Cation Distribution and Rietveld Refinement of Zinc substituted Magnesium Ferrichromate

 

Paresh More*, Kundan Patil, Namrata Ghag, Juhi Suhanda

Department of Chemistry., K.E.T’S V.G.Vaze College, Mulund(E), Mumbai-400081, Maharashtra (MS) India

*Corresponding Author E-mail: paresh.m34@gmail.com

Zinc substituted Magnesium ferrichromate Mg_1-x­Zn_xFeCrO₄ (x = 0.0 to x = 0.9)) system was synthesized by co-precipitation method. The structural, spectral and morphological properties of ferrites were determined by X – ray diffraction (powder XRD), IR and Scanning Electron Microscopy (SEM). Crystal lattices parameters increases with the increase in the zinc substitution in the system .Two absorption bands in the FTIR, in the range of 400 cm^-1 to 4000 cm^-1 were observed due to tetrahedral (A) and octahedral (B) stretching vibration. Force constant for tetrahedral site (K_t) and octahedral site (K_o) were calculated from IR. SEM data suggests surface morphology to be nearly spherical and agglomerates. Cation distribution in ferrites was studied using Bertaut method. Prepared samples shows cubic spinel structure, these observations were supported by Rietveld refinement.

 

 

INTRODUCTION:

Nanomaterials have drawn a lot of scientific and technological attention because of their distinct properties when compared to their bulk compounds [1-6]. The properties of ferrites can be altered by tuning the physical and chemical properties of the materials and change in properties depends on many factors which include the method of preparation, reaction conditions like sintering temperature and time, rate of heating and grinding time[7-9]. Spinel ferrites are well known for their remarkable magnetic, optical and electrical properties when they are at a nanometre scale [10-11].

 

 

Physico-chemical properties of nano ferrites can be improved by doping. Researchers have shown that the structural [12], electrical [12-14], magnetic [15-16], optical [13] properties shows appreciable changes after doping. The synthesis of system Mg_1-x­Zn_xFeCrO₄ is reported by Gismelseed et al using ceramic method [17]. However detail investigation of the system was not carried out. Among the various synthetic routes considered by Gold Stein and Tseung [18], hydroxide co- precipitation is the best for achieving high surface area for the spinel catalyst[19]. To the best of our knowledge we are the first group reporting synthesis of Mg_1-x­Zn_xFeCrO₄ system by co- precipitation method, which has a lot of advantages over other methods. Synthesize of the system Mg_1-x­Zn_xFeCrO₄ was planned as it has lot of industrial applications[20]. Also it is well known fact that Zn²⁺ ions are diamagnetic in nature which can be used in developing technologically important materials. Their substitution may induce important changes in one’s properties as cation distribution in between available A and B sites changes which lead to changes in properties of ferrites.

In this paper, we describe the detailed study of Mg_1-x­Zn_xFeCrO₄ system synthesised by co- precipitation method, The cation distribution by Bertaut method and structure refinement of the system by Rietveld analysis. Ferrites were characterised by XRD, SEM and IR.

 

EXPERIMENTAL:

All the reagents used were of analytical grade. The system Mg_1-x­Zn_xFeCrO₄ with x varying from 0.0 to 0.9 was synthesized using co- precipitation method [21]. The starting materials were Zinc nitrate (Zn(NO₃)₂.6H₂O), Magnesium sulphate (MgSO₄.7H₂O), Chromium Nitrate (Cr(NO₃)₃.9H₂O) and Iron Nitrate(Fe(NO₃)₃.9H₂O) Compounds were washed with distilled water till they are free from nitrates and sulphates anions. The compounds were oven dried at 373K and then calcined at 873K in muffle furnace for 5 hrs. Sintered samples were powdered for X-ray investigation. Powder was X-ray examined by Phillips X- ray diffractometer using Cu-Kα radiation having wavelength (1.54 A°) at TIFR Mumbai.

