Essay Example on Reduction in Ni concentration inside the YBCO lattice.










The X-ray diffraction patterns for all composite samples of 100 x YBa2Cu3O7 δ x Ni where x 0 1 2 5 5 7 5 10 15 wt were analyzed and shown in Figure 2 a. From it one can easily see a predominant phase perovskite structure YBCO with orthorhombic Pmmm symmetry. Growing peaks of NiO monoclinic phase with unobservable impurity peaks are founded as well The intensities at 001 200 and 111 planes of NiO increase gradually with an increase of the addition of Ni, In other words, more numbers of diffraction is coming from the displayed planes as shown in Figure 2 b. This indicates the agglomerations or segregations of large quantities of Ni in the form of NiO into patches or dots. The lattice parameters a b and c were calculated using the least square method through d value and hkl planes for orthorhombic unit cell structure and tabulated in Table 1. The analysis of the XRD data indicates the presence of orthorhombic peaks of YBCO in all composites samples with different lattice constants. From the data one can observe the distortions in the orthorhombic unit cell of YBCO.

 The addition of Ni produces different YBCO crystallites in the same sample i.e different orthorhombic phases of different unit lattice volumes and different c a distortion are presented. This is due to the different doping levels of Ni ions in the YBCO matrix in each sample. In other words, highly Ni-doped YBCO traces of the diminishing c ratios are sticking to NiO patches. Whereas the YBCO of lower Ni2 doping is in the middle region between the two NiO patches. The increase of the number of Ni2 ions in Cu plane sites which due to an increase of Ni addition from 2 5 up to 7 5 gives rise to steady decrement in c a ratios, On the other hand, more Ni wt namely 10 and then 15 wt gives rise again to increased c a ratios relative to 7 5 wt sample. The SEM images were done to characterize the microstructure of pure YBCO and some of the prepared samples as shown in Figure 3. From SEM images two distinct features are observed one for all samples which exhibit randomly oriented grain sizes in all directions with the presence of pores between them. The second one is the segregation of NiO in patches. It can be also seen that EDX analysis for the positions X1 to X4 shows all the compositional elements in proper stoichiometric amount. For more inspection of Figure 3 and Table, 1 one can easily explain how NiO patches affect the level of Ni doping on the YBCO matrix that definitely confirms the above results. Furthermore, the presence of NiO in forms of patches gives different concentrations of Ni 2 ions inside the lattice of YBCO. In other words, YBCO crystallites close to NiO patches contain a high concentration of Ni 2 ions whereas YBCO crystallites far from NiO patches contain a lower concentration of Ni 2 ions. Figure 3 X1 gives the EDAX analysis of position X1 that shown in Figure 3 an in which proves the elemental composition of pure YBCO. Whilst Figures 3 X2 X3 supply the EDAX analysis of positions X2 and X3 that shown in Figure 3 b. This verifies the high concentration of Ni in the blackish patch and the decrease in Ni concentration out of the patch. Figure 3 X4 shows the linear EDAX analysis of the line shown in Figure 3 d. This proves the reduction in Ni concentration inside the YBCO lattice when moving away from the blackish patch.

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