3.1 XRD Study
XRD patterns of CCMF represent in Fig.2. These pattern indicate that the complex nature. These structural peaks are indexed such as (220), (311), (111), (422) etc are evidence polycrystalline phase and it has magnetic ordered spinel structure. For peak reflections such as (2 2 0); (4 0 0); (3 1 1); (2 2 2); (5 1 1); (4 2 2); (4 4 0) and (5 3 3) with FCC-structure but also for the existence of impurity peaks confirming the polycrystalline phase of the present samples [42]. The lattice constant, X-ray density, dislocation density, strain and crystallite size values determined by using (311) prominent peak. These parameters are calculated by following equations [48, 49],
Crystallite size
|
D = 0.9 λ/ β cosθ
|
[nm]
|
(1)
|
Lattice constant
|
a = [d2 (h2+K2+l2)] ½
|
[Å]
|
(2)
|
X-ray density
|
Dx=8M/Na3
|
[g/cm3]
|
(3)
|
Volume
|
V = a3
|
[Å] 3
|
(4)
|
Strain
|
ɛ = (β Cos θ)/4
|
[no unit]
|
(5)
|
The lattice constant (a) calculated by most intense peak (311) for CCMF is 8.368 Å due to incorporation of bigger ionic radius Mo3+ (0.69 Å) cations instead of comparatively small Fe3+ (0.64 Å) cations, which is in accordance with that stated in the literature [23,50]. By knowledge, Mo exist more chemical valance states such as Mo3+, Mo4+, Mo5+and Mo6+. Mo cations did not directly replace by Fe2+/Fe3+ actions. Hence, polycrystalline phase structure distorted or arose secondary phase in the materials (Fig.2). The First major effect of peaks in CCMF due to shifting of lower angel peaks on either side of prominent peak i.e. (311) with incorporation of Mo ions observed in the literature [44]. The second idea, when lattice constant increased due to migration of the larger ionic radius of Mo ions between two voids. However, note that there are differences in the ionic radius when that of Fe3+ is compared with either Mo3+ or Mo6+. The ionic radius of Fe3+ (0.64 Å) is smaller than that of Mo3+ (0.69 Å) and larger than that of Mo6+ (0.59 Å). Therefore, the lattice constant CCMF indicates the function of Mo ions incorporated ferrite. It exist lower valence state than Mo6+ state then only lattice increase can occur. Thus, the present data clearly indicate that the Mo exists in lower chemical valance state(s) while replacing/substituting for Fe3+ in the CCMF lattice. The observed lattice constant (8.368 Å) is attributed to difference in ionic radii such as Fe3+ (0.64 Å), Mo3+ (0.69 Å) Mo6+ (0.59 Å) [51, 52]. The crystallite size of CCMF is 16 nm. Therefore, if the crystallite size (16nm) is expected to decrease, the crystal axis ratio will increase as well. Molybdenum incorporated ZnFe2O4 employed by Zein K. Heiba and repotted crystallite size, strain, X-ray density, volume is (8.1-11.9) nm, (22-41), (5.59-5.773) respectively [33]. For complex valance state cations (Mo3+/ Mo6+) can raise a compression stress resulting in a lattice micro strain (CCMF=0.23009) preventing the grains from growing. It is therefore confirmed that in the materials, lattice strain is generated. A micro-strain (lattice strain) means that the distance between the respective crystal planes, which is not the same, probably because of the presence of defects and stress (magnetic properties). For expect the reduction of the crystallite size with Mo content to be associated with an increase of the micro-strain for the surface-induced stress effects. So, the crystallite size of CCMF is grater then Molybdenum doped ZnFe2O4. The density and atomic weight of Mo3+ are 10.28 g/cm3 and 95.94, which are greater than those of Fe3+ 7.874 g/cm3 and 55.845. Thus, the overall density increase of CCMF compounds can attribute to the fact that the density and atomic weight of Mo are higher than those of Fe for which the Mo ions are substituting or replacing in CCMF [21]. Furthermore, the crystallite sizes are in good agreement with the TEM analysis results of the CCMF. The volume of unit cell is 583.857Å3. It was observed that Fe2+ ions can be introduced into the cations Mo to give up the neutrality of charge in the ferrite materials.
