Influence of Cu dope on the structural behavior of MgFe2O4 at various temperatures
Introduction
Amongst the spinel ferrite families, magnesium ferrite (MgFe2O4) is a soft magnetic n-type semiconducting material that finds applications in the fields of heterogeneous catalysis, adsorption, sensors and magnetic technologies [1,2]. Numerous studies have been carried out on the spinel ferrites which had the general formula (M1-δFeδ)[MδFe2-δ]O4 due to their chemical and structural simplicity. The divalent metal element M (Mg, Zn, Cu, Fe, Co, Ni, or the mixture of them) can occupy either tetrahedral 8a (marked A) or octahedral 16b [marked B] sites of a spinel structure as depicted by the parentheses and brackets, respectively [[3], [4], [5]].
The crystal structure lies between a normal and an inverse spinel type that depends on the fraction of Fe3+-ions at the tetrahedral sites [6]. MgFe2O4 has a partially inverse spinel structure with the preference of Mg2+ cations mainly on octahedral sites [7,8], while copper ferrite (CuFe2O4) has an inverse spinel structure, in which all Cu2+ cations occupy octahedral sites [9,10]. Substitution of copper for MgFe2O4 resulted in the enhancement of permeability as well as magnetization values [11].
In our previous work [12], we performed a detailed investigation of the crystal structure of Cu doped MgFe2O4 at room temperature. In the present paper, structural properties of magnesium ferrite were explored at various temperatures. In order to test the phase stability and observe the structural evolution of the magnesium ferrite, some in-situ and ex-situ annealing experiments were performed under different temperatures, ranging from 298 to 753 K. Structural characteristics were studied by x-ray and neutron diffraction. Formation of ferrite was also confirmed by using Fourier-transform infrared spectroscopy (FT-IR). The main attention was paid to the evolution of the Mg1-xCuxFe2O4 under various annealing conditions.
Section snippets
Experimental
Mg1-xCuxFe2O4 type powder was prepared by a solid reaction method using MgO, CuO, Fe2O3 powder as a starting material [13]. Phase analysis of the samples were carried out using an x-ray powder diffractometer, Shimadzu XRD-7000 with CuKα radiation and λ = 1.5406 Å. Neutron diffraction measurements were performed on the HRFD (High Resolution Fourier Diffractometer) instrument at the IBR-2 reactor, Joint Institute for Nuclear Research, Dubna, Russia [9]. FT-IR spectra were recorded for all samples
Phase analysis
Fig. 1 shows the XRD patterns of the Mg1-xCuxFe2O4 samples with x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 which the peaks identified with Miller indices. The data showed intense sharp peaks and revealed well-crystalline single spinel structures. The result of phase analysis of patterns points out that the nominal composition structures with different concentrations have the cubic MgFe2O4 phase without any signature of impurity. A small amount of tetragonal CuFe2O4 phases were observed in the sample with
Conclusions
The temperature dependence of doping influence, crystal and magnetic structures above room temperature of Mg1-xCuxFe2O4, (х = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ferrites were studied in detail. No phase transition of doped and undoped MgFe2O4 was observed up to 753 K, beside cubic to the tetragonal structural transition of CuFe2O4 appeared at 473 K. The magnetization decreased with increasing temperature approaching zero at ∼753 K for Cu doped MgFe2O4, which had higher magnetic moments than undoped
Acknowledgements
The authors are grateful to Prof. A.M.Balagurov and Dr. I.A.Bobrikov for their help in neutron diffraction experiments on the IBR-2 (JINR, Russia) neutron source. This work was partially supported by the Mongolian Foundation of Science and Technology (Grant No: 2017/24).
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