115 © 2025 The Author(s). Published by College of Education for Pure Science (Ibn Al-Haitham), University of Baghdad. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License A Comprehensive Synthesis and Characterization via the Chemical Sol-Gel Method Firas Salim Abed1* and Lamia K. Abbas2 1,2Department of Physics, College of Science, University of Baghdad, Baghdad, Iraq. *Corresponding Author. Received: 17 April 2024 Accepted: 2 September 2024 Published :20 April 2025 doi.org/10.30526/38.2.3979 Abstract This research presents a synthesis approach for BSCCO superconductor with barium (Ba) substitution, involving a minor substitution at a fixed ratio of lead (Pb) and europium (Eu) through the chemical sol-gel method. The systematic exploration involves incorporating 0.1 of Eu instead of Bi into the BSCCO matrix to comprehend its impact on superconducting properties and the feasibility of producing superconducting material using the sol-gel route. Superconductor samples denoted as Bi1.6Pb0.3Eu0.1Sr2-yBayCa2Cu3O10+δ, where y varies from 0.0 to 0.3, were prepared. The investigation focused on understanding the effect of partially substituting Ba for Sr on superconducting properties. Transmitted electron microscopy (TEM) results revealed the creation of nanoparticles with an average diameter of 104.7 nm using the sol-gel technique. X-ray diffraction (XRD) analysis exhibited mainly the high-Tc phase (2223) compared to the low phase (2212) and a higher a/c ratio was observed at y=0.1. Electrical resistivity measurements demonstrated an improvement in critical temperature (Tc), reaching 113 K, and an increase in oxygen content at the same ratio. This comprehensive investigation explores the influence of Ba substitution on the structural and superconducting properties of the BSCCO system prepared by the sol-gel technique for further exploration and optimization of these HTS for specific applications. Keywords: BSCCO Superconductor, Sol-gel, High-temperature phase, XRD, TEM. 1. Introduction Unconventional superconductivity in cup rate compounds (which include copper oxide layers) remains a focal point of continuing research, as evidenced by numerous studies (1). The exact mechanism of high-temperature superconductivity remains an active area of research and is not fully understood (2). The role of the layered structure and the interactions between the layers, particularly in materials containing CuO2 planes, is a significant focus of the investigation (3). The specific arrangement of the CuO2 planes and the interactions between them play a crucial role (4). Electrons move through these layers, and the interaction between adjacent layers is believed to be essential for the emergence of superconductivity (5). Superconducting behavior is thought to arise from the interaction between the electrons and the crystal lattice (6). Specifically when the temperature is lowered below a critical temperature https://creativecommons.org/licenses/by/4.0/ https://creativecommons.org/licenses/by/4.0/ https://orcid.org/0009-0003-4135-6396 mailto:firas.abd2204p@sc.uobaghdad.edu.iq https://orcid.org/0009-0001-3100-9679 mailto:lamia.abbas@sc.uobaghdad.edu.iq IHJPAS. 2025,38(2) 116 (Tc) (7), consequently, it is assumed that the critical temperature (Tc) of these materials can be manipulated by altering the electronic configuration of the CuO2 planes, typically achieved through doping, thereby influencing the oxygen content within the compound (8). This way of research holds promise for the development of high-temperature superconductors with tailored properties. One of the most prominent materials in this field, bismuth-based superconductors, has received significant attention due to its high critical temperatures, which hold promise for applications in different fields such as magnetic resonance imaging (9, 10). The pseudo- tetragonal Bi-2223 unit cell is the fundamental structure of a high-temperature BSCCO system. However, obtaining a high-Tc (2223) single phase remains challenging. Nevertheless, it remains imperative to explore strategies to maximize the proportion of the (2223) phase within the material to elevate the critical temperature (11,12). Recent research suggests that partially melting Pb-doped materials and substituting Pb for Bi can significantly accelerate phase formation kinetics and enhance the yield of the Bi-2223 phase (13,14). Additionally, the