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Related Experiment Video

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Atomically Defined Templates for Epitaxial Growth of Complex Oxide Thin Films

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Published on: December 4, 2014

Evolution of Atomic-Level Structure in Sub-10 Nanometer Iron Oxide Nanocrystals: Influence on Cation Occupancy and

Susan R Cooper¹, Randall O Candler¹, Alexia G Cosby¹

¹Department of Chemistry and Biochemistry and Materials Science Institute, University of Oregon, Eugene, Oregon 97403-1253, United States.

|April 29, 2020

Summary

Spinel iron oxide nanocrystals (NCs) show size-dependent structural changes, with smaller NCs exhibiting higher iron oxidation states and more vacancies. These nanoscale structural features influence NC growth dynamics.

Keywords:

nanocrystals pair distribution function analysis size-dependent spinel iron oxide total X-ray scattering

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Area of Science:

Materials Science
Nanotechnology
Solid State Chemistry

Background:

Spinel iron oxide nanocrystals (NCs) exhibit distinct core and surface structures compared to bulk materials.
Advances in synthesis allow for subnanometer size control of NCs below 10 nm, enabling investigation of size-dependent properties.

Purpose of the Study:

To study the evolution of size-dependent structure in spinel iron oxide NCs.
To determine how nanoscale structure influences NC growth.

Main Methods:

Synthesis of spinel iron oxide NCs using a continuous growth method with layer-by-layer size control (16 sizes, 3-10 nm).
X-ray total scattering data collection and pair distribution function (PDF) analysis to refine structural features like cation occupancies.

Main Results:

Average iron oxidation state increases as NC core diameter decreases from 8 to 3 nm, attributed to surface oxidation.
Oxidation stabilizes when a ~1.3 nm shell converts to maghemite.
Tetrahedrally coordinated cation vacancies increase with decreasing NC size.

Conclusions:

Smaller spinel iron oxide NCs have higher iron oxidation states and increased cation vacancies.
Reactive vacancies correlate with faster growth in NCs smaller than 8 nm, suggesting their role in growth dynamics.