Investigating the preferential sites of Co2+ substitution in SrCoxFe12−xO19 using Mössbauer spectroscopy

Abstract

In this paper, a series of M-type hexagonal SrCo_xFe${}_{12-x}$O${}_{19}$ ($x=0$, 0.25, 0.5) samples have been prepared by sol–gel method. X-ray diffraction (XRD) showed that the samples produced were all p63/mmc space groups of single hexagonal crystals, and the lattice parameters a, b and c did not show the expected trend with increasing x. This was related to the valence changes and lattice distortion caused by the substitution of Co${}^{2+}$ at the 2a and 4f₂ sites. Room temperature Mössbauer spectra studies showed that when $x=0$, Fe${}^{3+}$ ions were not uniformly distributed, preferring the 4f₁, 4f₂ and 2a sites; when $x=0.25$, Co${}^{2+}$ ions preferentially displaced the 2a and 4f₂ sites and the presence of Fe${}^{2+}$ was detected; when $x=0.5$, Co${}^{2+}$ ions preferentially displaced the 4f₁ and 2b sites and the percentage of Fe${}^{2+}$ occupancy was reduced, with a greater occupancy ($R_A)$ occurring at the 12k site, indicating a preference of Fe${}^{3+}$ of the doped sample for this site. This work will provide an important reference for the variation of properties induced by different ion doping substitutions of the Fe sites in the hexagonal ferrite family.