3.2 FTIR study
The FT-IR spectra of CCMF showed in Fig.3, in which observe four characterizing peak between 400-4000 cm-1. There are two most intense peaks observed in spectra such as 471cm-1 and 550cm-1, which are corresponding to the tetrahedral and octahedral vibrational modes [38,39] respectively. Non magnetic metal like molybdenum (Mo) incorporated spinel ferrite; it shifts bands to the higher wave number. Hence peaks amplitude/intensity decreases for the lattice parameters modifications or crystal defects. The characteristic molybdenum (O-Mo-O) bands appear in the range 984 cm-1[38, 53, 54]. The shift in the bands positions can attribute to the reduction in lattice parameters for Mo doping [39]. Lattice parameter’s value depends of difference in ionic radii of Fe3+ and Mo5+ ions. Tetrahedral ionic radius of Mo5+ ions (0.46 Å) is smaller than the tetrahedral ionic radius of Fe3+ ions (0.49 Å) while the octahedral ionic radius of Mo5+ ions (0.61 Å) is larger than the octahedral ionic radius of Fe3+ ions (0.55 Å)[39]. The peak at 1079 cm−1 refers to C–H bending mode [53]. The peak at 1632 cm-1 assigned to C=O band stretching [39]. 2359-3363 cm-1 referring to the stretching vibration of O-H bands of water molecules [39, 55].
3.3 TEM & EDX study
Fig.4 shows the TEM microstructures of CCMF and more or less spherical aggregates with the size up to 50 nm. Since the relatively large thickness of the aggregates makes it difficult to observe the bulk particles, typical features on the edges of the aggregates can still be observed. There is obviously a different contrast to the matrix in certain individual crystallites, which suggests that they are made up of heavier elements than the rest of the matrix. The micrograph shows that two forms of nanoparticles are present. Dark contrast particles showed a spherical form with a random orientation and an average size of >50 nm, consisting in a CCMF ferrimagnetic phase in the structure [36]. For the CCMF sample a closer investigation into the HR-TEM image shows the presence of two types of crystallites that can be well correlated to the XRD observations. The high value of lattice micro-strain of the materials can be best explained on the basis of charge carrier hopping between Fe2+↔Fe3+, Co2+↔Co3+, Cu2+↔Cu3+ and Mo2+↔Mo3+ ions, so that the electric dipoles align themselves along the applied alternating field [24]. Fig. 4, the adequate content of both Mo and Co additives will obviously increase the grain size of the CCMF ferrites and do not shape clearly closed pores [55]. As shown in Fig.5, The presence of all the compounds i.e., Cu, Co, Mo, Fe, O and C confirmed the formation of nanocomposite Cu0.5Co0.3Mo0.2Fe2O4 (CCMF) and without any impurities, The Co, Mo, Cu and O signals are clearly defined, indicating the active processing of copper, cobalt, molybdenum and iron containing metal oxides. The Cu peak strength for the samples prepared using higher Cu precursor ratios has been increased.
3.4 VSM study
The magnetic properties modifications of CCMF depends crystallite size, cations orientations surface morphology and super-exchange interactions via the mediating oxygen O2- anions [39]. The magnetization curves showed in Fig.6, which explained ferrimagnetic behavior. For, Coercivity (Hc) of CCMF is 985.29 G. The higher coercivity value suggests that CCMF exhibit excellent soft ferrimagnetic properties [56]. This ferrimagnetic moment (μB =8.808E-3) exhibits for electron spin signature. Hence, the magnetization strongly affected by cation settlement between tetrahedral sites/voids (A) and octahedral sites/voids (B). According to Neel’s collinear model, three types of super exchange interactions involved such as A–B, A–A, and B–B. Here, A–B interaction is stronger than A–A and B–B interactions [41]. The saturation magnetization of CCMF is 0.20137emu/g. This lower magnetization exhibits by the substitution of Fe3+ by nonmagnetic Mo3+ ions at the B sites for ionic radius. As results migrations of Fe3+ in the B sites. It eliminates exchange (B-B) and super exchange (A-B) interactions [26, 57]. Similarly, same result was got for Mo doped ferrite nanoparticles [37, 40, 41]. For the present method, the exceptionally low magnetization values derive from two sources. Primary, the ferrimagnetic activity at the B site (Fe3+↔Mo6+) and secondary, the small size with the local and surface canting effects associated with it [39]. Saturation magnetization of the Mo doped ferrimagnetic signature suggested that it was attributable to the net magnetic moment of ions of opposite rotations in interstitial positions. The lower remnant magnetization (Mr =0.10608 emu/g) obtained by CCMF, which can be described by substituting fewer magnetic Mo6+ ions on the basis of magnetic dilution. Because of, density of Fe-ions is decreased at the tetrahedral site (A) when the Fe3+ ions (magnetic) are replaced by Mo6+ ions (nonmagnetic), resulting in a small value magnetic moment and remnant magnetization from review of ligature [56]. The remnant ratio of CCMF is 0.5267. If the residual ratio is greater than 0.5, compounds have a single magnetic domain instead of a multi-magnetic domain where the residual ratio is less than 0.5 [56]. Above said concept and summarized data widely agreed that the polycrystalline ferrites with FCC phase are greatly influenced by different intrinsic and extrinsic factors such as saturation magnetization (Ms), grain size, purity, shape of particle and particle distribution [41, 58]. By modified CCMF structure materials can improved Structural and magnetic properties of system. So, it has higher coercivity (985.29G) and can be used for cathode content Li-ion batteries [23].