Synthesis and characterization of ceria doped zinc ferrite nanopowdered crystallites

In this paper, we have reported the synthesis of fine crystallites of ceria doped zinc ferrite by co-precipitation and an open air heat treatment method. X-ray diffraction (XRD) gave the data for structural analysis. The XRD data were refined by Rietveld refinement using FullProf suite software. The evolution of the crystalline phases has been analyzed. The effect of precursor concentration is reflected in the resulting diffractogram. Structural characterization revealed the cubic structure of zinc ferrite with a space group of FD-3m(227) and the cubic structure of CeO with a space group of fm-3m(225). Structural parameters such as the lattice constant of the direct lattice, the lattice constant of the reciprocating lattice, lattice strain, covalent bond angle, dislocation density, crystallite size and Wyckoff positions were calculated.


Introduction
Recently modern nano-technologies in doped ferrites, transition metal oxides and their composites are attracting researchers. These metal oxide doped nano ferrites and their composites are widely used by experimental scientists and in theoretical studies. It would not be wrong to say that, compared to their complementary bulk materials, their properties such as optical, magnetic, electrical and catalytic properties make them technically useful [1]. Nanoscale materials attracted considerable attention in the decade before their remarkable and substantial use. When M contains nickel or zinc in the conventional formula i.e. MFe2O4, it can attract significant attention as a soft magnetic material (SMM) and has many potential applications [2]. These SMMs are usually spinel ferrites and possess a cubic configuration, where M denotes tetrahedral sites and Fe denotes octahedral sites. It is interesting that the nano-sized zinc ferrite (ZnFe2O4) has a compound backbone structure [3]. A composite backbone structure proved to be a commercially indispensable material and has many applications as a catalyst, as a gas sensing material, as a photocatalyst, and as absorbent devices [4]. Doping of various metal ions with ZnFe2O4 finds greater use in many fields [9]. Ceria has such a great impact on improving the technical properties of ZnFe2O4. Doping of ceria elements into SMMs find use in advanced technological processes like magnetostatic, electromagnetism, electrochemical etc. In general the addition of the host particle produces an isostructural disorder in external elements. Such a change in lattice may be due to the ion cation redistribution process. The researchers found that the specific surface area of a nanoferrite is fundamentally changed after the addition of the dopant, and this change proves useful with many novel demonstrations and novel applications. Therefore, materials with magnetic properties such as nanocomposites and CeO2 could be an option for better technology development, such as nanocomposites containing CuFe2O4 and CeO2 were found to be very useful in the field of energy storage. [5] The effect of gadolinium doping in nickel ferrite has been reported to some extent [6][7]. The reported doping of ceria in zinc ferrite proves to be a subject of better tradeoff in terms of modification in crystal geometry and shape that can be readily accepted with BET [8]. Recently the authors of this article have doped ceria in cobalt ferrite [14], and have shown that the dielectric constant and band gap of composites increases with increasing concentration of CeO2. This has also been proven that CeO2 absorbs many harmful gases. The research group has also shown that CeO2 is a better alternative to graded solar cells [6]. In some articles, the mentioned modifications were found when CeO2 was substituted in ZnFe2O4 [10]. Inspired by this, the authors dare to report the synthesis of CeO2 doped ZnFe2O4 nanocomposites using the co-precipitation technique. XRD has been used for the structural information of the samples in this paper. The Rietveld technique has been used to detect changes in atomic structure in the presence of nanoparticles. Rietveld purification is a good method of nanostructure characterization. It jointly gives detailed information about the crystallite size, network strain, and net parameters of the relative phases of a crystal lattice. Rietveld purification is also used for determination of the phase abundances in multiphase crystals. With this associated method, the balancing factor, forged shift, half-width, size parameters, and the nuclear location have also been derived. The report clearly describes the required modification or change in the lattice coordinates like direction constant, angles, bond length, bond parameters, etc. [13].

Experimental:
CeO2 is synthesized according to our previously published article [14] and zinc ferrite is manufactured according to our other published data [15].

XRD/Rietveld Refinement
The occurrence of non-amorphous phases of powder samples is determined by the XRD pattern ( Figure 1). All solid/powder samples are scanned at an angle of 20° to 80°. Mainly the current phases have been rectified ( Figure 2) using Rietveld refinement. GIXRD geometry was planned for given XRD pattern of powdered samples through Philips X-Ray diffractometer. All the difractograms were drawn at room temperature. [16] The diffraction pattern of well resolved peaks corresponding 2θ (glancing angle) ~18.32 ο ,28.60 ο , 30.20°, 33.14 ο , 35.58°, 43.28°, 47.58°, 53.61°,56.41 ο , 57.13°, 62.83°, 69.71 ο , 74.45°, 76.75 ο and 79.24°. The given values of angle 2θ were well-matched with the ZnFe2O4 ferrite [17]. The relevant data obtained from diffractogram for the ZnFe2O4 phase is given in In our earlier report [14] it shown that with increasing the ceria content, the lattice parameters (constants, angles) were found shortened. It was also described over there, that upper mentioned change was due to replacement of Zn ions in the CeO2 lattice. But here in this article similar results are probably due to defect formation and removal of oH ion from the lattice. [19,20]. To observe the effect of particular "Ce"(33%) doping in Zn(70%) and continuous heat increment, the well-known fulprof suit programme was used [21].
For the prepared sample i.e CeO2/ZnFe2O4 (powder nanocomposite) the Rietveld-refinement outline (using the FullProf suit software) shown in Figure- CeO2 has refined into a face centered cubic crystal geometry (phase1) by means of gap group Fm-3m and the crystal structure of ZnFe2O4 successfully refine in FCC cubic crystal geometry (phase-2) with space group Fd3m [24]. The refined direct cell parameters for CeO2 are found to be a=b=c=5.4044 and α=β=ϒ=90º. The direct cell volume of CeO2 was found to be 157.85 and the refined direct cell parameters for ZnFe2O4 are found to be a=b=c=8.3621, α =β =ϒ=90º and refined direct cell volume for ZnFe2O4 are found to be 584.72 which is shown in Table 4. The appropriate value of goodness of fit parameters are found to be χ2=3.54, Rwp= 16. 8, Rp=8.31, R.exp= 8.94, and bragg R factor for ZnFe2O4 is 7.17 and for CeO2 is 7.23 and Rf factor for ZnFe2O4 is 1.9 and for CeO2 is 2.1 which is shown in Table 5.

CONCLUSION
Nanopowdered crystallites of ceria doped zinc ferrite were prepared through the co-precipitation technique. XRD and Rietveld Refinement processes were used for the structural characterization of powdered composite material. The structure of crystal (CeO2) had cubic geometry with space group Fm3m and the structure of crystal(ZnFe2O4) had cubic geometry with space group Fd3m. The different characteristics FWHM, 2theta, d-spacing, particle size, and dislocation density value of ceria doped zincferrite nano sized powdered phases of prepared sample was obtained. The goodness factor and R parameters of ceria and zincferrite were calculated using full proof program and agreement between observed and calculated factors (R-factors) and χ 2 shows good fitting. The structural refinement of CeO2/ZnFe2O4 samples is in good agreement with XRD results of sample.

ACKNOWLEDGEMENTS
The authors are thankful to Dr. Narender Kumar Chauhan, Librarian GJUS&T Hisar.