## 3 Results and Discussion  
XRD is a powerful technique that is extensively used to study the crystal structure, lattice parameters, crystallite size, dislocation density as well as crystal strain. The development of a particular crystalline phase was critically governed by the calcination process. Figure 2 shows the XRD pattern of CeO\({}_{2}\)/NiO nanocomposite in the 20 range of 20-75 degrees. The diffracted peaks appearing at 20 values of 28.7\({}^{\circ}\) and 47.4\({}^{\circ}\) were indexed as (111) and (220) and matched with the ICSD ref. no. 00-001-0800 which confirmed the presence of CeO\({}_{2}\) while peaks appearing at 33.1\({}^{\circ}\), 56.4\({}^{\circ}\), 62.3\({}^{\circ}\), and 69.8\({}^{\circ}\) were indexed as (200), (311), (103), and (440) and matched with ICSD ref. no. 01-073-1519 which confirmed the presence of the NiO phase having an FCC structure [22]. Since there was no peak other than CeO\({}_{2}\) and NiO, it confirmed the formation of CeO\({}_{2}\)/NiO nanocomposite. For CeO\({}_{2}\), the most intense peak was (111) and for NiO, it was (200). Using [PERSON]'s formula, the crystallite size was calculated from the most intense peaks. The calculated crystallite size was \(\sim\)10 nm for CeO\({}_{2}\) and 15 nm for NiO. Figure 3 shows the SEM images of CeO\({}_{2}\)/NiO nanocomposite at (a) 4000 and 50,000 magnifications from where we can analyze the morphology, particle size distribution, and surface texture. The image at low magnification (Figure 3a) covered more area and thus provided useful information regarding particle distribution which was uniform throughout the surface. When magnification was increased (Figure 3b), it provided more chance to look into the minor details and thus revealed a cauliflower's leaf-like morphology. This kind of morphology exposed high surface area and thus had high potential as an electrode material for energy storage devices like supercapacitors [23]. Figure 2: Indexed XRD pattern of CeO\({}_{2}\)/NiO nanocomposite. To check the elemental composition of the prepared sample, EDX analysis was performed at a fixed area of SEM images as shown in Figure 4. The purity of the sample could be verified from the EDX spectra because there were only peaks of Ce, Ni, and O in the graph with wt. % of 44.80, 23.08, and 25.84, respectively. In addition, a peak of C was also there in the low energy region which came from the environment. The weight percentages of all these elements were provided in the tabular form as an inset. In order to reveal the minor details of morphology and crystal geometry, the HR-TEM images were captured as shown in Figure 5. Figure 5a,b revealed the polycrystalline nature of this nanocomposite with the interplanar spacing of 0.155 nm. Some of these crystallites were grown in bipyramid shape as highlighted by sketching its schematic. The presence of concentric circles shown in the SEAD pattern supported the polycrystalline nature (Figure 5c). Here, the estimated value of crystallite size was in good agreement with the XRD results [24]. Figure 4: **(a)** SEM image of CeO\({}_{2}\)/NiO nanocomposite with scan area and **(b)** Energy-dispersive X-ray spectroscopy (EDX) spectrum with a weight percentage of all elements. Figure 3: SEM images of CeO\({}_{2}\)/NiO nanocomposite at **(a)** 4000\(\times\) and **(b)** 50,000\(\times\). FTIR spectrum of CeO\({}_{2}\)/NiO nanocomposite in the range of 400-4400 cm\({}^{-1}\) is shown in Figure 6. Here we observed multiple peaks corresponding to bond stretching and bond vibrations of metal oxides. A significant peak centered at 404 cm\({}^{-1}\) the characteristic peak corresponding to the stretching vibration of the Ni-O bond in NiO present in this nanocomposite [25]. The same kind of observation was made by [PERSON] and [PERSON] at a slightly higher wave number i.e., 443 cm\({}^{-1}\)[26]. The adjacent peak centered at 541 cm\({}^{-1}\) which was attributed to the characteristic stretching of the Ce-O bond and thus confirmed the presence of CeO\({}_{2}\)[27].