The Electrical and Optical Properties of Zn0.5Li2xMg0.5-xFe2O4 Lithium Doped Nanoparticle Prepared by Coprecipitation Method

Nisreen A. Elthair^1,2, Eltayeb M. Mustafa¹, Abdelrahman A. Elbadawi^1,3

¹Department of Physics, Faculty of Science and Technology, Al Neelain University, Khartoum, Sudan.
²Department of Physics, Faculty of Science, Jazan University, Jazan, KSA.
³Faculty of Basic Studies, Future University, Khartoum, Sudan.

DOI: 10.4236/ojapps.2020.109039                

Abstract

In this study, nano ferrite materials were produced to replace costive industrial materials [1]. Ferrite nanoparticles are the interesting material due to their rich and unique physical and chemical properties. They find applications in catalysis, bio-processing, medicine, magnetic recording, adsorption, devices etc. Using co-participation method, five nano ferrite samples Zn_0.5Mg_0.5-xLi_2xFe₂O₄ (x = 0.00, 0.10, 0.20, 0.30 and 0.40) were prepared. The electrical and optical properties of the Zn_0.5Mg_0.5-xLi_2xFe₂O₄ samples were studied using the Ultraviolet-visible (UV-Vis) spectroscopy. The results verified that the formation of the absorption coefficient of the five samples of Zn_0.5Mg_0.5-xLi_2xFe₂O₄ increased with the increase of Lithium (Li_2x). The energy band gap of the Zn_0.5Mg_0.5-xLi_2xFe₂O₄ samples ranged from 3.28 to 3.12 eV [1]. The extinction coefficient (K) for five samples of Zn_0.5Li_2xMg_0.5-xFe₂O₄ increased with the increase of Lithium (Li_2x) at 338 nm from 0.074 to 0.207. The high magnitude of optical conductivity is (1.34 × 10¹² sec^-1) and the maximum value of electrical conductivity is 42 (Ω^.cm)^-1. This may due to the electrical and optical properties of lithium.

Keywords

Zn0.5Mg0.5-xLi2xFe2O4, Nano Ferrites, UV.vis, Co-Precipitation, Electrical Proper-ties, Optical Properties

1. Introduction

Particles in the size range of approximately 1 - 100 nm can display novel optical, electric, magnetic properties because of quantum confinement and surface effects that may find many important technological applications [2] [3] [4]. Nanotechnology is well-known as a very important key technology in science. In the field of material science, Ferrites are well-known magnetic nanomaterial’s intensively studied as a recording media due to their superior physical properties [5] [6] [7]. These properties make ferrites an ideal candidate for technical applications such as magnetic resonance imaging enhancement, catalysis, sensors and pigments [8]. Spinel nano ferrites (AB₂O₄) are materials of today’s research due to their amazing structural, dielectric, electrical and magnetic properties [9]. Such properties are dependent on the nature of cations, their charges and their distribution among tetrahedral (A) and octahedral (B) sites [10]. Various physical and chemical methods of preparation have been developed to achieve nano-sized ferrite particles such as sol-gel [11], chemical co-precipitation [12], hydrothermal [13], and chemical combustion route [14]. Among them, the chemical co-precipitation method seems to be the most convenient method for the synthesis of Zn-Co-Mg ferrites. It is very simple and has better control over the crystalline size and other properties of the materials [15]. In this work, Zn_0.5Mg_0.5−xLi_2xFe₂O₄ nano ferrite where (x = 0.1, 0.2, 0.3, 0.4 and 0.5) was synthesized using co-precipitation methods. Ultraviolet-visible spectrometer (UV) was used to study the optical, electric and magnetic properties of nanoparticles [16].

2. Materials and Methods

Zn_0.5Mg_0.5−xLi_2xFe₂O₄ nanoparticles samples (x = 0.00, 0.10, 0.20, 0.30 and 0.40) were studied by the co-precipitation method [1]. The raw stoichiometric materials are FeCl₃, MgCl₂∙6H₂O, LiCl∙H₂O, ZnCl₂ with high pure, NaOH was used to found the required solutions with required molarities. Firstly, the solution of MgCl₂∙6H₂O 0.2 M (25 ml), ZnCl₂ and FeCl₃ 0.4 M (25 ml) were mixed, next, slowly added to NaOH solution with stirring to obtain a mixture of pH 11 - 12. The colloid solution was kept in a water bath at 80˚C for 1 hrs to the removal of NaCl₂ and H₂O from the powder. The produced powder was washed by deionized water until the filtrate had a pH 7. Then the samples were dried and grinned to absolute powder and annealed to 450˚C for 6 hrs in temperature-controlled muffle furnace Vulcan A-550 at a heating rate 10˚C/min. The absorption of a solution with different concentrations was calculated using UV min 1240 spectrometer Shimadzu.

