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Instruments / Technical Area	Publication Details	Published
I22-Small angle scattering & Diffraction	In situ and ex situ X-ray diffraction and small-angle X-ray scattering investigations of the sol–gel synthesis of Fe3N and Fe3C Matthew S. Chambers , Robert D. Hunter , Martin J. Hollamby , Brian R. Pauw , Andrew J. Smith , Tim Snow , Ashleigh Danks , Zoe Schnepp Inorganic Chemistry DOI: 10.1021/acs.inorgchem.1c03442 Diamond Proposal Number(s): [11969] Open Access Show Abstract ▼ Abstract: Iron nitride (Fe3N) and iron carbide (Fe3C) nanoparticles can be prepared via sol–gel synthesis. While sol–gel methods are simple, it can be difficult to control the crystalline composition, i.e., to achieve a Rietveld-pure product. In a previous in situ synchrotron study of the sol–gel synthesis of Fe3N/Fe3C, we showed that the reaction proceeds as follows: Fe3O4 → FeOx → Fe3N → Fe3C. There was considerable overlap between the different phases, but we were unable to ascertain whether this was due to the experimental setup (side-on heating of a quartz capillary which could lead to thermal gradients) or whether individual particle reactions proceed at different rates. In this paper, we use in situ wide- and small-angle X-ray scattering (wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS)) to demonstrate that the overlapping phases are indeed due to variable reaction rates. While the initial oxide nanoparticles have a small range of diameters, the size range expands considerably and very rapidly during the oxide–nitride transition. This has implications for the isolation of Rietveld-pure Fe3N, and in an extensive laboratory study, we were indeed unable to isolate phase-pure Fe3N. However, we made the surprising discovery that Rietveld-pure Fe3C nanoparticles can be produced at 500 °C with a sufficient furnace dwell time. This is considerably lower than the previous reports of the sol–gel synthesis of Fe3C nanoparticles.	Apr 2022
I15-1-X-ray Pair Distribution Function (XPDF)	Evolution of the local structure in the sol–gel synthesis of Fe3C nanostructures Matthew S. Chambers , Dean S. Keeble , Dean Fletcher , Joseph A. Hriljac , Zoe Schnepp Inorganic Chemistry 52 DOI: 10.1021/acs.inorgchem.0c03692 Diamond Proposal Number(s): [15959] Open Access Show Abstract ▼ Abstract: The sol–gel synthesis of iron carbide (Fe3C) nanoparticles proceeds through multiple intermediate crystalline phases, including iron oxide (FeOx) and iron nitride (Fe3N). The control of particle size is challenging, and most methods produce polydisperse Fe3C nanoparticles of 20–100 nm in diameter. Given the wide range of applications of Fe3C nanoparticles, it is essential that we understand the evolution of the system during the synthesis. Here, we report an in situ synchrotron total scattering study of the formation of Fe3C from gelatin and iron nitrate sol–gel precursors. A pair distribution function analysis reveals a dramatic increase in local ordering between 300 and 350 °C, indicating rapid nucleation and growth of iron oxide nanoparticles. The oxide intermediate remains stable until the emergence of Fe3N at 600 °C. Structural refinement of the high-temperature data revealed local distortion of the NFe6 octahedra, resulting in a change in the twist angle suggestive of a carbonitride intermediate. This work demonstrates the importance of intermediate phases in controlling the particle size of a sol–gel product. It is also, to the best of our knowledge, the first example of in situ total scattering analysis of a sol–gel system.	May 2021
I11-High Resolution Powder Diffraction	In situ synchrotron X-ray diffraction study of the sol-gel synthesis of Fe3N and Fe3C Zoe Schnepp , Ashleigh Danks , Martin Hollamby , Brian Pauw , Claire Murray , Chiu Tang Chemistry Of Materials 27 (14), 5094–5099 DOI: 10.1021/acs.chemmater.5b01811 Diamond Proposal Number(s): [9566] Show Abstract ▼ Abstract: Sol-gel chemistry is a powerful tool for the synthesis of porous or nanocrystalline structures of a wide range of materials. The morphology and composition of the final product can depend strongly on the mechanism that operates during the heating step, as has been demonstrated in many investigations of binary, ternary and quaternary metal oxides. We demonstrate the complex phase transformations occurring in a transition metal carbide (Fe3C, cementite) synthesis using in situ synchrotron X-ray diffraction. Our new study proves the existence of multiple intermediate phases and elucidates how oxide-nitride and nitride-carbide phase transformations can occur. This is particularly important as many transition metal nitrides and carbides are metastable, which renders their stability windows sensitive to small changes in sol-gel methodology	Jul 2015

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