KSN Vikrant, W Rheinheimer, H Sternlicht, M Bäurer, RE García “Electrochemically-driven abnormal grain growth in ionic ceramics.” Acta Materialia 200: 720-734, 2020.  https://doi.org/10.1016/j.actamat.2020.08.027

Abstract

A combined theoretical and experimental analysis was performed to understand the effects of extrinsic ionic species and point defects on the microstructural evolution of ionic polycrystalline ceramics. The model naturally incorporates the effects of drag on grain boundary motion as imposed by the interfacially accumulated charged defects for Fe doped SrTiO₃. Two moving grain boundary types, i.e., highly mobile and immobile interfaces result in abnormal grain growth. Fast moving grain boundaries leave a residual charge network behind in the interior of the grains in the form of bands of  [Fe’_Ti] which in turn electrostatically attract oxygen vacancies, thus enhancing the local ionic conductivity of the polycrystal. Three grain size populations are statistically identified: (a) a normal grain population, as one would expect would happen in classical systems; (b) an abnormal, large grain population, which corresponds to those grains whose spatial extent is statistically greater than the average; and (c) an electrochemically persistent small grain size population that is stabilized by the grain boundary electrical energy. The study herein sets the stage to assess the effects of externally applied fields such as temperature, electromagnetic fields, stresses, and chemical stimuli to develop textured, oriented microstructures as tailored for a wide range of applications.