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 Zn2+, Fe3+ and Co2+, 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 refinement shows that all samples present single-phase cubic spinel structure (space group F d 3 ¯ m ) with lattice parameter increasing linearly with the Zn-content (x), from 8.37 A to 8.43 A. 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 B-sublatices 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 Fe3+-ions in both crystallographic sites, it was found that as the Zn-content increases, Zn2+-ions tend to preferentially occupy A-sites, forcing Fe3+-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 A to 1.98 A) and decreases in B-sites (from 2.06 A to 2.03 A). Resonant X-ray diffraction and Mossbauer data indicate that the replacement of Co2+- by Zn2+-ions changes substantially the NPs’ hyperfine parameters, suggesting that the NPs with intermediate Zn-content present lower crystalline quality while compared to the samples with x = 0.0 and x = 1.0. Evidence of symmetry reduction (from m 3 ¯ m to 3 ¯ m ) 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 cm−1. 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.