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.
Highlights
The synthesis of mixeAd-bmstertaaclts:pTihnelssybnatsheedsiosnofsumbisxteitdu-tmedet a-lGsap2iOne3lissbreapseodrtoend suusbinsgtitmuteetdal -Ga2O3 is reported using meta acetylacetonate precursors in soalcveottyhlearcmetaolnraetaecptiroencsuwrsiotrhsainlcosohlovlostahsesromlvael nretascattio2n40s w Cit.hNaelwcoohxoildseass solvents at 240 C
We report a new solvothermal route to transition-metal containing gallium oxides by using acetylacetonate precursors and organic solvents. This has allowed the preparation of new examples of Mn- and Fe-containing gallium oxide spinels, and the first chromium-gallium oxide, and we investigate the oxidation state distributions and magnetism of the materials using a variety of methods
Electron paramagnetic resonance (EPR) experiments were performed on a commercial (MiniScope 400, Magnettech, Berlin, Germany) X-band (9.44 GHz) EPR spectrometer coupled to helium flux cryosystem (ESR 900, Oxford Instruments, Abingdon, UK) permitting sample temperatures to be varied between 4.2 and 350 K
Summary
For the synthesis of Cr-substituted Ga2O3, 0.3 g (0.82 mmol) of Ga(acac) (Sigma-Aldrich, 99.99%, Gillingham, UK) and 0.093 g (0.35 mmol) of CrCl3·6H2O (Sigma-Aldrich, 96%, Gillingham, UK) were added into a 23 mL PTFE-lined steel autoclave followed by of 10 ml 1,4-butanediol (Alfa Aesar, 99%, Heysham, UK). The mixture was stirred for 20 min under reflux and cooled for 30 min to effect the precipitation of dark brown crystals of Mn(acac)3 These crystals were filtered by vacuum filtration and washed several times with an acetone:water mixture (1:1 by volume). The mixture was stirred at room temperature for 10 min before being sealed in a steel autoclave and placed in a fan-assisted oven pre-heated to 240 ◦C for 24 h. The autoclave was removed from the oven and allowed to cool naturally to ambient temperature and the solid product collected by vacuum filtration. This was washed with copious amounts of acetone to yield a light brown powder. Spinel-structured materials with up to a 1:1 ratio of Fe:Ga could be produced in the reactions, and two samples were prepared for comparison, with ratios of Fe:Ga of 3:7 and 1:1
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
