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DOE OSTI · 1787981

Probing the meta-stability of oxide core/shell nanoparticle systems at atomic resolution

Roldan, Manuel A.·Mayence, Arnaud·López-Ortega, Alberto·Ishikawa, Ryo·Salafranca, Juan·Estrader, Marta·Salazar-Alvarez, German·Dolors Baró, M.·Nogués, Josep·Pennycook, Stephen J.·Varela, Maria
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Abstract

Hybrid nanoparticles allow exploiting the interplay of confinement, proximity between different materials and interfacial effects. However, to harness their properties an in-depth understanding of their (meta)stability and interfacial characteristics is crucial. This is especially the case of nanosystems based on functional oxides working under reducing conditions, which may severely impact their properties. Here, the in-situ electron-induced selective reduction of Mn 3 O 4 to MnO is studied in magnetic Fe 3 O 4 /Mn 3 O 4 and Mn 3 O 4 /Fe 3 O 4 core/shell nanoparticles by means of high-resolution scanning transmission electron microscopy combined with electron energy-loss spectroscopy. Such in-situ transformation allows mimicking the actual processes in operando environments. A multi-stage image analysis using geometric phase analysis combined with particle image velocity enables direct monitoring of the relationship between structure, chemical composition and strain relaxation during the Mn 3 O 4 reduction. In the case of Fe 3 O 4 /Mn 3 O 4 core/shell the transformation occurs smoothly without the formation of defects. However, for the inverse Mn 3 O 4 /Fe 3 O 4 core/shell configuration the electron beam-induced transformation occurs in different stages that include redox reactions and void formation followed by strain field relaxation via formation of defects. This study highlights the relevance of understanding the local dynamics responsible for changes in the particle composition in order to control stability and, ultimately, macroscopic functionality.

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRYcore-shell nanoparticlesin-situ transformationsmagnetic oxidesscanning transmission electron microscopy

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Roldan, Manuel A., Mayence, Arnaud, López-Ortega, Alberto, Ishikawa, Ryo, Salafranca, Juan, Estrader, Marta, Salazar-Alvarez, German, Dolors Baró, M., Nogués, Josep, Pennycook, Stephen J., Varela, Maria. 2020-09-01. Probing the meta-stability of oxide core/shell nanoparticle systems at atomic resolution. https://doi.org/10.1016/j.cej.2020.126820

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