In-Situ Synchrotron Light Studies of Cobalt Ferrite and Cobalt(II) Oxide Synthesis via The Polyol Method: Uncovering Intermediate Phases through In-Situ XRD and SAXS Monitoring

The synthesis of cobalt ferrite (CFO) and cobalt (II) oxide (CO) nanoparticles (NP-CFO, NP-CO) through the polyol method has garnered considerable interest due to their promising applicative potential in fields such as catalysis, electronics, biomedical engineering, and magnetic materials science. Detailed knowledge of the processes taking place during synthesis is crucial information for the precise adjustment of synthesis parameters. We have used synchrotron radiation X-ray diffraction (SR-XRD) and small-angle X-ray scattering (SR-SAXS) at the Elettra synchrotron radiation facility, to monitor in situ the formation of NP-CFO and NP-CO during polyol synthesis. The analysis of time-resolved XRD and SAXS patterns provides insight into the evolving crystallographic structure and morphological changes during synthesis.<br/>Our findings reveal curious and original insights into the evolution of the reactant during the synthesis, such as the presence of intermediates (e.g., layered hydroxide salts, LHS) and the appearance of sub-nanometre-sized precursor phases likely acting as pre-nucleation clusters of NP-CFO/CO phases. The in-situ monitoring allowed us to capture the dynamic evolution of these intermediates, providing valuable information on their formation pathways and growth kinetics, which significantly affect the nucleation and growth processes of the cobalt-based nanoparticles. The unambiguous identification of these intermediates sheds light on the intricate mechanisms governing the process and represents a crucial step towards optimising the polyol synthesis and improving the purity and crystallinity of the final products.<br/>The understanding of the synthesis dynamics and mechanistic insights gained from this in-situ study advance tailored synthesis strategies for producing high-quality NP-CFO and NP-CO materials. This also provides relevant details for better interpretation of the magnetic properties of antiferromagnetic materials such as CO, which is critical to avoid ambiguities given its relatively low magnetic signal.