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

FRECHERO M. A.; ROCCI, M.; SANCHEZ-SANTOLINO, G.; KUMAR, AMIT; SALAFRANCA, JUAN; SCHMIDT,R.; DIAZ GUILLEN, M.; DURA, O.; RIVERA-CALZADA, A.; MISHRA, R.; JESSE, STEPHEN; PANTELIDES,S.; KALININ, SERGEI; VARELA, M.; PENNYCOOK, STEVE; SANTAMARIA, JACOBO; LEON,C.

Congreso; XIII TREFEMAC; 2015

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 dierent is at play by studyingion transport in a bicrystal of yttria (9% mol) stabilized zirconia (YSZ), an emblematic oxide ion conductor. Aberration-corrected scanning transmission electronmicroscopy (STEM) provides structure and composition at atomic resolution, with the sensitivity to directly reveal the oxygen ion prole. We nd that Y segregates to the grain boundary at Zr sites, together with a depletion of oxygen that is conned 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 cceptors,resulting in a negatively charged core. Ultimately, it is this negative charge which gives rise to the barrier for ion transportat the grain boundary.