Bimodal grain growth in ceramics

In general, microstructure evolution is believed to be a thermally activated process due to its dependence on mass transport by diffusion. However, in functional ceramics as the perovskite SrTiO3 and related materials, non-Arrhenius behavior occurs during microstructure evolution: at higher temperatures, finer microstructures can occur. This unexpected behavior is associated with bimodal microstructures and segregation. Its complete understanding allows tailoring microstructures according to a given need. Controlling the grain growth rate allows well-controlled unimodal fine-grained or coarse microstructures. Even quasi-single crystalline microstructures can be obtained with grains of a size of 100ds of µm, if segregation and space charge are carefully engineered. This high degree of microstructure control offers immense potential to tailor properties: both ionic and electronic conductivities of grain boundaries are of central importance e.g. for proton conductors (BaZrO3), Li conductors (LixLayTiO3) and oxygen conductors (CeO2) and many other applications.
To obtain full microstructural control, a careful analysis of bimodal microstructure evolution is needed. This can only be achieved by establishing a digital twin, e.g. using a phase field model for bimodal microstructure evolution. The obtained numbers allow investigating nucleation behavior of bimodal microstructures.

References
W. Rheinheimer, E. Schoof, M. Selzer, B. Nestler & M. J. Hoffmann: „Non-Arrhenius grain growth in strontium titanate: Quantification of bimodal grain growth“, Acta Materialia, 2019
W. Rheinheimer & M. J. Hoffmann: ‘Grain growth in perovskites: What is the impact of boundary transitions?’, Current Opinion in Solid State and Materials Science, 2016
W. Rheinheimer & M. J. Hoffmann: ‘Non-Arrhenius behavior of grain growth in strontium titanate: New evidence for a structural transition of grain boundaries’, Scripta Materialia, 2015
W. Rheinheimer, M. Bäurer & M. J. Hoffmann: ‘A reversible wetting transition in strontium titanate and its influence on grain growth and the grain boundary mobility’, Acta Materialia, 2015