superconducting behavior can be further optimized by double doping with additional elements (15). Achieving a homogeneous distribution of constituent parts within the sample is crucial for effective doping. Solid-state thermochemical processes stand out as the primary technique for fabricating ceramic superconductors (16), while alternative methods such as sol-gel procedures offer alternative routes to achieving a homogeneous mixture (17,18). The objective of this study is to investigate the correlation between the synthesis of Ba-substituted BSCCO using the sol-gel technique and their performance, suggesting a pathway for further advancements in high-temperature superconductors (19). The characterization of the synthesized samples involves an examination of their structural, morphological, and superconducting properties (20). Through the variation of the substitution factor and the application of advanced characterization techniques (21). This study offers insights into doping-induced changes in the crystal structure and superconducting transition temperatures (22). 2. Materials and Methods Chemical sol-gel was employed to prepare Ba-modified BSCCO superconductor samples with Eu and Pb presence with the general formula Bi1.6Pb0.3Eu0.1Sr2-yBayCa2Cu3O10+δ at different values of y of 0, 0.1, 0.2, and 0.3. A set of raw materials of Bi(NO3)2·5H2O, Eu(NO3)2 Pb(NO3)2, Sr(NO3)2, Ba(NO3)2, Ca(NO3)2·4H2O, and Cu(NO3)2·3H2O, were used in their specified molar ratios. Ethylenediaminetetraacetic acid (EDTA) was utilized as a complexing agent, while urea served as a fuel at 0.7 molar ratios. Ethylene glycol (EG) was used as a binding agent with a cationic component of 3. The solvent system comprised nitric acid and distilled water. The synthesis procedure was initiated by introducing the nitrite salts dissolved into a specific volume of distilled water, followed by the addition of nitric acid. Each component's weight was according to its molar content in the samples. The resulting mixture was stirred at 45°C, and ethylene glycol was dissolved in a specific volume of distilled water, which was then combined with ethylenediaminetetraacetic acid (EDTA) to induce precipitation. Ammonium hydroxide (NH3OH) was added to the primary liquid at 60°C until a pH of 7 was achieved, preventing precipitation and transforming the solution into a gel. This process was iterated for subsequent samples, and the resulting gel was further treated with the addition of urea. The gel underwent drying on a hot plate with gradual heating from 60 to 250°C in air, yielding a black-gray powder over 72 hours. A calcination procedure lasting six hours at 800° C was employed to eliminate residual nitrates, resulting in the formation of the final black BSCCO powder. This powder was homogenized using a gate mortar for half an IHJPAS. 2025,38(2) 117 hour. Then, pellets were fashioned from the powder samples using a hydraulic piston at 10-ton pressure. The pellets underwent a sintering process at 850°C for 48 hours, making them ready for subsequent characterization. The prepared samples were examined using X-ray diffraction analysis (SHIMADZU) to study structural properties such as the percentage of the high- temperature superconducting (HTS) phase and lattice parameters. The nano superconductors created were investigated using transmission electron microscopy (TEM) (Lasertec Corporation). Electric characterization was carried out using the four-probe method with the assistance of liquid nitrogen and a thermocouple. The critical temperature was determined by connecting electrodes to a Keithley instrument. 3. Results and Discussion Figure 1 presents the x-ray diffraction patterns for Bi1.6Pb0.3Eu0.1Sr2-yBayCa2Cu3O10+δ samples, showing the impact of varying y factors. The diffraction patterns reveal a dual presence of both 2223 and 2212 phases within the samples. The percentage of the high- temperature superconductor phase 2223 changes with the partial substitution of Ba for Sr, as detected through diffraction peak intensities associated with the two phases. It's worth noting that in the diffraction patterns, there are weak diffraction peaks corresponding to an unidentified phase, indicating the possible presence of additional crystalline structures or phases. Figure 1. XRD patterns of Bi1.6Pb0.3Eu0.1Sr2-yBayCa2Cu3O10+δ at different values of y. The investigation showed a peak HTS percentage of 75.99% for the 2232 phase at an optimal substitution factor of y=0.1. The certain dopant ratio may introduce necessary changes in the electronic structure of the material, promoting superconductivity. This can include enhancing the density of charge carriers by adding additional electron carriers, modifying the Fermi surface, or affecting the electron-phonon coupling, all of which contribute to an increase in the critical temperature (Tc) for superconductivity by facilitating electron movement without resistance. However, a subsequent increase in Ba substitution resulted in a decline in the HTS IHJPAS. 