Morphological and optical investigations of the NiZnFe2O3 quaternary alloy nanostructures for potential application in optoelectronics

Nanostructure such as quaternary alloy offers an unprecedented opportunity for alloy composition control in a wide range, unavailable with traditional epitaxial film materials. The technique of chemical co-precipitation has been employed to synthesize the NiZnFe2O3 quaternary alloy nanostructure, which is cost-effective and friendly environmentally. The study of morphology for the mentioned NiZnFe2O3 quaternary alloy nanostructure is elaborated by scanning electron microscopy (SEM) to measure the grain size. The optical properties are investigated via UV-visible spectrophotometry (UV-vis) and Fourier-transform infrared spectroscopy (FTIR) to research the absorption, transmission, reflection and bandgap for the mentioned NiZnFe2O3 quaternary alloy nanostructure, also, for verifying optical dielectric constant and refractive index models using specific empirical models. The grains size and energy gap are investigated to recommend the suitability results for NiZnFe2O3 quaternary alloy nanostructure. Finally, Ravindra et al. models are an appropriate for potential application in optoelectronics.


Introduction
Quaternary alloys have the potential for optoelectronic applications, and they are crystallized usually as tetragonal or cubic structures [1,2]. The industry of optoelectronics has grown rapidly during the last decades [3], and 80-90% of the solar cell technology is dominated by silicon-based materials that is proved to be a solid technology in the PV modules, due to cost-effectiveness and abundance of the used silicon in bulk (first generation), thin film (second generation) and some of the nanostructured (third generation) solar cells [4]. Advancements in the area of concentrating photovoltaics (CPVs) give best solar energy-to-electricity conversion efficiency [5], and also other investigations in perovskite photovoltaics reveal the exceptional light-absorbing properties exhibited by organometallic halides, which are chemical compounds that contain bonds between organic compounds and metal [6].
Ceramic-based quaternary II−VI materials are popular due to their high characteristics of structure and applicability for optoelectronics and others [7]. The NiZnFe 2 O 3 quaternary alloy nanostructure com-prises tetrahedral materials of chalcopyrite structure optoelectronics. Other ternary [8], quaternary [9] and quinternary [10,11] alloys have been researched. The bandgap of 2.5 eV is direct with non-toxic and abundant elements [12]. It is very important that the size and shape of nanostructure may affect the function and performance of optoelectronics. Specific methods have explored quaternary alloys and effective techniques have been utilized to prepare the alloys such as solvothermal [13], radio-frequency magnetron sputtering [14], sequential electrodeposition [15], ultrasonic spray pyrolysis [16] and electrosynthesis [17]. The spin coating technique shows a direct correlation between high annealing temperature and crystallite size [1]. The NiZnFe 2 O 3 quaternary alloy nanostructure has been synthesized by the chemical co-precipitation technique. The optical characteristics complement extravagantly for the interface studies. Many techniques, such as absorption, reflection, transmission and absorption coefficient permit in situ applications, and if applied in the FTIR, show quantitative information on an analytical and application level [17].
The photocatalytic and fluorescence sensing applications of manganese-doped zinc oxide nanostructures, synthesized by the solution combustion technique, using zinc nitrate as an oxidizer and urea as a fuel, are reported. The synthesized Mn-doped ZnO nanostructures have been analysed in terms of their surface morphology, phase composition, elemental analysis and optical properties [18]. But, Ag/AgVO 3 @CdS/BiVO 4 heterostructure photocatalysts, by the photoreduction strategy and tested for H 2 evolution under artificial solar irradiation, were synthesized by Mandari et al. [19]. The effects of Ag/AgVO 3 @CdS/BiVO 4 heterostructure on the crystal phase, visible absorption, morphology, strong interactions and charge carrier separations were analysed by a series of characterization techniques. Based on the photocatalytic test, 1Ag/AgVO 3 @CdS/BiVO 4 exhibited highest solar light-driven activity for hydrogen production (105,541 μmol/g) and with an apparent quantum yield. And, Ni 100−x Fe x alloy catalysts are an alternative to Pt-based catalysts for the hydrogen evolution reaction (HER) in water electrolysis [20]. For optimum bonding and adhesion stability between a carbon paper (CP) electrode and Ni 100−x Fe x alloy particles, the latter (obtained by varying the Ni/Fe ratio) is directly grown onto the CP electrode hydrothermally. The shape, crystallinity, and electrochemical properties of the alloy particles were analysed using scanning electron microscopy, transmission electron microscopy, Xray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and linear sweep voltammetry (LSV).
Single-phase equi-atomic (Al0.2Co0.2Fe0.2Mn0. 2Ni0.2) 3 O 4 high-entropy oxide (HEO), having spinel structure, is synthesized using simple and cost-effective microwave-assisted co-precipitation technique [21], followed by calcination at 500°C. The material obtained is highly crystalline and stable at higher temperatures. Co-precipitation is most frequently applied to prepare Layered Double Hydroxides (LDHs). Two variations of this method can be used, depending on the pH control conditions during the precipitation step. In one case, the pH values vary, while in the other, they are constant. Although research groups have their preferences, no systematic comparison of the two variations of the coprecipitation method is available in the literature [22]. The calculated optical energy band gaps, obtained by Tauc's relation from UV-vis absorption spectra, where the optical properties of absorbance, reflectance and transmittance are investigated for the best optical quality and potential application in optoelectronics [23][24][25][26][27][28][29][30][31].
The NiZnFe 2 O 3 quaternary alloy nanostructure is highly popular due to its optical and morphological properties. To the best of our knowledge, there are no available studies in the literature for the mentioned quaternary alloy nanostructure. The bandgap of 2.5 eV at ambient temperature is utilized for potential applications as optoelectronics. In this work, the chemical coprecipitation technique has been prepared to synthesize NiZnFe 2 O 3 quaternary alloy nanostructure because it's cost-effective and environment-friendly. The optical and morphological properties are investigated. The scanning electron microscope (SEM) has been used to show the morphology studies that are homogenous and dense grains [32]. The UV-visible spectrophotometry (UV-vis) has been used to detail the optical studies of absorbance, reflectance, transmittance, bandgap and Fourier-transform infrared spectroscopy (FTIR) path the way for a successful potential application in optoelectronics.