 

The XRD data was processed in order to analyze all the samples using Full prof (FP Suite TB) for the structure refinement using Rietveld method. Rietveld refinement of first samples was started with origin at -3m in 32e, the space group Fd-3m, A site in 8f, and B site in16c. The first stage involves refinement of the global parameters which is 2θ- zero and the background. In the next stage, the other parameters such as site occupancy, lattice parameters and atomic coordinates were refined.

 

IR spectra were recorded in the range of 400 cm^-1 to 4000 cm^-1 at room temperature using Shimadzu model miracle 10. However in the ferrites the region of the interest is from 400 cm^-1 to 1000 cm^-1, hence spectra were analyzed in the region from 400 cm^-1 to 1000 cm^-1.

 

The microstructure and morphology of sintered powder were characterised by Scanning Electron Microscopy (SEM) (Model ZEISS ULTRA FESEM) at TIFR, Mumbai.

 

RESULTS AND DISCUSSIONS:

XRD:

The X-ray diffraction pattern of the system Mg_1-x­Zn_xFeCrO₄ (x=0.0, 0.1, 0.3, 0.5, 0.7, 0.9) for all the samples is represented in the figure 1. The pattern confirms formation of single phase cubic spinel structure.

 

The cation distribution in the present work can be obtained from X-ray diffraction pattern. In the present work Bertaut method [22] was used to determine the cation distribution. Excellent information on cation distribution cab be achieved by comparing the intensity ratio (experimental and calculated) for reflections whose intensities (i) vary with the distribution of cations in opposite ways (ii) are almost independent of the oxygen position parameter and (iii) do not significantly differ.

 

The results of cation distribution are given in the table 1. Fraction of Fe³⁺ ions are found on both the sites with the increase in the concentration of zinc occupancy of Fe³⁺ in the B site increases. Mg²⁺ions occupy A as well as B site however it shows maximum occupancy at B site. This is due to larger ionic radius of Zn²⁺ ion (0.82 Å), which when substituted in the lattice reside on the tetrahedral site and displace the smaller Fe³⁺ ions (0.67 Å) from the tetrahedral sites to the octahedral sites at the expense of Mg²⁺ ions (0.66Å). Zn²⁺ ions occupy tetrahedral A site due to its large ionic radius (0.82 Å) with only one exceptional in the last compound (x=0.9) in which a very small occupancy of Zn²⁺ ions are observed at the B site. Cr³⁺ ions replaces Fe³⁺ from the octahedral sites this is because of (Cr³⁺ 6/5 ∆_o, Cr³⁺O∆_o)  morefavourable crystal field effects[23].The data given in the table 1 shows that the octahedral sites is predominantly occupied by Cr³⁺ ions, this is simply because of large octahedral site energy.

 

Using radius of oxygen ion R_o=1.32, radius of tetrahedral A site (r_A) and the value of lattice constant a, the oxygen positional parameter u can be evaluated from following expression. [24]

 

 

The value of oxygen positional parameters increases from 0.3869 to 0.3925 is tabled in table 1. In most of the oxide spinel, the size of oxygen ions is found to be larger than the metallic ions. In spinel structures the value of oxygen positional parameter is nearly equal to 0.375 Å. To have this value the arrangement of O^2- ions should be equal, exactly cubic like packing, however in actual spinel lattice the ideal pattern gets slightly deformed.

 

Our value of oxygen positional parameters (u) is greater than ideal value this may be due to various reasons, experimental error or measurement errors. In most samples, u > 0.375 is obtained due to small displacement of anions because of expansion of tetrahedral interstitials. In this system, u > 0.375 which may be due to the displacement of anions from the ideal position [25]. The disturbance in the lattice is confirmed from the data of lattice constant and oxygen positional parameter (u).

 

Figure 1: The X-ray diffraction pattern of the system Mg_1-x­Zn_xFeCrO₄ (x= 0.0, 0.1, 0.3, 0.5, 0.7, 0.9)

 

 

Figure 2 is the representative spectra of Rietveld refined XRD of the sample with concentration x=0.5.