2025,38(2) 118 percentage. High substitution ratios can introduce disorder into the crystal structure, disrupting the coherence of the superconducting state. This disorder can impede the formation and movement of Cooper pairs, leading to a reduction in superconductivity, as discussed in a previous study (15). The higher Ba content leads to increased cuprite vacancies, causing enhanced scattering of super electrons within the crystalline structure (23). The diffraction peak positions observed in the samples exhibit slight variations with varying Ba content. The lattice constants were determined within the orthorhombic system by analyzing the diffraction peak positions. The variations in these lattice parameters concerning Ba content are graphically represented in Figure 2. For the sample with y=0 (no Ba substitution), the lattice parameters were found to be a=5.5203 Å, b=5.3183 Å, and c=36.7183 Å, closely resembling the values associated with the Bi-2201 phase. The heat treatment process induced reactions between the precursor and the added oxide, leading to variations in the lattice parameters. This can be attributed to the variance in ion diameter between the Ba dopant and the substituted ions of Sr, contributing to alterations in lattice constants and induced effects on other properties (24). Table 1 provides a detailed account of the variations in lattice parameters (a, b, and c) with different Ba content. Moreover, Table 1 includes calculations of the c/a ratio and unit cell density (ρ) based on these lattice parameters (25), providing supplementary insights into the structural modifications brought about by Ba substitution. The recorded variations in lattice parameters and associated ratios reveal a notable peak in the c/a ratio at y=0.1, reaching 6.6649. This aligns with the higher observed HTS% at the same substitution ratio. This correlation underscores the significance of Ba substitution in influencing both the structural aspects and superconducting characteristics of the material (26). Table 1. XRD parameters of Bi1.6Pb0.3Eu0.1Sr2-yBayCa2Cu3O10+δ at different values of y. y a (Å) b (Å) c (Å) V (Å3) c/a w (g/mole) ρm (g/cm3) HTS % 0 5.5203 5.3183 36.7183 1078.004 6.6515 1017.752 6.2700 57.08% 0.1 5.4147 5.3105 36.0884 1037.711 6.6649 1022.723 6.5453 75.99% 0.2 5.5349 5.2927 36.4884 1068.895 6.5925 1027.694 6.3852 62.47% 0.3 5.5012 5.3023 36.6131 1067.979 6.6555 1032.665 6.4216 47.34% Figure 2. Variation of HTS, and c/a with y of Bi1.6Pb0.3Eu0.1Sr2-yBayCa2Cu3O10+δ. Figure 3 displays a Transmission Electron Microscopy (TEM) image of the Bi1.6Pb0.3Eu0.1Sr2Ca2Cu3O10+δ, accompanied by a histogram illustrating the particle diameter next to the image. The TEM image reveals the successful preparation of nanoparticles by the IHJPAS. 2025,38(2) 119 sol-gel technique, exhibiting nearly spherical shapes ranging in diameter from 50 to 250 nm. The particle size exhibits a uniform distribution, with an average diameter of 104.7 nm. Figure 3. TEM image (a) and particle size distribution (b) of Bi1.6Pb0.3Eu0.1Sr2Ca2Cu3O10+δ prepared by Sol-gel. Figure 4 displays the EDS analysis for the Bi1.6Pb0.3Eu0.1Sr2Ca2Cu3O10+δ samples prepared at different y values. The patterns show emission peaks corresponding to each atom. Figure 4. EDS spectra of Bi1.6Pb0.3Eu0.1Sr2-yBayCa2Cu3O10+δ at different values of y. Table 2 lists the atomic ratio for each element in the four samples and the measured atomic ratio corresponding to all atoms within the samples of 19 atoms, compared with the IHJPAS. 