Understanding ion transport across grain boundaries.

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

Barcelona

Encuentro; 7th. International Discussion Meeting on Relaxation in Complex Systems; 2013

Universitat Politècnica de Catalunya

Understanding ion transport in ionically conducting materials is nowadays of primary importance in order to optimize their use as electrolytes in solid state batteries and fuel cells. Since solid electrolytes are usually in polycrystalline form, it is blocking of ions at grain boundaries that eventually limits ion transport through the material. However, the microscopic origin of the barrier for ion transport across grain boundaries is not well established yet. Here we present a study of structure, composition, and ion transport across a single grain boundary in a bicrystal of the oxide ion conductor 9 mol % yttria stabilized zirconia (YSZ) by combining STEM-EELS aberration corrected microscopy, nanoscale electrochemical strain microscopy (ESM), and broadband dielectric spectroscopy measurements. We obtain relevant microscopic parameters that determine ion transport properties at the nanoscale such as the built-in potential at the interfacial plane, the space charge layer thickness, and the Debye screening length. The values obtained for these magnitudes are much lower than previous estimates from measurements on ceramic samples that present a complex distribution of multiple grain boundaries. In fact, we find a remarkable agreement with the predictions of simple theoretical space charge models, thus solving doubts cast recently on their predictive value to describe ion transport across grain boundaries.