzada, Alberto Carlos
%A Varela Del Arco, María
%A Santamaría Sánchez-Barriga, Jacobo
%A León Yebra, Carlos
%T Paving the way to nanoionics: atomic origin of barriers for ionic transport through interfaces
%D 2015
%@ 2045-2322
%U https://hdl.handle.net/20.500.14352/24312
%X 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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