Effect of sintering temperature and thermoelectric power studies of the system MgFe2−xCrxO4

doi:10.1016/j.solidstatesciences.2009.09.005

Solid State Sciences

Volume 11, Issue 12, December 2009, Pages 2075-2079

https://doi.org/10.1016/j.solidstatesciences.2009.09.005 Get rights and content

Abstract

Mixed metal oxides showing the spinel structure exhibit interesting structural and electrical properties. Substances with specific compositions in the system MgFe_2−xCr_xO₄ were synthesized by the simple co-precipitation method and have been investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM) to study the effect of temperature on the size of particles and grains. The infrared spectrum shows, two strong bands around 600 and 500 cm⁻¹. An elemental composition of one of the samples, MgFeCrO₄ was found by energy dispersive X-ray spectroscopy (EDS). The thermoelectric power measurements carried out from room temperature to 500 °C, show both n-type and p-type behavior.

Graphical abstract

Introduction

Ferrites have been used by various industries as a catalyst for some industrially important catalytic reactions. The interesting physicochemical properties of ferrospinels arise from their ability to distribute the cations among the available tetrahedral (A) and octahedral [B] sites [1], [2], [3]. Magnesium ferrite is a magnetic material having an inverse spinel structure of which the degree of inversion depends upon the heat treatment. At present, several chemical methods including the solid state reaction, co-precipitation, sol–gel, citrate method have been developed to synthesize small particle sized ferrites [4], [5], [6].

The conventional ceramic method for the preparation of ferrites has certain limitations such as long heating schedule at high temperatures. Hence, in the present investigation chromium substituted magnesium ferrites have been prepared by the simple co-precipitation technique. The main important topic in the present study concerns the substitution of Cr³⁺ and the heat treatment on structure and thermoemf properties. The thermoelectric power studies also give the information about the type of conductivity, weather it is n-type or p-type.

Section snippets

Experimental

For the purpose of this investigation, various compositions of MgFe_2−xCr_xO₄ (x = 0.0, 0.5, 1.0, 1.5 and 2.0) were prepared by the simple co-precipitation method [7], [8]. The high purity A.R. grade magnesium chloride, chromium chloride and iron chloride were weighed carefully to have the desired stoichiometric proportion. A mixed solution of the above chlorides was prepared in double distilled water. The precipitation was carried out at a controlled pH of ∼9.0 using a 10% NaOH solution. It was

X-ray diffraction studies

X-ray diffraction patterns of MgFeCrO₄ at different temperatures are presented in Fig. 1. The peaks are indexed to the characteristic planes of pure spinel cubic structure. The diffraction peaks are found to be sharp and their intensity increases with increase in the sintering temperature. No other phase has been detected and (311) reflections appear to be more intense [9], [10], [11] consistent with observations for face centered cubic spinel.

Because the (311) diffraction peak at 900 °C is

Conclusions

The system MgFe_2−xCr_xO₄ is synthesized by the simple co-precipitation method at controlled pH and exhibits the cubic spinel structure. The effect of sintering temperature on the observed structure influences the size of particles and consequently the grains. The calculated site radii and bond lengths show that the octahedral site radius is larger than the tetrahedral site. The FTIR spectrum shows two strong bands ν₁ and ν₂ in the expected region and the difference in their observed band

Acknowledgements

Authors PPH and VTV wish to acknowledge their sincere gratitude to UGC for Major Research Project [F. No. 32-289/2006 (SR)] New Delhi, India for their financial support.

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Effect of sintering temperature and thermoelectric power studies of the system MgFe2−xCrxO4

Abstract

Graphical abstract

Introduction

Section snippets

Experimental

X-ray diffraction studies

Conclusions

Acknowledgements

Mater. Lett.

Appl. Catal. A. General

J. Mol. Catal. A: Chemical

Mater. Chem. Phys.

Mater. Lett.

Mater. Chem. Phys.

J. Magn. Magn. Mater.

Mater. Lett.

J. Alloys Compd.

Philips Res.

Effect of sintering temperature and thermoelectric power studies of the system MgFe_2−xCr_xO₄