Table No.1. Cation Distribution of tetrahedral A-site and B-site, mean ionic radii of tetrahedral A (r_A) site and octahedral B (r_B) site, theoretical lattice constant (a_th) and oxygen position parameter (u) Of Mg_1-xZn_xFeCrO_4.

Comp.	Cation Distribution		rA	rB	ath	u
X	Tetrahedral A-Site	Octahedral B-Site	Å	Å	Å	Å
0.0	Mg0.2Cr0.3Fe0.5	Mg0.8Cr0.7Fe0.5	0.671	0.680	8.398	0.3869
0.1	Mg0.1Zn0.1Cr0.3Fe0.5	Mg0.8Cr0.7Fe0.5	0.680	0.680	8.412	0.3873
0.3	Mg0.05Zn0.3Cr0.2Fe0.45	Mg0.65Cr0.8Fe0.55	0.709	0.674	8.442	0.3887
0.5	Zn0.5Cr0.1Fe0.4	Mg0.5Cr0.9Fe0.6	0.737	0.669	8.472	0.3902
0.7	Zn0.7Cr0.05Fe0.25	Mg0.3Cr0.95Fe0.75	0.767	0.663	8.502	0.3917
0.9	Zn0.8Cr0.05Fe0.15	Mg0.1Zn0.1Cr0.95Fe0.85	0.781	0.659	8.513	0.3925

 

The refinement of the system was continuously carried out till convergence was achieved with a goodness factor less than 2.30. Table 2 contains values of discrepancy factor (R_wp) expected (R_exp) values and the index of goodness of fit(x²),Refined values of Rietveld refinement are found to be in very close agreement with the values reported in the literature for other ferrite system [26,27].

 

Lattice constant (a) was calculated using Rietveld refinement and the values of lattice constant are listed in table 2. The steady increase in the lattice constant with increase in Zn²⁺ concentration is due to its larger ionic radius of Zn²⁺ ion (0.82 Å) ,which when substituted in the lattice reside on the tetrahedral site and displace the smaller Fe³⁺ ions (0.67 Å) from the tetrahedral sites to the octahedral sites at the expense of Mg²⁺ ions (0.66 Å). The results are in close agreement with the earlier values reported in literature [28-29]

 

Table 2. Discrepancy Factor (Rwp) expected values (Rexp), goodness of fit factor (χ²) and lattice constant (a).

Compound x	Rwp (%)	Rexp (%)	χ2	a(A0)
0.0	1.0	0.670	2.24	8.28462
0.1	0.98	0.658	2.25	8.32200
0.3	1.02	0.759	1.78	8.33974
0.5	1.01	0.7979	1.58	8.34500
0.7	1.00	0.6823	2.16	8.37416
0.9	0.487	0.3777	1.66	8.37991

 

FTIR Analysis:

The Infra red spectra was recorded in the range of 400 cm^-1 to 4000 cm^-1. However in spinels and ferrites the range from 400 cm^-1 to 1000 cm^-1 is sufficient. Hence spectra were scanned in the range from 400 cm^-1 to 1000 cm^-1. IR spectra give additional information such as valence state and various vibrational modes in the crystal lattice. Two most prominent absorption bands were observed in the range of υ₁ 614 cm^-1 to 678 cm^-1 and υ₂ 414 cm^-1 to 428 cm^-1. These bands were observed due to stretching vibration of tetrahedral metal ion and due to the divalent metal ion-oxygen complex of the the octahedral sites [30-31]. Absorption bands observed in the above range is indication of single phase spinel structure. The bands υ₁ and υ₂ are responsible for the intrinsic vibration of tetrahedral site and octahedral sites [32].

 

On observing the IR spectra carefully we can conclude that tetrahedral complexes (υ₁) have very intense absorption band as compare to octahedral (υ₂) complex. This observation is a consequence of first selection rule.

