Cation distribution of ZnxCo1-xFe2O4 nanoparticles: a resonant X-ray diffraction study

Abstract

In this study, it was successfully explored the use of resonant X-ray diffraction, with energies tuned to the absorption edges of Zn2þ, Fe3þ and Co2þ, as an innovative approach to obtain the structural properties of the as-synthesized ZnxCo1-xFe2O4 nanoparticles (NPs) (0.0 x 1.0). Zinc-cobalt ferrite, which has potential application in magnetic recording, photo-magnetic devices, biomedicine, gas sensing, catalysis, etc., was synthesized by solution combustion method and analysed by X-ray diffraction, Raman and Mossbauer spectroscopies. Rietveld re € finement shows that all samples present single-phase cubic spinel structure (space group Fd3m) with lattice parameter increasing linearly with the Zn-content (x), from 8.37 Å to 8.43 Å. The data also showed that the average diameter of the crystallites sets around 45 nm and do not depend on the Zn-content. In addition, a complete cationic distribution between A- and Bsublatices was obtained by resonant X-ray diffraction and compared with the partial cationic distribution obtained by Raman and Mossbauer spectroscopies. A strong correlation between the data was found. € Despite evidences of the presence of Fe3þ-ions in both crystallographic sites, it was found that as the Zncontent increases, Zn2þ-ions tend to preferentially occupy A-sites, forcing Fe3þ-ions to occupy B-sites. As results, it was observed that with increasing Zn-content, the average distance between cations and anions increases in A-sites (from 1.88 Å to 1.98 Å) and decreases in B-sites (from 2.06 Å to 2.03 Å). Resonant X-ray diffraction and Mossbauer data indicate that the replacement of Co € 2þ- by Zn2þ-ions changes substantially the NPs’ hyperfine parameters, suggesting that the NPs with intermediate Zncontent present lower crystalline quality while compared to the samples with x ¼ 0.0 and x ¼ 1.0. Evidence of symmetry reduction (from m3m to 3m) in the B-sites was obtained, which is in accordance with the variation verified in the integrated areas and energies found for the Raman modes below 600 cm1 . Finally, the excellent agreement between the results obtained by resonant X-ray diffraction, Raman spectroscopy and Mossbauer spectroscopy indicate the robustness of the approach herein used to € assess the cation distribution in quaternary spinel ferrites.