IHJPAS. 53 (4)2022 94 This work is licensed under a Creative Commons Attribution 4.0 International License. Investigating the Structural and Magnetic Properties of Nickel Oxide Nanoparticles Prepared by Precipitation Method Abstract This work used the deposition method to synthesize nickel oxide nanoparticles. The materials mainly used in this study were nickel sulfate hexahydrate (as a precursor) and NaOH (as a precipitant). The properties of the nanopowder were characterized by XRD, FE-SEM, EDX, and VSM. The obtained results confirmed the presence of nickel oxide nanoparticles with a face-centered cubic (FCC) structure with a lattice constant (a=4.17834 Å). Scherer and Williamson-Hall equations were used to calculate the crystallite size of about (30.5-35.5) nm. The FE-SEM images showed that the particle shape had a ball-like appearance with a uniform and homogeneous distribution and confirmed that the particles were within the nanoscale. The presence of oxygen and nickel atoms was confirmed by the EDX test. The magnetic properties results showed that nanoNiO had a narrow hysteretic loop. It consumed the least amount of energy and, therefore, can be used as a core for electric motors and transformers. Keywords: NiO nanoparticles, Williamson-Hall, XRD, Structural Properties, magnetic properties 1. Introduction The study of microscopic particles is gaining popularity due to the novel features that materials exhibit as their crystal size is reduced [1]. This is because of their wide variety of usages, such as solar cells [2], supercapacitors [3], electrochemical applications [4], and gas sensors [5]. NiO nanoparticles are among the generality of promising metal oxide nanoparticles [6]. Given the unique features of nanoscaled materials and their industrial uses, the nano-size impact of magnetism has become a powerful research topic [7]. Nickel oxide (NiO) is a promising material employed in various applications, including battery cathodes, catalysis, electrochromic films, and Doi: 10.30526/35.4.2872 Article history: Received 8 June 2022, Accepted 7 August 2022, Published in October 2022. Karrar H. Musa Department of Physics, College of Education for Pure Science (Ibn-AL-Haitham),University of Baghdad, Baghdad,Iraq. karrar.Hadi1204a@ihcoedu.uobaghdad.edu.iq Ibn Al-Haitham Journal for Pure and Applied Sciences Journal homepage: http://jih.uobaghdad.edu.iq/index.php/j/index Tagreed M. Al- Saadi Department of Physics, College of Education for Pure Science (Ibn-AL-Haitham),University of Baghdad, Baghdad,Iraq. taghreed.m.m@ihcoedu.uobaghdad.edu.iq https://creativecommons.org/licenses/by/4.0/ mailto:karrar.Hadi1204a@ihcoedu.uobaghdad.edu.iq mailto:karrar.Hadi1204a@ihcoedu.uobaghdad.edu.iq mailto:karrar.Hadi1204a@ihcoedu.uobaghdad.edu.iq mailto:karrar.Hadi1204a@ihcoedu.uobaghdad.edu.iq mailto:taghreed.m.m@ihcoedu.uobaghdad.edu.iq mailto:taghreed.m.m@ihcoedu.uobaghdad.edu.iq IHJPAS. 53 (4)2022 95 gas sensors. Bulk NiO is also antiferromagnetic, making it suitable for a wide range of magnetic applications, including pinning layers in spin valves and magnetic tunnel junctions [8]. The cubic (NaCl-type) structure of bulk NiO has a lattice parameter of 4.177 Å. It's a p-type semiconductor with wide band gap of 3.6 to 4.0 eV. Below, Neel's temperature of TN = 523 K shows antiferromagnetic ordering in the bulk form [9]. NiO nanoparticles' magnetic characteristics are susceptible to the crystal structure, size, and shape, resulting in a wide range of fascinating occurrences [10]. Nickel oxide (NiO) is one of the best metal oxides, with key qualities such as large specific capacitance, broadband gap, steady durability, and high carrier density. These characteristics are ideal for dye-synthesized solar cells, electrochromic devices, lithium-ion batteries, and other applications. Furthermore, ferromagnetism in NiO thin films at ambient temperature and its use in spintronic devices [11]. Depending on the size of the nanoparticles, nickel oxide (NiO) with a