## 3.1 XRD Analysis

As illustrated in Fig. 1, the samples' X-ray diffraction patterns display the characteristic peaks of Co-doped La2CuO4 materials. The 2*θ* peaks from the planes disclose the orthorhombic structure of the synthesised materials with space group *Bmab* (JCPDS No. 88–0940). The diffraction peaks at 2*θ* values around 24.24˚, 27.08˚, 30.95˚, 33.02˚, 33.44˚, 41.05˚, 41.63˚, 43.35˚, 47.74˚, 53.85˚, 54.30˚, 55.70˚, 58.05˚, 64.76˚, 65.08˚, 69.64˚, 69.90˚, 75.23˚, 76.51˚ and 78.35˚ the crystallographic planes are mapped to 111, 004, 113, 020, 200, 006, 115, 204, 220, 206, 117, 224, 133, 226, 135, 040, 400, 317, 228 and 333 crystallographic planes respectively.

However, doping with Co2+ resulted in a distinct trend. It was discovered that Co2+ doping causes the formation of a new secondary La2O3 phase. Cu2+ ions are replaced by Co2+ ions, resulting in the development of two phase systems: orthorhombic (La2CuO4) and hexagonal (La2O3, space group *P-3m1*). The strength of the peaks associated with the hexagonal phase steadily increases with increasing Co2+ content. As the Co2+ doping concentration increased, this effect became more apparent, confirming the creation of a stable two-phase perovskite system [19–23].

The formula was used to calculate lattice parameters based on the characteristic plane reflections and their related placements.

\(\frac{1}{{{d^2}}}=\frac{{{h^2}}}{{{a^2}}}+\frac{{{k^2}}}{{{b^2}}}+\frac{{{l^2}}}{{{c^2}}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,.....(1)\)

The inter-planer spacing, or dhkl, is determined by Eq. (1). It is associated with the Miller indices h, k, and l, whereas the lattice parameter, or a, is represented by k. The estimated values for the dhkl spacing, and lattice constant (a, b and c) are displayed in Table 2. For La2CuO4, the computed lattice constant values (a = 5.361Å) are in good agreement with the previously published values (a = 5.3556Å) [23]. In contrast, as the dopant (x) value increases to 5.349 Å, the lattice constant increases as well. The reason for this discrepancy is that the ionic radiuses of Cu2+ radius = 0.60Å and Co2+ radius = 0.72Å are different. Debye Scherer's formula [24], which is provided in Eq. (2), was used to get the average crystallite size (D).

\(D=\frac{{0.89\lambda }}{{\beta \cos \theta }}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(2)\)

Where, β is the diffraction peak's full width at half maximum (FWHM), 2θ is the diffraction angle, and λ is the X-ray source's wavelength. When comparing the crystallite size (D) 28, 32, 36 and 41 nm of all the Co2+ doped La2CuO4 to that of pure La2CuO4 nanoparticles.