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Materials Science at Oregon State University

Understanding Crystallization Pathways Leading to Manganese Oxide Polymorph Formation

Date: Thursday, May 31st
Presenter: Dr. Bor-Rong Chen, Stanford Linear Accelerator National Laboratory


Hydrothermal synthesis is challenging in metal oxide systems with diverse polymorphism, as reaction products are often sensitive to subtle variations in synthesis parameters. This sensitivity is rooted in the non-equilibrium nature of low-temperature crystallization, where competition between different metastable phases can lead to complex multistage crystallization pathways. Here, we propose a theoretical framework to predict how particle size and solution composition influence polymorph stability during nucleation and growth. To validate this framework, we use the hydrothermal synthesis of MnO2 as a demonstration case. We investigate the nature of synthesis pathways by using in-situ X-ray techniques to monitor how the species in the solution evolves during the reaction. In the experiment, three synthesis pathways with varying potassium ion concentrations ([K+] = 0, 0.2, and 0.33 M) in the solution were studied. We find that our computed size-dependent phase diagrams qualitatively capture which metastable polymorphs appear, the order of their appearance, and their relative lifetimes, under these three [K+] conditions. This combination of computational and experimental approach offers a more rational and systematic paradigm for the aqueous synthesis of target metal oxides.

Bor-Rong Chen is a postdoctoral researcher at the SLAC National Accelerator Laboratory. Bor-Rong has been studying materials science since 2005, and she graduated with a Ph.D. in materials science and engineering from Northwestern University in 2017. As a member of the Center for Next Generation of Materials Design (CNGMD), an Energy Frontier Research Center (EFRC), Bor-Rong’s major goal is to understand the nature of reaction pathways of materials synthesis and to design more effective approach for reaching metastable phases as well as making brand new materials. Her current research involves monitoring the formation and evolution of oxides during water-based chemical reactions in real time by using in-situ X-ray analysis techniques at synchrotron radiation facilities.