Neel temperature of 523 K shows varied magnetic characteristics such as ferromagnetism, antiferromagnetism, and superparamagnetism [12]. Nickel oxide (NiO) is a transition metal oxide with cubic crystal structure and p-type conductivity with a direct wide band gap in the range of (3.6 to 4.0) eV [8]. With the highest Neel temperature of 524K, NiO exhibits type-II antiferromagnetic (AFM) order. [13] Chemical and physical methods [14], such as the co-precipitation method [15], solvothermal [16], and sol-gel method [17], have all been used to make NiO NPs. Co-precipitation is one of the simplest techniques for producing nanoparticles among the different approaches. The co- precipitation approach lowers the temperature of the reaction by precipitating a homogenous mixture of reagents. It is a simple way to make nanopowders of metal oxides that are highly reactive in low-temperature sintering [18]. In this research, we will discuss the effect of the crystal structure and grain size on the magnetic properties of nano nickel oxide prepared by the precipitation method. 2. Experimental Method The Nickel oxide nanoparticles were prepared by the precipitation technique in the following steps: 10.541g aqueous nickel sulfate NiSO4.6H2O dissolved in 200 ml of deionized water. 3.1998 g of sodium hydroxide NaOH was dissolved in 400mL of deionized water. The mentioned solution was mixed for 30 minutes at room temperature. After that, the acidity function of the pH solution was modified by using a pH meter by adding ammonia solution NH3 drop by drop until we reached to11 and the color of the solution became blue. After that step, the solution was heated to 800 ℃ for 2 hours. The drops of dissolved sodium hydroxide were slowly added to the solution until the solution became colorless with a green precipitate. The formed precipitate was separated using filter paper with small pores and washed several times with deionized water. Finally, the precipitate was placed in an oven to dry at a temperature of 110 ℃ for 24 hours. The nano compound was placed in the electric furnace at a temperature of 450 ℃ for four hours and then left to cool down to get the nano powder of NiO. IHJPAS. 53 (4)2022 96 3. Results and Discussion 3.3. X-Ray Diffraction The XRD patterns of the produced samples clearly reveal the cubic NiO characteristic peaks at 37.3426.43.3745, 62.9490, 75.4857, and 79.4885, which correspond to crystal planes (111), (200), (220), (311), and (222) respectively. The sample's diffraction pattern corresponds to the face-centered cubic (FCC) crystalline structure of NiO, which matches the standard JCPDS card no.04-0835[19]. No impurity peaks are noticed, indicating that the NiO samples are of excellent purity as manufactured. Figure 1: X-ray diffraction pattern of NiO nanoparticles prepared by precipitation method. The software “fullprof” is used to calculate the lattice constant and theoretical density of nickel oxide nanoparticles is calculated by the following relation [20] and the result is shown in Table 1. ρ = 8 Mw N𝐴.a 3 …………………….. (1) Where, Mw: the molecular weight, N𝐴: Avogadro’s number, a: lattice constant. Crystallite size The average crystal size of the samples prepared by the precipitation method of nickel oxide nanoparticles is calculated according to Scherrer equation [21, 22]: D= 𝐾𝜆 𝛽𝑐𝑜𝑠𝜃 By adding the term ε = 𝛽𝑆 𝑡𝑎𝑛𝜃 ,which represents the micro strain to the Scherrer equation, the equation becomes in the following form and is called the Williamson-Hall equation [23,24]: 𝛽ℎ𝑘𝑙 = 𝛽𝑠 + 𝛽𝐷 ………………… (2) 𝛽ℎ𝑘𝑙 = 𝑘𝜆 𝐷𝑐𝑜𝑠𝜃 + 4ε𝑡𝑎𝑛𝜃 ………………… (3) 𝛽ℎ𝑘𝑙 𝑐𝑜𝑠𝜃 = 𝑘𝜆 𝐷 + 4ε𝑠𝑖𝑛𝜃 ……………….(4) D: crystal size (nm). K: shape factor. λ: the wavelength of X-rays. βhkl: maximum width at mid intensity (FWHM). θ: the angle of incidence of X-rays (Bragg angle). ε :micro strain. The results are shown in Figure 2 and Table 1. 0 500 1000 1500 2000 2500 20 30 40 50 60 70 80 In te n si ty ( a .u .) 2 Theta (deg.) IHJPAS. 