2025,38(2) 120 stoichiometric ratios of each sample as listed in the general formula of Bi1.6Pb0.3Eu0.1Sr2Ca2Cu3O10+δ. The excess oxygen content in superconductors, beyond its stoichiometric ratio (δ), plays a crucial role in determining superconducting properties. In a pure BSCCO system, the excess greater than 10 arises from transferred electrons from Cu to the BiO layer, leading to the generation of holes on Cu and electrons on Bi. The changes in the valence state of Bi induced by the surplus oxygen result in alterations in hole carriers within the Cu–O2 planes. Consequently, it is anticipated that the predominant excess of oxygen will be situated in the Cu–O2 planes (27, 28). The oxygen ratio has its maximum ratio at y=0.1, followed by a reduction with further increases in y. This suggests a higher increase in oxygen beyond stoichiometric values for the 2223 structure, attributed to a more oxidized state of Ba2+ ions compared to Sr2+ ions (29). Table 2. EDS analysis of Bi1.6Pb0.3Eu0.1Sr2-yBayCa2Cu3O10+δ at different values of y, the atomic ratio, and compared with the stoichiometric ratios. y Element O Ca Cu Sr Eu Ba Pb Bi 0 Atom% 53.8 16.39 11 11.61 0.7 - 0.72 5.78 Measured ratio 10.22 3.11 2.09 2.21 0.13 - 0.14 1.10 Stoch. ratio 10 3 2 2 0.1 - 0.3 1.7 0.1 Atom% 54.55 14.77 11 9.9 0.73 0.6 1 7.45 Measured ratio 10.36 2.81 2.09 1.88 0.14 0.11 0.19 1.42 Stoch. ratio 10 3 2 1.9 0.1 0.1 0.3 1.7 0.2 Atom% 54.16 15.33 9.9 9.5 0.83 1.02 1.52 7.74 Measured ratio 10.29 2.91 1.88 1.81 0.16 0.19 0.29 1.47 Stoch. ratio 10 3 1.9 1.8 0.1 0.2 0.3 1.7 0.3 Atom% 54.03 15.8 9.65 8.86 0.7 1.55 1.24 8.17 Measured ratio 10.27 3.00 1.83 1.68 0.13 0.29 0.24 1.55 Stoch. ratio 10 3 1.9 1.7 0.1 0.3 0.3 1.7 Figure 5 displays the electrical resistivity as a function of temperature for the Bi1.6Pb0.3Eu0.1Sr2Ca2Cu3O10+δ samples at different y values. The rapid decline in resistivity as the temperature nears the critical temperature indicates the superconducting properties of the samples; the sudden decrease in resistance at Tc is caused by the creation of Cooper pairs of electrons, which can flow without any resistance below Tc. This is accompanied by the creation of an energy gap, which enables the dissipation-free flow of supercurrents (30). The critical temperature (Tc) values for each sample are detailed in Table 3. It is observed that the highest Tc value, reaching 113 K, is attained when y equals 0.1. IHJPAS. 2025,38(2) 121 Figure 5. Variation of sample resistivity with a temperature of Bi1.6Pb0.3Eu0.1Sr2-yBayCa2Cu3O10+δ at different values of y. Table 3. Tc values of Bi1.6Pb0.3Eu0.1Sr2-yBayCa2Cu3O10+δ at different values of y y=0 y=0.1 y=0.2 y=0.3 Tc (K) 111 113 112 112 4. Conclusion Thin films of Bi1.6Pb0.3Eu0.1Sr2-yBayCa2Cu3O10+δ superconductor with (y=0.0, 0.1, 0.2, and 0.3) were obtained using the sol-gel method. XRD analysis reveals that deposited films exhibit polycrystalline multiphase formation with an orthorhombic phase. TEM provided thin films prepared in the nanoscale range. The value of the critical temperature obtained for different compositions demonstrated the dependence of Tc on the substitution of Ba ions, with the highest Tc value of 113 K achieved for y = 0.1, which shows an increasing behavior with the increase of Ba ratio, and these values for bulk specimens are higher than those for film specimens. We should mention that both the specimen's bulk and films showed a superconductor. Acknowledgment We would like to express our special thanks to Dr. Amal Kadhum Jasim and Mr. Mohanad A. Aswad for their support. Conflict of Interest There is no conflicts of interest. Funding Financial support in preparation for the publication is based on the corresponding author. 0.0000 0.0002 0.0004 0.0006 0.0008 0.0010 0.0012 0.0014 0 50 100 150 200 250 300 ρ (Ω .c m ) T (K) y=0 y=0.1 y=0.2 y=0.3 IHJPAS. 2025,38(2) 122 Ethical Clearance Ethics of scientific research were carried out by the international conditions followed in dealing with laboratory animals and included animal health, husbandry and care for it, and providing appropriate conditions for it in terms of food, and appropriate methods were adopted in dealing with it when experimenting, and this is consistent with the instructions of the Iraqi Ministry of Health and Environment. References 1. Stryczewska HD, Stępień MA, Boiko O. Plasma and Superconductivity for the Sustainable Development of Energy and the Environment. Energies (Basel). 2022;15(11):4092. https://doi.org/ 10.3390/en15114092 2. Hayden SM, Tranquada JM. Charge Correlations in Cuprate Superconductors. 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