Figure 1 shows the XRD pattern of the sample that is prepared with BaCO₃

(marked by A) and Ba(OH)₂∙8H₂O (marked by B) respectively. At intervals of 20˚ - 60˚, it appears that both spectra show the same pattern of diffraction spectra. Figure 1 has been shown the major peaks of the Nd₁Ba₂Cu₃O_7−δ phase, i.e. the peaks of the diffraction plane (013) and (103) are occurred at an angle of 2θ between 32˚ - 32.8˚, the diffraction of planes (020) and (200) are occurred at an angle of 2θ between 46˚ - 47.3˚, and the diffraction of planes (123) and (213) are occurred at an angle of 2θ between 57.5˚ - 58.5˚ [3] [4] [9] . Search-match by using Match 3.6.1 software with entry number 96-154-0949 (formula Nd₁Ba₂Cu₃O_6.57) the volume fraction that of both sample are almost the same, i.e. 84% obtained. However, the diffraction peaks of sample B appear sharper and their intensity is higher than the same peaks in sample A. For example, peak of 103 at 2θ = 32.36, sample B have FWHM = 0.10 and intensity = 1926 counts, meanwhile same peak from sample A have FWHM = 0.16 and intensity = 1854 counts.

It has been conducted refinement to XRD data with Rietveld analysis method by using Rietica software with ICSD Collection Code 78453 as a reference, and was obtained data as shown in Table 1 and Table 2. From value of Goodness of Fit (GofF) as formulated in [10] and from Table 1 was obtained the GofF i.e. 1.8891 and 1.7023 respectively for sample A and sample B. The refinement result is said to be good if GofF < 2 [10] therefore, sample A and B have a good match between the experiment and the expected results. It appears to that sample B has a smaller GofF than sample A. Table 2 shows that the lattice parameter values of a, b and c for sample B are slightly larger than of sample A. It also appears that the equivalent to particle size of the sample B is greater than of the sample A. It is indicates that the crystallization in the sample B is better than in the sample A.

Figure 2 shows the grouping of the peaks of the diffraction pattern based on the diffraction planes. The diffraction planes of (013) and (103), (006), (020) and (200), (123) and (213) are located at the 2θ angle intervals of 32.0˚ - 32.8˚, 45.7˚ - 47.0˚, and 57.0˚ - 58.5˚ respectively. The peaks of diffraction patterns on each diffraction plane are separated by the very small 2θ angle. These indirectly imply that the Nd₁Ba₂Cu₃O_7−δ phase formed on the samples A and B their structure are tends to in tetragonal symmetry [11] [12] .

Figure 2 also shows there is the plane splitting and the 2θ angular shift toward a smaller 2θ angle on the XRD peaks pattern of sample B, these indicate there to the difference of the lattice parameter value of Nd₁Ba₂Cu₃O_7−δ phase on the both samples as shown in Table 2. In this case the c-lattice parameter of sample B is greater than that of A. As it is well known that the structure of the Nd₁Ba₂Cu₃O_7−δ phase can be in tetragonal or orthorhombic symmetry, it depends on the oxygen content. In the Nd₁Ba₂Cu₃O_7−δ, lattice parameter c depends on the oxygen content y = 7 − δ with 0 ≤ δ ≤ 1 [4] [7] . The linear relationship between the lattice parameters c and the oxygen content for the Nd₁Ba₂Cu₃O_y phase as in [13] ,

It can be seen that the c-lattice parameter value is increase with the decreasing of oxygen content y. If the oxygen content is calculated by using equation (3) and from the lattice parameter c in Table 2 was obtained the oxygen content of the samples A and B are y = 6.46 and y = 6.38 respectively. It was found that the Nd₁Ba₂Cu₃O_7−δ phase formed on samples A and B has different oxygen content with oxygen-deficient δ = 0.54 and δ = 0.62 respectively. The lattice parameters of a, b and c with a » b < c/3 as shown in Table 2, and the c/3 value of samples A and B are 3.9206 Å and 3.9275 Å respectively. These conditions indicate that both samples are in the Nd₁Ba₂Cu₃O_7−δ phase formed on samples A and B has tetragonal symmetry [3] [14] .

The orthorhombic splitting (OS) unit cell as in [9] , i.e.

From Table 2, were obtained the value of OS = 7.7 × 10⁻⁴ and 1.9 × 10⁻⁴ for samples A and sample B respectively. It was found the value of OS is very small, that gives a hint that the Nd₁Ba₂Cu₃O_7−δ phase formed on sample A and B have a small that orthorhombicity.

Therefore, the symmetry of the Nd₁Ba₂Cu₃O_7−δ phase on both the sample are tends to be tetragonal. This corresponds to the amount of which oxygen content in the cell unit less that than to 6.55, oxygen-deficient δ > 0.45 [2] [7] .

It has been made a model of the lattice structure (cell unit) for both samples by using Diamon 4.4.0 software and the refinement result, it is shown in Figure 3. The legend of the Figure 3 corresponds to the legend of the figure that has made as in [14] . It was found that the structure of the Nd₁Ba₂Cu₃O_7−δ phase that formed on the sample A and B are similar.

The structure of Nd₁Ba₂Cu₃O_7−δ that has been produced in this study are agree to the structure of Y₁Ba₂Cu₃O_7−δ [15] [16] . The crystal structure is characterized by the arrangement of copper-oxygen planes and copper-oxygen chains: CuO layer where in the a-c plane, Cu(1) copper is surrounded by four oxygen ions (CuO₄) and it forms a chain along the b-axis. Two layers of CuO₂ where the Cu(2) is surrounded by five oxygen ions, it forms a polyhedron. Both layers of CuO₂ are separated by an Nd atom.

Figure 3 shows that Ba atom was positioned above and below of the cell unit, while the position of an Nd atom is at it’s a center. Nd and Ba atom are piled along the c-axis in the sequence of Ba-Nd-Ba. The position of Nd atom is lies between of the two CuO₂ plane and the Ba atom lies between CuO₂ planes and

CuO₄ chains. In the layered structure, the stacking sequence of layers along the c-axis of the cell unit as follows BaO-CuO-BaO-CuO₂-Nd-CuO₂-BaO-CuO-BaO [17] .