53 (4)2022 97 Figure 2: Plot of W-H analysis of NiO nanoparticles prepared by precipitation method. It is a property of the material and has great importance, as it is possible to know the properties and type of the material from this value, as the smaller the size of the nanoparticles, the larger the surface area. The surface area is calculated in the following relationship [25.]: SA=6000/D ρ …………………………… (5) SA: surface area (m2/g). D: particle size (nm). ρ: the density of the material (g/cm3). The results are shown in Table 1. Crystallization Factor It is one of the important indicators by which it is possible to know if the sample is monocrystalline or polycrystalline based on X-ray diffraction data. It is calculated according to the following relationship [26, 27]: Icry = D(AFM,SEM) DXRD ……………………………. (6) Icry: Crystallization coefficient. D: crystal size from AFM scan or SEM. D XRD: crystal size using Scherer equation. If the value of the crystallization coefficient is equal to one, then the crystal is monocrystalline, but if its value is greater than one, then the substance is polycrystalline [28]. The results are as shown in Table 1. Table 1: Some of structural parameters of NiO nanoparticles prepared by precipitation method. a (Å) 𝜌 (g/cm3) DSH (nm) DW-H (nm) Micro Strain H-WSA )/g2m( SHSA )/g2m( Icr 4.17834 6.80112 30.5 35.5 4x10-4 24.82 28.96 1.82 The “Powdercell” software was used to calculate the length of the ionic bond between the two atoms of oxygen and nickel in the crystal lattice. The results were included in Table (2). The angles between them were calculated, and the results were included in Table (3). Table 2: The length of bonds between Ni-O nanoparticles prepared by precipitation method. Bond number Bond length (Å) atom2 atom1 2 2.9543 O Ni 2 2.9873 Ni O 1 4.2069 O O y = 0.0004x + 0.0039 0.0025 0.003 0.0035 0.004 0.0045 0.005 0.0055 0.006 1 1.5 2 2.5 3 β c o sθ 4sinθ IHJPAS. 53 (4)2022 98 Table 3: The angles between Ni-O nanoparticles prepared by precipitation method. 3.2. Texture Coefficient It is a description and measure of the degree of the best orientation ratio between crystalline planes and can be calculated using the Harris method according to the following equation [29]: TCℎ𝑘𝑙 = Iℎ𝑘𝑙/I°ℎ𝑘𝑙 1 N ∑ Iℎ𝑘𝑙/I°ℎ𝑘𝑙N …… ………………….. (7) N: the number of apparent peaks in the X-ray diffraction pattern. Ihkl: the measured relative intensity. Io : the standard intensity of the plane (hkl) from the (JCPDS) card[29]. It can be noticed from the obtained values that there is the highest and best growth of nanoparticles for the samples prepared along the planes (311) and (200). Due to its high formation energy, the lack of growth is at other planes, and the lowest growth is at the plane (111). In general, if TC≅1, then this indicates that the planes' crystal growth is in random directions. This is in good agreement with the JCPDC index [30], but if TC>1 indicates a preferred orientation, and if TC<1, it is polycrystalline, meaning there is a lack of growth Crystal surfaces [31,32], and the results are shown in Table 4. Table 4: The value of angles between Ni-O nanoparticles prepared by precipitation method. TC 222)) TC (311) TC (220) TC (200) TC (111) 0.79 1.01 0.83 1.16 0.77 3.3. Dislocation Density Dislocations that occur in the structure of the crystal strongly affect the properties of the material and represent the number of dislocation lines per unit volume of the crystal, and the dislocation density can be calculated according to the following equation [33]: δ = 15βhkl cosθ 4𝑎𝐷 ………………………………………. (8) δ: intensity of dislocations. D: crystal size (nm). a : lattice constant (Å). βhkl: maximum width at mid intensity (FWHM). θ: the angle of incidence of X-rays (Bragg angle). Crystal defects are formed during the crystal growth process, and it is difficult to get rid of impurities and defects in the crystal, and the presence of defects is sometimes an advantage. Among those crystals, defects are dislocations; the dislocation density of samples is calculated for each plane and the results are shown in Table (5). Angle number Angle atom2 atom2 atom1 2 172.0 Ni O Ni 1 82.91 O O Ni 1 85.90 O Ni O IHJPAS. 