 

From the figure it is clear that with the increase in the zinc concentration the absorption bands shift slowly towards the low frequency region. It may happen due to addition of larger Zn²⁺ ion which increases the bond length. Similar observations were reported by Sheikh et al. [25]

 

By keeping other independent parameters constant we can determine force constant. The force constant of tetrahedral site (k_t) as well as octahedral sites (k_o) were calculated by the method suggested by Waldron [32].

Force constant k_t as well as k_o for respective site can be calculated by using following equation.

 

 

 

M₁ and M2 are molecular weights of the cations on A and the cations on B site respectively. Using the formula given by Gorter [33] the bond length R_A and R_B were calculated. The molecular weights M₁ and M₂ of the tetrahedral and octahedral sites were calculated using the cation distribution by Bertaut method. The data is tabled in table 3. The bond length R_A and R_B, the force constants k_t and k_o are given in table 3.It is clear from the values of k_t and k_o that the force constant are found to increase, whereas value of R_B initially increases and then with increase in zinc content R_B decreases. It is very well known fact that in the IR studies that there is inverse relationship between force constant and bond length [34].

 

Figure 3: IR spectra of the system Mg_1-x­Zn_xFeCrO₄(x= 0.0, 0.1, 0.3, 0.5, 0.7, and 0.9)

Table 3. Band Positions (υ₁and υ₂), force constants (K_o and K_t), and bond lengths (R_A and R_B) of Mg_1-xZn_xFeCrO_4.

Compound x	υ1 cm-1\Tetrahedral	υ2 cm-1 Octahedral	Ko x 105 dyne/cm	Kt x 105 dyne/cm	RA(A0)	RB(A0)
0.0	570	427	0.811x 105	1.197x 105	0.6712	0.6795
0.1	590	428	0.814x 105	1.392x 105	0.6804	0.6795
0.3	595	421	0.829x 105	1.520x 105	0.7080	0.6748
0.5	595	414	0.841x 105	1.624x 105	0.7372	0.6692
0.7	600	418	0.914x 105	1.709x 105	0.7665	0.6635
0.9	600	425	1.015x 105	1.73x 105	0.7810	0.6592

 

 

Figure 4: SEM analysis of the system Mg_1-x­Zn_xFeCrO₄(x= 0.0, 0.1, 0.3, 0.5, 0.7, and 0.9)

 

SEM:

The morphological analysis was performed using SEM (Scanning Electron Microscope). The secondary electron images were taken at different magnification to study the morphology of the material. Fig. shows micrograph of the sample with different zinc substitutions. SEM analyses revealed that the particle morphologies of all the products have agglomeration to some extent. The spherical shaped nano size particles were successfully prepared as shown in figure 4. These particles are in the form of big aggregates consisting of nano particles of spherical shape.

CONCLUSION:

Zinc substituted MgFeCrO₄ ferrites were synthesized at relatively low temperature. Doping of zinc in the above system has induced appreciable changes in the structural properties of the ferrites. Rietveld refined XRD data and intensity calculation data by Bertaut method are in very close agreement in cation distribution and lattice constant. Crystal lattice parameter increases with the increase in the concentration of zinc substitution. Cation distribution suggests that with the increase in zinc substitution Mg²⁺ and Cr³⁺ shows strong preference to occupy B site where as Zn²⁺ shows very strong preference to occupy A site. The IR spectra support formation of spinel structure and cation distribution. From the SEM analysis it is clear that ferrites are nano particles and are spherical in shape.

