Nanostructured spinel cobalt ferrites: Fe and Co chemical state, cation distribution and size effects by X-ray photoelectron spectroscopy

Marzia Fantauzzi; Fausto Secci; Marco Sanna Angotzi; Cristiana Passiu; Carla Cannas; Antonella Rossi

doi:10.1039/c9ra03488a

Nanostructured spinel cobalt ferrites: Fe and Co chemical state, cation distribution and size effects by X-ray photoelectron spectroscopy

RSC Adv. 2019 Jun 18;9(33):19171-19179. doi: 10.1039/c9ra03488a. eCollection 2019 Jun 14.

Authors

Marzia Fantauzzi¹, Fausto Secci^{1

2}, Marco Sanna Angotzi^{1

3}, Cristiana Passiu², Carla Cannas^{1

3}, Antonella Rossi^{1

3}

Affiliations

¹ Dipartimento di Scienze Chimiche e Geologiche, Università degli Studi di Cagliari, Campus di Monserrato S.S. 554 Italy fantauzzi@unica.it.
² Department of Materials, ETH Zürich Vladimir-Prelog-Weg 5 Zurich Switzerland.
³ INSTM, UdR Cagliari Italy.

Abstract

Nanostructured spinel cobalt ferrite samples having crystallite size ranging between 5.6 and 14.1 nm were characterized by X-ray photoelectron spectroscopy and X-ray induced Auger electron spectroscopy in order to determine the chemical state of the elements, the iron/cobalt ratio and the cation distribution within tetrahedral and octahedral sites. The presence of size-dependent trends in the binding energy of the main photoelectron peaks and in the kinetic energy of the X-ray induced O KLL signal was also investigated. The results showed that iron is present as Fe^III and cobalt is present as Co^II. The iron/cobalt ratio determined by XPS ranges between 1.8 and 1.9 and it is in very good agreement, within experimental uncertainty, with the expected 2 : 1 ratio. The percentage of Fe in octahedral sites ranges between 62% and 64% for all samples. The kinetic energy of the O KLL signals increases with crystallite size. These results are explained in terms of changes in the ionicity of the metal-oxygen bonds. The results of this investigation highlight how the XPS technique represents a powerful tool to investigate the composition, the chemical state and inversion degree of cobalt spinel ferrites, contributing to the comprehension of their properties.