Large zinc cation occupancy of octahedral sites in mechanically activated zinc ferrite powders

Abstract

The cation site occupancy of a mechanically activated nanocrystalline zinc ferrite powder was determined as (Zn0.552+Fe0.183+)tet[Zr0.452+Fe1.823+]octO4 through analysis of extended x-ray absorption fine structure measurements, showing a large redistribution of cations between sites compared to normal zinc ferrite samples. The overpopulation of cations in the octahedral sites was attributed to the ascendance in importance of the ionic radii over the crystal energy and bonding coordination in determining which interstitial sites are occupied in this structurally disordered powder. Slight changes are observed in the local atomic environment about the zinc cations, but not the iron cations, with respect to the spinel structure. The presence of Fe3+ on both sites is consistent with the measured room temperature magnetic properties.

Cationic exchange in nanosizedZnFe2O4spinel revealed by experimental and simulated near-edge absorption structure

“…Fourier transform (FT) of χ(k) at Zn and Fe K-edges without phase correction are shown in Fig. 2 and fit results are summarized in Tables I and II, respectively. Similarly to previous works [9,10,11], there is a reduction of the amplitude of the main peaks when compared to bulk ZnFe 2 O 4 , associated with the local structural disorder at particle surface layer. Ideally, in normal ZnFe 2 O 4 the zinc atoms are tetra-coordinated by oxygens at 1.996Å and 12 Fe atoms are at 3.500Å as second neighbors.…”

“…Conversely, there is still some lack of clarity concerning Zn non-equilibrium positions and its effects. Some results indicates that Zn non-equilibrium location produces an overpopulation of B-sites by both Zn and Fe ions [10], while other claims that it distorts the spinel structure and brings about an amorphous state [9]. Thus, more * Electronic address: stewart@fisica.unlp.edu.ar studies are needed concerning the less-explored Zn local geometry to completely understand the origin of the nonequilibrium cation distribution in nanosized ZnFe 2 O 4 .…”

“…Iron (III) occupancy of both A and B-sites in nanocrystalline ZnFe 2 O 4 has been extensively proved by Mössbauer spectroscopy [1,2,6,7,8], nuclear magnetic resonance [5], neutron diffraction [3], x-ray absorption [9,10,11,12], and indirectly throughout magnetic measurements [2,3,4,13,14]. To a much lesser extend, Extended X-ray Absorption Fine Structure (EXAFS) studies at Zn K-edge suggest that Zn ions are transferred from its equilibrium position (sites A) to B-sites when the particle size decreases [9,10,11]. Conversely, there is still some lack of clarity concerning Zn non-equilibrium positions and its effects.…”

Effect of Preparation on Structure and Magnetic Properties of ZnFe2O4

“…Recently, ZnFe 2 O 4 nanoparticles prepared by various methods, such as traditional ceramic synthesis, aerogel procedure, low-temperature hydroxide co-precipitation and hydrothermal synthesis, have been studied and observed to be ferrimagnetic or superparamagnetic. The origin of the ferrimagnetic properties of ZnFe 2 O 4 and other spinel ferrite nanoparticles was studied using lowtemperature Mössbauer spectrometry with applied magnetic field parallel to the direction of gamma rays [4][5][6][7][8][9]. Large inversion parameters were obtained when the particle size is decreased, and there are spin cantings in both A and B sites.…”

Role of mode of heating on the synthesis of nanocrystalline zinc ferrite

“…ions are distributed over the A-and B-sites. This cationic rearrangement leads to the formation of two magnetic sublattices, which are responsible for the enhanced magnetization when compared with normal ZnFe 2 O 4 (Sepelak et al 1997;Oliver et al 2000;Jeyadevan et al 1994).…”