 

REFERENCES:

1.        Kaviyarasu K, Manikandan E, Paulraj P et al (2014) One dimensional well-aligned CdO nanocrystal by solvothermal method. J Alloys Comp 593:67–70. doi:10.1016/j.jallcom.2014.01.071

2.        Kaviyarasu K, Manikandan E, Kennedy J, Jayachandran M (2014) Quantum confinement and photoluminescence of well-aligned CdO nanofibers by a solvothermal route. Mater Lett 120:243–245. doi:10.1016/j.matlet.2014.01.048

3.        Kennedy J, Leveneur J, Williams GVM et al (2011) Fabrication of surface magnetic nanoclusters using low energy ion implantation and electron beam annealing. Nanotechnology 22:115602. doi:10.1088/0957-4484/22/11/115602

4.        Kennedy J, Williams GVM, Murmu PP, Ruck BJ (2013) Intrinsic magnetic order and inhomogeneous transport in Gd-implanted zinc oxide. Phys Rev B 88:214423. doi:10.1103/PhysRevB.88.214423

5.        Kaviyarasu K, Manikandan E, Kennedy J, Maaza M (2015) A comparative study on the morphological features of highly ordered MgO:AgOnanocube arrays prepared via a hydrothermal method. RSC Adv 5:82421–82428. doi:10.1039/c5ra15132e

6.        Kasinathan K, Kennedy J, Elayaperumal M, Henini M, Malik M (2016)Photodegradation of organic pollutants RhB dye using UV simulated sunlight on ceria based TiO₂ nanomaterials for antibacterial applications. Sci Rep 6:38064–38076. doi:10.1038/srep38064

7.        Goldman, A: Modern Ferrite Technology. Van Nostrand, Reinhold,New York (1990)

8.        Chen, CW: Magnetism and Metallurgy of Soft Magnetic Materials. North-Holland, Amsterdam (1990)

9.        Batoo, KM: Structural and electrical properties of Cu doped NiFe2O4 nanoparticles prepared through modified citrate gel method. J. Phys. Chem. Solids 72, 1400–1407 (2011)

10.     Joshi S, Kumar M, Chhoker S et al (2017) Effect of Gd³⁺ substitution on structural, magnetic, dielectric and optical properties of nanocrystalline CoFe₂O₄. J Magn Mag Mater 426:252–263

11.     Vadivela M, Babua RR, Ramamurthib K, Arivanandhanc M (2016) CTAB cationic surfactant assisted synthesis of CoFe₂O₄ magnetic nanoparticles. Ceram Inter 42:19320–19328

12.     Agrawal S, Parveen A, Azam A (2016) Structural, electrical, and optomagnetic tweaking of Zn doped CoFe2-xZnxO4-δ nanoparticles. J Magn Mag Mater 414:144–152

13.     Manikandana A, Vijaya JJ, Kennedy LJ, Bououdina M (2013) Microwavecombustion synthesis, structural, optical and magnetic properties of Zn_1−xSr_xFe₂O₄ nanoparticles. Ceram Inter 39:5909–5917

14.     Rathi R, Neogi R (2016) Structural, Electric and magnetic properties of Titanium doped Ni-Cu-Zn Ferrite. Mater Today 3:2437–2442

15.     Choodamani C, Nagabhushana GP, Ashoka S et al (2013) Structural and magnetic studies of Mg_(1−x)Zn_xFe₂O₄ nanoparticles prepared by a solution combustion method. J Alloys Compd 578:103–109

16.     Gabal MA, Al-Juaid AA, Al-Rashed SM, et al. Synthesis, characterization and electromagnetic properties of Zn-substituted CoFe₂O₄ via sucrose assisted combustion route. J Magn Mag Mater. 2016; doi.org/10.1016/j.jmmm.2016.10.147.

17.     A. M. Gismelseed, K. A. Mohammed, A. D. Al-Rawas, A. A. Yousif, H. M. Widatallah, M. E. Elzain, Hyperfine interaction doi: 10.1007/S10751-013-1003-6

18.     J. R. Goldstein and A. C. C. Tseungj.Catal. 32,452 (1974).

19.     Emilia Zachanowicz, Aleksander Zięcina, Paulina A. Mikołajczyk, Krzysztof Rogacki, MałgorzataMałecka, Krzysztof Marycz, Monika Marędziak, BłazejPoźniak, Marta Nowakowska, Marta Tikhomirov, Julia Miller, Rafał J. Wiglusz, Robert Pązik. 2016. Cytotoxic Effects of Co 1- x Mn x Fe 2 O 4 Ferrite Nanoparticles Synthesized under Non-Hydrolytic Conditions (Bradley's Reaction) - In Vitro. European Journal of Inorganic Chemistry .         