3. Results and Discussion

UV-VIS absorbance behaviour of curves was found to be the same for five samples of Zn_0.5Li_2xMg_0.5−xFe₂O₄; as shown in Figure 1. The figure shows the relation between absorbance and wavelengths for five samples of Zn_0.5Li_2xMg_0.5−xFe₂O₄. It depicts the rapid increase of the absorption at wavelengths 340 nm. It indicated an Lithium index (Li_2x) in the absorbance value, as the absorbance value increases with the increase of Lithium index (Li_2x).

Absorption coefficient (α): It describes how much light of a given color is absorbed by a material of a given thickness. The absorption coefficient (α) of the five prepared samples (Zn_0.5Li_2xMg_0.5−xFe₂O₄) was found using the following relation:

$\alpha =\frac{2.303xA}{t}$

where (A) is the absorbance and (t) is the optical length in the samples. Figure 2 shows that the Zn_0.5Li_2xMg_0.5−xFe₂O₄ plot of (α) with wavelength (λ) was the top among the five samples. The highest value of (α) for all samples was in the U.V region (340 nm). This means that the transition must be corresponding to a direct electronic transition, and the properties of this state are important since they are responsible for electrical conduction. Also, this figure shows that the value of (α) for the five samples increases with the increase of the Lithium index (Li_2x), which explains that lithium has a high absorbency [17] [18].

Figure 1. The relation between absorbance and wavelengths of Zn_0.5Li_2xMg_0.5−xFe₂O₄ samples.

Figure 2. The relationship between absorption coefficient (α) and wavelengths of ZnLi_2xMg_0.5xFe₂O₄ samples.

Extinction coefficient (K): It is a measure of light lost due to scattering and absorption per unit volume. Extinction coefficient (K) was calculated using the relation The variation at the (K) values as a function of (λ) for five samples of (Zn_0.5Li_2xMg_0.5−xFe₂O₄) is shown in Figure 3, where it is observed that the spectrum shape of (K) as the same shape of (α). The Extinction coefficient (K) for five samples of Zn_0.5Li_2xMg_0.5−xFe₂O₄ in Figure 3 indicated that the value of (K) at the wavelength depends on the samples treatment method, where the value of (K) at 338 nm for Zn_0.5Mg_0.5Fe₂O₄ sample equals 0.074 while it was 0.207 for the other sample (Zn_0.5Li_0.1Mg_0.8Fe₂O₄) at the same wavelength. The Extinction coefficient (k) increased with the increase of Lithium index (Li_2x) in the Zn_0.5Li_0.2xMg_0.5−xFe₂O₄ samples.

The optical energy gap (E_g): It is the threshold for photons to be absorbed. The optical energy gap (E_g) has been calculated by the relation (αhυ)² = C (hυ – E_g) where (C) is constant. By plotting (αhυ)² vs photon energy (hυ), as shown in Figure 4 for the five prepared samples and by extrapolating the straight thin portion of the curve to intercept the energy axis, the value of the energy gap has been calculated. In this figure, the value of (E_g) for Zn_0.5Mg_0.5Fe₂O₄ sample was (3.282) eV while it was (3.121) eV for the Zn_0.5Li_0.8Mg_0.1Fe₂O₄ sample. The decrease of (E_g) seemed to be associated with the Lithium index (Li_2x) for (Zn_0.5Li_2xMg_0.5−xFe₂O₄) samples as it was observed that the E_g value has decreased with the increase of Lithium index (Li_2x) confirming that it is the reason for the bandgap shifts [1] [19] [20].

The refractive index (n): It is a dimensionless number that describes how fast light travels through the material. The refractive index (n) is the ratio between the speed of light in a vacuum to its speed in a material which does not absorb this light. The value of n was calculated using the equation Where (R) is the reflectivity. The variation of (n) vs (λ) for the five samples is shown in Figure 5. The figure depicts the relationship of the five prepared samples by Zn_0.5Li_2xMg_0.5−xFe₂O₄ refractive index (n) spectra. The maximum value of (n) is (2.159) for all samples

Figure 3. The relationship between extinction coefficient (k) and wavelengths of Zn_0.5Li_2xMg_0.5xFe₂O₄ samples.

Figure 4. The optical energy bandgap of Zn_0.5Li_2xMg_0.5−xFe₂O₄ samples.

