Phase composition and crystal structure determination of cobalt ferrite, modified with Ce, Nd and Dy ions by X-ray and neutron diffraction

Abstract

In order to study the possibilities for the incorporation of lanthanide ions in the spinel crystal lattice, cobalt ferrite CoFe2O4 modified by the lanthanide ions Ce(III), Nd(III), аnd Dy(III) was prepared using the sol-gel method, and two diffraction techniques, XRD and neutron diffraction, were applied to detect the position of the lanthanide ions. The samples were characterized by several techniques after preparation to confirm the formation of the spinel structure. The crystallization of the samples from the precursor powder was followed by TG/DTA so that the optimal calcination temperature could be determined. The phase homogeneity of the samples calcined at 550 °C was proved by XRD diffraction and Mossbauer spectroscopy. The data from Raman spectroscopy confirmed the spinel structure of the samples with the characteristic bands for spinel structure showing metal ions in octahedral and tetrahedral sublattice. Based on XRD, it was found that the size of the crystallites was influenced by the atomic number Z of the modifying Ln ions (58Ce, 60Nd, 66Dy) and their content; the increase of the Z caused an increase of the crystallite size, while the increase of the content caused a decrease of the crystallite size. The increase of the calcining temperature from 350 to 750 °C caused an increase of the cell parameter as a result of lattice expansion. The data for the crystal structure from XRD and neutron diffraction were compared; the cation distribution and thereby the inversion degree i was determined, presented as (A1-iBi)[AiB2-i]O4 by both diffraction methods. Based on the data from XRD and neutron diffraction it was concluded that the larger lanthanide ions do not replace the Fe3+ ions in the spinel structure.