This work explores the benefits of single-phase oxalate precursors for the preparation of spinel ferrites by thermal decomposition. A direct comparison between the genuine oxalate solid solution and the physical mixture of simple oxalates is presented using the case study of cobalt ferrite preparation. The mixing of metal cations within a single oxalate structure could be verified prior to its thermal decomposition by several non-destructive experimental techniques, namely Mössbauer spectroscopy, X-ray powder diffraction (XRD) and energy-dispersive X-ray spectroscopy. In situ XRD experiments were conducted to compare the decomposition processes of the solid solution and the physical mixture. Additionally, the decomposition products of the FeCo oxalate solid solution were studied ex situ by means of N 2 adsorption, Mössbauer spectroscopy and XRD. The results obtained for different reaction temperatures demonstrate the possibilities to easily control the physical properties of the prepared oxides.
This work focuses on the preparation of bimetal Fe−Cu oxalates by a co‐precipitation reaction in an aqueous solution and subsequently on their thermally induced decomposition. The formation of solid solutions of Fe−Cu oxalates with various Fe/Cu ratios was studied by energy dispersive X‐ray analysis, X‐ray powder diffraction, transmission 57Fe Mössbauer spectroscopy, and scanning electron microscopy. The results suggest that the bimetal Fe−Cu oxalate precipitated in a structure similar to β‐FeC2O4 ⋅ 2H2O. The maximum relative amount of Cu obtained within the bimetal oxalate was approximately 40 %. However, the single bimetal phase composition was obtained only for a limited range of Fe/Cu ratios. The Fe‐rich samples contained also β‐FeC2O4 ⋅ 2H2O, while the Cu‐rich samples were predominantly composed of CuC2O4 ⋅ nH2O and contained much lower amounts of Fe than expected. The thermal decomposition of the prepared oxalate with the nominal Fe/Cu ratio of 65/35 was studied by in‐situ X‐ray powder diffraction in combination with ex‐situ Mössbauer spectroscopy. The mixing of both metals at the molecular level allowed the preparation of copper ferrite particles at a relatively low temperature of 470 °C.
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