title: Paving the way to nanoionics: atomic origin of barriers for ionic transport through interfaces.
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 0.5 nm. 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.
authors.affiliation: GFMC, Departamento de Física Aplicada III, Facultad de Física, Universidad Complutense de Madrid, Campus Moncloa, 28040 Madrid, Spain.|Departamento de Química-INQUISUR,Universidad Nacional del Sur, Av. Alem 1253, Av. Alem 1253,, 8000 Bahía Blanca, Argentina.
authors.forename: M A
authors.initials: MA
authors.lastname: Frechero
authors.affiliation: GFMC, Departamento de Física Aplicada III, Facultad de Física, Universidad Complutense de Madrid, Campus Moncloa, 28040 Madrid, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Rocci
authors.affiliation: GFMC, Departamento de Física Aplicada III, Facultad de Física, Universidad Complutense de Madrid, Campus Moncloa, 28040 Madrid, Spain.|Materials Science &Technology Division, Oak Ridge, TN 37831, USA.
authors.forename: G
authors.initials: G
authors.lastname: Sánchez-Santolino
authors.affiliation: Center for Nanophase Materials Sciences, Oak Ridge, TN 37831, USA.
authors.forename: Amit
authors.initials: A
authors.lastname: Kumar
authors.affiliation: GFMC, Departamento de Física Aplicada III, Facultad de Física, Universidad Complutense de Madrid, Campus Moncloa, 28040 Madrid, Spain.|Materials Science &Technology Division, Oak Ridge, TN 37831, USA.
authors.forename: J
authors.initials: J
authors.lastname: Salafranca
authors.affiliation: GFMC, Departamento de Física Aplicada III, Facultad de Física, Universidad Complutense de Madrid, Campus Moncloa, 28040 Madrid, Spain.
authors.forename: Rainer
authors.initials: R
authors.lastname: Schmidt
authors.affiliation: GFMC, Departamento de Física Aplicada III, Facultad de Física, Universidad Complutense de Madrid, Campus Moncloa, 28040 Madrid, Spain.
authors.forename: M R
authors.initials: MR
authors.lastname: Díaz-Guillén
authors.affiliation: GFMC, Departamento de Física Aplicada III, Facultad de Física, Universidad Complutense de Madrid, Campus Moncloa, 28040 Madrid, Spain.
authors.forename: O J
authors.initials: OJ
authors.lastname: Durá
authors.affiliation: GFMC, Departamento de Física Aplicada III, Facultad de Física, Universidad Complutense de Madrid, Campus Moncloa, 28040 Madrid, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Rivera-Calzada
authors.affiliation: Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA.|Materials Science &Technology Division, Oak Ridge, TN 37831, USA.
authors.forename: R
authors.initials: R
authors.lastname: Mishra
authors.affiliation: Center for Nanophase Materials Sciences, Oak Ridge, TN 37831, USA.
authors.forename: Stephen
authors.initials: S
authors.lastname: Jesse
authors.affiliation: Materials Science &Technology Division, Oak Ridge, TN 37831, USA.|Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA.
authors.forename: S T
authors.initials: ST
authors.lastname: Pantelides
authors.affiliation: Center for Nanophase Materials Sciences, Oak Ridge, TN 37831, USA.
authors.forename: Sergei V
authors.initials: SV
authors.lastname: Kalinin
authors.affiliation: Materials Science &Technology Division, Oak Ridge, TN 37831, USA.|GFMC, Departamento de Física Aplicada III, Facultad de Física, Universidad Complutense de Madrid, Campus Moncloa, 28040 Madrid, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Varela
authors.affiliation: Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Pennycook
authors.affiliation: GFMC, Departamento de Física Aplicada III, Facultad de Física, Universidad Complutense de Madrid, Campus Moncloa, 28040 Madrid, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Santamaria
authors.affiliation: GFMC, Departamento de Física Aplicada III, Facultad de Física, Universidad Complutense de Madrid, Campus Moncloa, 28040 Madrid, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Leon