Double partial substitution effect of silver (Ag) and strontium (Sr) on the structural and electrical properties of high temperature Bi2-xAgxBa2-ySryCa2Cu3O10+δ superconductor

Superconductor samples with the chemical composition Bi2-xAgxBa2-ySryCa2Cu3O10+δ were synthesized using solid-state technology and the effect of partial substitution of Sr (y=0, 0.1, 0.2, 0.3, 0.4) and Ag (x=0, 0.2) on their electrical and structural properties was investigated. X-ray diffraction analysis showed that all samples have the tetragonal crystal structure with the largest lattice constant (c) at x = 0.2 and y = 0.1. Electrical resistance measurements using the four-probe method showed the critical temperatures Tc(1)=127.5 K and Tc(2)=152.7 K (Tc) for the pure sample (x=0, y=0). When introducing Ag and Sr in the optimal concentration ratio (x=0.2, y=0.1), the Tc values increased significantly reaching Tc(1)=139.2 K and Tc(2)=170.5 K. This is explained by the regularization of the crystal structure, as evidenced by the increase in the c-axis length and the oxygen percentage (δ). However, as the Sr concentration ratio further increased (from x=0.2, y=0.2 to x=0.2, y=0.4), the Tc values tended to decrease, with the lowest values being Tc(1)=134.9 K and Tc(2)=163.2 K at (x=0.2, y=0.4). This decrease was attributed to the introduction of Cu-O impurities, which disrupted the crystal structure. Overall, the study identified the concentration ratio (x=0.2, y=0.1) as the most favorable for achieving the highest Tc, confirming its potential for improving the superconducting properties of the material. The samples were classified as type II superconductors.