53 (4)2022 99 Table 5: The Dislocation Density ofNi-O nanoparticles prepared by precipitation method. 3.4. Magnetic Properties A vibrating-sample magnetometer (VSM) was used to measure the magnetic characteristics. Because of the odd electron present, nitric oxide has a paramagnetic property (unpaired electron). When this electron is lost, the diamagnetic NO+ is created. The relationship between the magnetic flux (B) and the intensity of the applied magnetic field (H) is one of any magnetic material's most important magnetic properties. It is represented by the hysterical loop (B-H loop), which is a measure of the energy lost per unit volume during one magnetization cycle. The chemical composition affects the shape and width of the hysterical loops. Figure (3) shows the magnetization curves of the NiO nanoparticles for the sample prepared by the deposition method. We notice that the hysterical loop is narrow. From Table (6), it is noted that the highest saturation is 0.085 emu/g. Furthermore, the samples having the least area for the retardation ring means that they consume the least energy and, therefore, can be used as cores for electric motors and transformers because they have the lowest magnetic loss [34]. The large surface area compared to the volume of nanomaterials, interfaces, defects, and oxygen vacancies make the magnetic properties of nanoscaleNiO very complex [35]. In addition, it was found that NiO nanoparticles' magnetic characteristics are strongly influenced by particle size [36]. Figure 3: magnetization versus magnetic field ofNi-O nanoparticles prepared by precipitation method. Table 6: values of magnetic properties ((Hc, Hs, µs) ofNi-O nanoparticles prepared by precipitation method. -0.01 -0.005 0 0.005 0.01 -10000 -5000 0 5000 10000 M a g n e ti c M o m e n t (e m u /g r) Magnetic Field (Gauss) δ (222) *10 14 (m-2) δ (311) *10 14 (m-2) δ (220)*10 14 (m-2) δ (200) *10 14 (m-2) δ (111) *10 14 (m-2) 21.732 17.876 6.236 14,647 15.715 µs (emu/g) Hs (Oe) Hc (Oe) 0.085 8000 -100 IHJPAS. 53 (4)2022 100 3.5. Field Emission-Scanning electron microscope (FE-SEM) analysis The scanning electron microscope (SEM) technique is used to photograph the samples for the purpose of knowing the details of the sample's surfaces and knowing the shape, size, and degree of homogeneity of the samples. SEM images are magnified at 135 kX, and Figure 4 shows the morphology and average particle size present in the samples of NiO NPs prepared by the deposition method. The SEM image shows that the particle shape has a ball-like appearance with a uniform and homogeneous distribution. Figure 4: SEM micrographs of nickel oxide nanoparticles. 3.6. Energy Dispersive X-ray (EDX) The elements of the prepared nanoparticles can be identified using EDX spectroscopy, which measures the energy difference between the two outer shells and the element's atomic structure. The EDX spectrum of NiO NPs shows the peaks corresponding to Ni and O, as shown in Figure 5. The reason for the presence of C is the residue of the combustion reaction, and the presence of Pt is one of the characteristics of the device, as the sample is coated with a layer of Pt to increase the conductivity [37]. In addition, the appearance of sulfur S as an impurity in the sample is very small percentage due to the use of nickel sulfate as raw materials in the deposition method. The peaks of the nickel element appear with three energies at (Kα, Lα) and its quantity Kα = 7.480 keV, Lα = 0.849 keV, and the peak of the oxygen element is shown at the site Kα = 0.525 keV. Figure 5: EDX spectroscopy of nickel oxide nanoparticles. IHJPAS. 53 (4)2022 101 4. Conclusion The nickel oxide (NiO) nanoparticles were prepared in a low-cost method by precipitation technique. The aqueous nickel sulfate NiSO4.6H2O and NaOH were used as precursors. 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