Experimental procedure
The green approach for synthesizing nanoparticles is always better due to eco-friendliness [33]. All solvents and chemicals are obtained from Sigma-Aldrich (USA, http://www.sigmaaldrich.com). The solutions of aqueous salt for nickel nitrate, cobalt nitrate, magnesium nitrate, zinc nitrate or (CH 3 COO) 2 .Zn.2H 2 O) and ferric nitrate (Fe(NO 3 ) 3 .9H 2 O) are in molar ratio 1:1:2 to reach the optimum synthesized materials. For the detailed green synthesis process, the chemical co-precipitation approach has been carried out. Under constant stirring, the solution is cooled to room temperature. The obtained material is NiZnFe 2 O 3 quaternary alloy nanoparticle used for further analysis and characterization. The process is as follows: The first step is to dissolve 1 gram of dried Gujarat, which is a short-sized plant herb with soft, green, delicate stem without woody tissues, in 100 ml of distilled water for 30 min, followed by dissolving zinc nitrate of molecular weight of 189.39 in distilled water for 30 min. and 60°C using [34] where W is the weight, equal to 18.939 m, and V is the volume. The two solutions are mixed via a stirrer for 30 min. to obtain the nanocomposite. The second step is to dissolve 1 g of dried Gujarat in 100 ml of distilled water for 30 min., followed by dissolving iron nitrate of molecular weight of 24.86 in distilled water for 30 min. and 60°C using equation (1). The two solutions are mixed via a stirrer for 30 min. to obtain the nanocomposite. The nickel nitrate of molecular weight of 241.86 is dissolved separately and mixed with dissolved Gujarat plant to get thawing and nanocomposite.
The last three solutions are added to the first and second steps mentioned upon to synthesize the quaternary alloy nanostructure. The optical properties are measured at room temperature using ultraviolet- visible spectrophotometry (UV-vis; Lambda 950, Perkin Elmer, USA). Surface morphology and grain size are investigated by a scanning electron microscope (SEM JSM-6010LV, USA). Fourier transform infrared spectroscopy (FTIR) (perkinelmer, NIRFlex N-500, Switzerland) in the region 4000-500 cm −1 is to study the composition and quality of NiZnFe 2 O 3 quaternary alloy nanostructure.

Morphological study
Scanning electron microscopy (SEM) images of the NiZnFe 2 O 3 quaternary alloy nanostructure are shown in Figure 1. The NiZnFe 2 O 3 morphology presents agglomerated grains and small cubes. The formation of crystallites is dense for the NiZnFe 2 O 3 quaternary alloy nanostructure. Figure 1 shows agglomerated particles and good and large nanostructures adhere to the surface due to the material content, the analogy is clear. The homogeneity of cube-like nanostructure is illustrated in NiZnFe 2 O 3 image that reflects the crystallite size. The grain size is measured, as given in Table 1.

Optical properties
The optical studies are very important for the potential application in optoelectronics to illustrate the necessity of absorption, transmission, reflection, absorption coefficient and FTIR from analytical viewpoint.

