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Nanocrystalline transition-metal gallium oxide spinels from acetylacetonate precursors via solvothermal synthesis

DOI: 10.3390/ma12050838 DOI Help

Authors: Daniel S. Cook (University of Warwick) , Reza Kashtiban (University of Warwick) , Klaus Krambrock (Universidade Federal de Minas Gerais) , Geraldo De Lima (Universidade Federal de Minas Gerais) , Humberto Stumpf (Universidade Federal de Minas Gerais) , Luciano R. S. Lara (Universidade Federal de Minas Gerais) , José Ardisson (Centro de Desenvolvimento em Tecnologia Nuclear, CDTN/CNEN) , Richard Walton (University of Warwick)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Materials , VOL 12

State: Published (Approved)
Published: March 2019
Diamond Proposal Number(s): 13841

Open Access Open Access

Abstract: The synthesis of mixed-metal spinels based on substituted γ-Ga2O3 is reported using metal acetylacetonate precursors in solvothermal reactions with alcohols as solvents at 240 °C. New oxides of Cr, Mn and Fe have been produced, all of which are formed as nanocrystalline powders, as seen by high-resolution transmission electron microscopy (HR-TEM). The first chromium-gallium mixed oxide is thus formed, with composition 0.33Ga1.87Cr0.8O4 ( = vacant site). X-ray absorption near-edge spectroscopy (XANES) at the chromium K-edge shows the presence of solely octahedral Cr3+, which in turn implies a mixture of tetrahedral and octahedral Ga3+, and the material is stable on annealing to at least 850 °C. An analogous manganese material with average chemical composition close to MnGa2O4 is shown to contain octahedral Mn2+, along with some Mn3+, but a different inversion factor to materials reported by conventional solid-state synthesis in the literature, which are known to have a significant proportion of tetrahedral Mn2+. In the case of iron, higher amounts of the transition metal can be included to give an Fe:Ga ratio of 1:1. Elemental mapping using energy dispersive X-ray spectroscopy on the TEM, however, reveals inhomogeneity in the distribution of the two metals. This is consistent with variable temperature 57Fe Mössbauer spectroscopy that shows the presence of Fe2+ and Fe3+ in more than one phase in the sample. Variable temperature magnetisation and electron paramagnetic resonance (EPR) indicate the presence of superparamagnetism at room temperature in the iron-gallium oxides.

Journal Keywords: ferrite; crystallisation; magnetism; XANES; Mössbauer spectroscopy; EPR

Subject Areas: Materials, Chemistry


Instruments: B18-Core EXAFS

Documents:
materials-12-00838-v2 (1).pdf

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