Figure 5. The relationship between refractive index and wavelengths of Zn_0.5Li_2xMg_0.5−xFe₂O₄ samples.

at the different wavelength which is agreement with (redshift when the Lithium index (Li_2x) increased for all samples of (Zn_0.5Li_2xMg_0.5−xFe₂O₄).

Real dielectric constant (ε₁): Figure 6 shows the variation of the real dielectric constant (ε₁) with the wavelength of five samples prepared by Zn_0.5Li_2xMg_0.5−xFe₂O₄ form, which was calculated using the equation ε₁ = n² − k²; where the real the dielectric (ε₁) is the normal dielectric constant. From Figure 6; the Real Dielectric Constant (ε₁) increased in the region (340 to 432) nm for all samples of (Zn_0.5Li_2xMg_0.5−xFe₂O₄), where the absorption of the samples at these wavelengths is small, but the polarization was high. The (ε₁) reported a maximum value of (4.63) at a wavelength near 360 nm and 390 nm wavelength for the samples (Zn_0.5Mg_0.5Fe₂O₄) and (Zn_0.5Li_0.8Mg_0.1Fe₂O₄), respectively. The effect of treatment by Zn_0.5Li_2xMg_0.5−xFe₂O₄ on the (ε₁) was redshift when the Lithium index (Li_2x) increased for all samples of (Zn_0.5Li_2xMg_0.5−xFe₂O₄).

Figure 6. The relationship between real dielectric constant and wavelengths of Zn_0.5Li_2xMg_0.5−xFe₂O₄ samples.

The imaginary dielectric constant (ε₂): The imaginary dielectric constant (ε₂) vs (λ) was shown in Figure 7. This value was calculated using the equation ε₂ = 2 nK, where (ε₂) represents the absorption associated with free carriers. As shown in Figure 7; the shape of (ε₂) is as the same as (ε₁). This means that the refractive index was dominated in this behaviour. The maximum values of (ε₂) are different according to the treatment operation, so, while the maximum value of (ε₁) was (4.63) for (Zn_0.5Mg_0.5Fe₂O₄) sample at wavelength near 360 nm, the value of (ε₂) for this sample was (0.29) at the same wavelength. Similarly, the maximum value of (ε₁) was (4.63) for the (Zn_0.5Li_0.8Mg_0.1Fe₂O₄) sample at wavelength 390 nm, the value of (ε₂) was (0.34) at the same wavelength. This behaviour may be related to the different absorption mechanisms for the free carriers.

Electrical and optical conductivity: The optical conductivity is a measure of the frequency response of material when irradiated with light which is determined using the following relation,

${\delta }_{\text{opt}}=\frac{\text{αnc}}{4\text{π}}$ (1)

where (c) is the light velocity. The electrical conductivity can be estimated using the equation

${\delta }_{\text{ele}}=\frac{2{\text{λδ}}_{\text{opt}}}{\text{α}}$ (2)

The high magnitude of optical conductivity (1.34 × 10¹² sec⁻¹) following relation confirms the presence of very high photo-response of the five samples prepared by Zn_0.5Li_2xMg_0.5−xFe₂O₄ form. The increased optical conductivity at high photon energies is due to the high absorbance of the five samples prepared by Zn_0.5Li_2xMg_0.5−xFe₂O₄ form and may be due to electron excitation by photon energy as it is shown in Figure 8 and Figure 9. The maximum value of electrical conductivity is 42 (Ω∙cm)⁻¹ [21] [22] [23] [24] [25].

Figure 7. The relationship between imaginary dielectric constant and wavelengths of Zn_0.5Li_2xMg_0.5−xFe₂O₄ samples.

Figure 8. The relationship between optical conductivity and wavelengths of Zn_0.5Li_2xMg_0.5−xFe₂O₄ sample.

Figure 9. The relationship between electrical conductivity and wavelengths of Zn_0.5Li_2xMg_0.5−xFe₂O₄ samples.

4. Conclusion

Nanocrystalline, Zn_0.5Mg_0.5−xLi_2xFe₂O₄ nano ferrites (x = 0.00, 0.10, 0.20, 0.30 and 0.40) samples are successfully prepared by co-precipitation approach. UV-visible spectroscopy showed that the bandgap energy of the samples was computed to be 3.28, 3.24, 3.19, 3.15 and 3.12 eV, for Li¹⁺ concentration increased for the samples, respectively and the physical properties are increased with the lithium concentration and correspond to the Mirghni et al. study. This study was limited to the preparation and study of the composition and photometric properties. It is also recommended to study the rest of the physical and chemical properties to classify these materials and determine their applications.

Conflicts of Interest

The authors declare no conflicts of interest.

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