Absorbance
The absorbance spectra of the NiZnFe 2 O 3 quaternary alloy nanostructure are measured at ambient temperature via UV-vis in wavelength range of 350-1150 nm, as shown in Figure 2. The absorbance spectra are due to material behaviour. The correlation between absorption and wavelength is inverse.

Transmittance
The transmittance spectra are shown in Figure 2 of the NiZnFe 2 O 3 quaternary alloy nanostructure in the wavelength range of 350-1150 nm. The transmittance is due to the inverse correlation with absorbance. The correlation between transmittance and wavelength is direct. The highest transmittance is below 1 a.u. NiZnFe 2 O 3 quaternary alloy nanostructure.

Reflectance
The reflectance spectra are illustrated in Figure 2 for the NiZnFe 2 O 3 quaternary alloy nanostructure in the wavelength range of 350-1150 nm. The increase of reflectance is due to the direct correlation with transmittance. The overview correlation between reflectance and wavelength is inverse. The highest reflectance is almost 0.2 a.u. at the NiZnFe 2 O 3 quaternary alloy nanostructure.

Absorption coefficient
The absorption coefficient value is high for short wavelength, then begins to decline as the wavelength increases for the area between 350 and 390 nm of energy gap (E g ), as illustrated in Figure 3. This is meaning the photons absorption is direct, while the absorption breadth mentions to varied types of absorption, direct and indirect that are arisen of crystal structure changing correspond to different atomic numbers. The edge of absorption shifts towards ultraviolet as the atomic number increases. For the NiZnFe 2 O 3 quaternary alloy nanostructure, the absorption edge is at 393 nm (E g = 3.15 eV), as given in Table 1. The energy gap (E g ) of the NiZnFe 2 O 3 quaternary alloy nanostructure is determined via direct transition between the valance and conduction bands. The edge of absorption follows the exponential law. The absorption coefficient obeys [11].
where constant refers to A, bandgap refers to E g , and 1/2 refers to n, as illustrated in Figure 3.   The difference in E g is due to parameters, such as the precursors' nature and concentration, granular structure, crystal structure and structural defects as well as differences in grain boundaries and imperfections in polycrystallines [11]. The physical factor of refractive index n is important. From theory viewpoint, n is related to local polarizability and density [35]. Different relationships of n and E g have been reported [36][37][38][39][40][41][42][43] to validate our current work. Ravindra et al. [35] have presented a direct correlation between high-frequency refractive index and E g : α = 4.048 and − β = 0.62 eV −1 . But, Herve and Vandamme [36] have suggested another relation as n = 1 + A Eg +B 2 (4) A = 13.6 eV and B = 3.4 eV. And, Ghosh et al. [37] had considered another approach of Penn [44] and Van Vechten [45]. A is contributed from valence electrons and B is added to E g to present the following: A = 25E g + 212, B = 0.21E g + 4.25 and (E g + B). Therefore, the mentioned models of n and E g are researched.
Also, the optical dielectric constant ( ∞ ) is obtained via ∞ = n 2 [45]. The calculated n and ∞ are displayed in Table 1. This proves that the Ravindra et al. model is an appropriate for the potential application of optoelectronics.

FTIR
To investigate the chemical interaction of the NiZnFe 2 O 3 quaternary alloy nanostructure, the Fouriertransform infrared spectroscopy (FTIR) analysis is achieved in the range of 400-4000 cm −1 , as shown in Figure 4 corresponding to the stretching vibrations. FTIR and its corresponding data are recoded. It is obtained for the NiZnFe 2 O 3 quaternary alloy nanostructure, as demonstrated in Figure 4.  1743.65 cm −1 of stretching of C-C. A medium strong in 1635.64 cm −1 is due to stretching vibrations [46]. The stretching vibration mode originates from the reaction intermediates or residues of acetates used for the preparation of the mentioned alloys. The broad absorption band might be due to the stretching mode to confirm that ions are introduced in the sites. The electrochemical contribution is important for different technological applications. The optoelectronic devices are important in energy storage to enable renewable energy conversion technologies for giving a direct relationship between electricity generations and associated chemical changes in a reaction.

Conclusions
The NiZnFe 2 O 3 quaternary alloy nanostructure was synthesized using chemical the co-precipitation technique. Improvement in morphological studies toward homogenous-formed nanograins was noted. The grain size was 44.80 nm. Furthermore, the bandgap was 3.15 eV. The spectra of absorption were lowest meaning that the transmission and reflection were highest. Ravindra et al. model was recommended for potential applications in optoelectronics. The FTIR results were obtained and clusters' mean size has recommended the NiZnFe 2 O 3 quaternary alloy nanostructure for appropriate band of weak absorption, very weak vibration and medium strong due to stretching vibrations.