Local Structural Studies Through EXAFS and Effect of Fe²⁺or Fe³⁺ Existence in ZnO Nanoparticles

Abstract

A simple solution-based chemical precipitation method was used to synthesize the Fe-doped ZnO nanoparticles. X-ray Photoelectron Spectroscopy (XPS) measurement showed that mostly Fe2+ ions are incorporated in a lower percentage of Fe doping, while a higher percentage leads to Fe3+. The broad absorption band in the visible range shows the d–d crystal field transitions between the multiplets of 3d5 configuration of the high spin Fe3+ substituting Zn2+ under the influence of a tetrahedral ZnO crystal field. Raman measurement also supports the optical absorption data. ESR results show that the occurrence of broad signals is due to the exchange interactions among the TM ions in the doped samples. Fe exists in a mixed phase in Fe1 and the wide curve in Fe10 is due to the exchange interaction among Fe3+– Fe3+. EXAFS measurements confirm that the spectral features showing the peak edge position is similar to Fe2O3 corresponding to the Fe3+ state. From this, it can be inferred that Fe exists mostly in a +3 oxidation state in all the samples, but there may be existence of +2 states in the surface layers as observed from XPS measurement. Fe1 shows RTFM with a coercivity of ∼70 Oe. The non-saturating, linear magnetic moment at higher applied magnetic field is due to the paramagnetic contribution from the uncoupled Fe3+ ions.

Growth and Structure of Single-Crystal ZnO Nanorods Codoped with Fe and Li for Multiferroic Applications

“…The fitting results are summarized in Table . The peak energy and total area are quite similar to those reported in earlier publications devoted to ZnO nanostructures doped with iron. , The integral intensity of the pre-edge 1s → 3d XANES peak (0.18) occupies an intermediate position between typical octahedral (below 0.1) and tetrahedral (above 0.25) configurations and is rather similar to rare examples of pentacoordinated ferric ions, such as yoderite, thus confirming the model derived from the Rietveld refinement.…”

“…The peak energy and total area are quite similar to those reported in earlier publications devoted to ZnO nanostructures doped with iron. 33,51 The integral intensity of the pre-edge 1s → 3d XANES peak (0.18) occupies an intermediate position between typical octahedral (below 0.1) and tetrahedral (above 0.25) configurations and is rather similar to rare examples of pentacoordinated ferric ions, such as yoderite, 50 2. The EXAFS fit is generally compatible with the crystallographic model derived from the Rietveld refinement, although it underestimates the apparent shift of the Fe 3+ ion from the nominal position of Zn 2+ in the pristine ZnO crystal structure.…”

Photoluminescence and Photocatalytic Properties of MWNTs Decorated with Fe-Doped ZnO Nanoparticles

“…The low and broad absorption in the 400–600 nm wavelength range is due to the interfacial charge transfer and d–d transition between the multiplets of the 3d 5 configuration of the high spin Fe 3+ substituting Zn 2+ under the influence of the tetrahedral ZnO crystal field. The observed transitions were assigned to the 6 A 1g ground state to 4 T 1 , 4 T 2 , 4 E and 4 A 1 excited states [ 37 , 38 ].…”

Hydro-ionothermally Generated Paramagnetic Fe State-Embedded Ferromagnetic Iron Oxide with a 2D Hexagonal Nanostructure: A Conceptual Intervention on the Methylene Blue Degradation Mechanism

“…Mathematically, M FM can be expressed as M 0 L (x) and M PM can be expressed as χ m H , where M 0 is the total spontaneous magnetic moment of the system given by Nm s , where m s is the actual spontaneous magnetic moment of each electron spin, and N is the number of spins per unit volume. L ( x ) is the Langevin function expressed as [coth­( x ) – (1/ x )], with x = Hm eff / K B T , m eff is the effective spontaneous magnetic moment of each electron spin, χ m is the PM susceptibility, and H is the applied magnetic field …”

“…L(x) is the Langevin function expressed as [coth(x) − (1/x)], with x = Hm eff /K B T, m eff is the effective spontaneous magnetic moment of each electron spin, χ m is the PM susceptibility, and H is the applied magnetic field. 54 The M−H curve fitted with the above equation is presented in the below figure, and the equation was fitted in the first quadrant by taking M 0 , m eff , and χ m as the variable parameters (Table 4). Moreover, M FM and M PM were also individually fitted after getting the desired value from the fitting.…”