20.     Koijima H; In; Wohlfarth,E.P.(ed.) Ferromagnetic materials: A handbook of properties of magnetically vordered substances,Vol.3. North Holland, Amsterdam (1982)

21.     G.R.Dube and V.S.Darshane, Bull.Chem.Soc. Japan, 64, (1991), 2449

22.     L. Weil, E. F. Bertaut, and L. Bochirol, “Propriétésmagnétiques et structure de la phase quadratique du ferrite de cuivre,” Journal de Physique et Le Radium, vol. 11, no. 5, pp. 208–212, 1950.

23.     A. Tomas, P. Laruelle, J. L. Dormann, and M. Nouges, “Structure of pentasodium dihydrogen orthophosphate diphosphate(V), Na₅H₂(PO₄)(P₂O₇),” Acta Crystallographica, vol. C39, pp. 1613–11615, 1983.

24.     K. J. Standley, Oxide Magnetic Materials, Clarendon Press, Oxford, UK, 1972.

25.     M. U. Rana, M. Islam, and T. Abbas, “Cation distribution and magnetic interactions in Zn-substituted CuFe₂O₄ ferrites,” Materials Chemistry and Physics, vol. 65, no. 3, pp. 345–349, 2000.

26.     S. M. Patange, S. E. Shirsath, S. S. Jadhav, K. S. Lohar, D. R. Mane, and K. M. Jadhav, “Rietveld refinement and switching properties of Cr³⁺ substituted NiFe₂O₄ ferrites,” Materials Letters, vol. 64, no. 6, pp. 722–724, 2010.

27.     A. K. M. Zakaria, M. A. Asgar, S. G. Eriksson, F. U. Ahmed, S. M. Yunus, and A. K. Azad, “Preparation of Zn substituted Ni-Fe-Cr ferrites and study of the crystal structure by neutron diffraction,” Materials Letters, vol. 57, no. 26, pp. 4243–4250, 2003.

28.     Hankare, P.P., Vader, V.T., Sankpal, U.B., Gavali, L.V., Sasikala, R., Mulla, I.S.: Solid State Sci. 11, 2075 (2009)

29.     Anantharaman, M.R., Jagatheesan, S., Malini, K.A., Sindhu, S., Narayanasamy, A., Chinnasamy, C.N., Jacobs, J.P., Reijne, S., Seshan, K., Smits, R.H.H., Brongersama, H.H.: J. Magn. Magn. Mater. 189, 83– 88 (1998)

30.     A. M. Shaikh, S. A. Jadhav, S. C. Watawe, and B. K. Chougule, “Infrared spectral studies of Zn-substituted Li-Mg ferrites,” Materials Letters, vol. 44, no. 3, pp. 192–196, 2000.

31.     D. Ravinder, “Far-infrared spectral studies of mixed lithium-zinc ferrites,” Materials Letters, vol. 40, no. 5, pp. 205–208, 1999.

32.     R. D. Waldron, “Infrared spectra of ferrites,” Physical Review, vol. 99, no. 6, pp. 1727–1735, 1955.

33.     E. W. Gorter, “Saturation magnetization and crystal chemistry of ferrimagnetic oxides. I. II. Theory of ferrimagnetism,” Philips Research Reports, vol. 9, pp. 295–320, 1954.

34.     A. Pradeep, P. Priyadharsini, and G. Chandrasekaran, “Sol- gel route of synthesis of nanoparticles of MgFe₂O ₄ and XRD, FTIR and VSM study,” Journal of Magnetism and Magnetic Materials, vol. 320, no. 21, pp. 2774–2779, 2008.

 

 

 

 

 

 

Received on 08.12.2017         Modified on 12.01.2018

Accepted on 28.02.2018         © AJRC All right reserved