A facile gel-combustion route for fine particle synthesis of spinel ferrichromite: X-ray and Mössbauer study on effect of Mg and Ni content

doi:10.1016/j.materresbull.2013.10.035

Materials Research Bulletin

Volume 50, February 2014, Pages 172-177

https://doi.org/10.1016/j.materresbull.2013.10.035 Get rights and content

Highlights

•
A novel and facile synthesis route.
•
Transformation of system from random to inverse spinel.
•
Appearance of superparamagnetism phase.

Abstract

A novel nitrate–citrate gel combustion route was used to prepare fine particle of a series Mg_1−xNi_xFeCrO₄ (0.0 ≤ x ≤ 1.0) and its structural properties were investigated. The in situ oxidizing environment provided by the nitrate ions in the gel increases the rate of oxidation and lowers the decomposition temperature of component. All the samples after sintering were characterized at room temperature by X-ray diffraction (XRD) method and Mössbauer spectroscopy techniques. The X-ray and Mössbauer studies confirmed the single phase cubic spinel structure with all Fe ions in 3+ charge state. XRD and Mössbauer studies revealed that the samples of x = 0.0, and 0.2 are random spinel and show rather broad lines, while x = 0.4–1.0 are inverse spinel.

Graphical abstract

Introduction

Ferrites are ferrimagnetic oxides; crystallize into two magnetic sub-lattices, tetrahedral (A) site and octahedral [B] site. The properties, upon which their application depends, are influenced by the cation distribution among these two sites. Ferrites are high-resistivity materials with low eddy current losses which make them potential materials for high-frequency applications such as microwave devices. The properties of ferrites have been normally found to vary on substituting the other constituent ions [1], [2]. Superparamagnetism is a unique feature of ferrites and is crucially related to many modern technologies, including ferrofluid technology, magnetic refrigeration etc. [3], [4].

Nickel-magnesium ferrite is a soft magnetic material having low magnetic coercivity and high resistivity values. The high electrical resistivity and excellent magnetic properties make this ferrite an automatic choice as a core material for power transformers in electronic and telecommunication applications in megahertz frequency regions. The wet chemical method reported on here, overcomes all drawbacks of conventional ceramic process and produce ultra-fine, homogeneous and reproducible ferrite powders using aqueous solutions of nitrate salts of constituent ions.

Mössbauer spectroscopy uses the nuclear properties to get information regarding the environment surrounding the nucleus. The very high sensitivity of the Mössbauer spectrum to the oxidation state and site occupancy of Fe³⁺ in cubic spinel makes Mössbauer spectroscopy valuable for addressing the fundamental relationships between crystal chemistry and structure. The technique can also detect the relative percentage of different charged states of the same atom like Fe²⁺ and Fe³⁺ present in the material. Being that the iron occupies two local environments, the A-site and B-site, and two species (Fe²⁺ and Fe³⁺) occupy the B-site, one might expect the spectrum to be a combination of three spectra. However, delocalization of electrons or electron hopping between Fe²⁺ and Fe³⁺ in the B- site causes the nuclei to sense an average valence in the B-site and thus the spectrum are fitted with two curves accordingly. The isomer shift of the fitted curves can be used to determine which curve corresponds to which valence ions [5], [6].

In this work, attempts to substitute magnesium by nickel were undertaken through sol–gel route. The precipitation methods always have the disadvantage that the stoichiometry of the precipitate may not be exact if one or more ions are left in solution. The sol–gel route overcomes this because the reactants never precipitate out. X-ray and Mössbauer spectral studies were carried out in order to make phase analysis. It was established that iron ions were located in two different interstitials from which oxidation state of iron was confirmed.

Section snippets

Experimental details

The A.R. grade nitrate salts (Merck Specialties Pvt. Ltd., India) of Fe, Mg, Cr and Ni were taken by the stoichiometric calculations for the synthesis of each compounds of the system Mg_1−xNi_xFeCrO₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0). As the metal nitrates are hygroscopic they were preserved in moisture free dessicator. After dissolving the metal nitrates separately in minimum de-ionized water, solutions were mixed well and a solution of citric acid was added along with a small amount of

X-ray diffraction study

XRD patterns of Mg_1−xNi_xFeCrO₄ samples sintered at 600 °C for 8 h are shown in Fig. 1 which confirms the single cubic spinel phase. The diffraction lines are found to be sharp and no other phases has been detected for all the samples. The material has a well-defined polycrystalline nature, belonging to the fcc Bravais lattice; which confirm the spinel structure [9].

The irregular variation of lattice parameter ‘a’ with Ni content can be explained on the basis of ionic radii. Both Mg (0.65 Å) and Ni

Conclusions

The system Mg_1−xNi_xFeCrO₄ is successively synthesized by the facile sol–gel auto-combustion method at controlled pH and exhibits the single phase cubic spinel structure. The variation of lattice parameter ‘a’ with Ni content is due to structural change, atomic weight and the replacement of larger radius ion Mg²⁺ by smaller radius ion Ni²⁺. The calculated site radii and bond lengths show that the octahedral site radius is larger than the tetrahedral site. The isomer shift ‘δ’ and the values of QS

Acknowledgements

Author V.T. Vader wish to acknowledge his sincere gratitude to UGC-WRO, Pune (India) for financial assistance through ‘Minor Research Scheme F.No.47-2038/11 (WRO), 22.02.2012’. Author is also thankful to BARC, Mumbai for providing Mössbauer facility for samples analysis.

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A facile gel-combustion route for fine particle synthesis of spinel ferrichromite: X-ray and Mössbauer study on effect of Mg and Ni content

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Experimental details

X-ray diffraction study

Conclusions

Acknowledgements

Encycl. Conden. Matt. Phys.

J. Magn. Magn. Mater.

J. Rare Earth

Curr. Opin. Solid State Mater. Sci.

Solid State Sci.

Mater. Sci. Eng. B

J. Magn. Magn. Mater.

Mater. Chem. Phys.

Powder Technol.

J. Mater. Sci. Mater. Electron.