The investigation of structural, superconductivity and mechanical performances belonging to Al-added Bi-2223 superconductor ceramics

This comprehensive study investigates the change of the microstructural, electrical and superconducting properties of the Bi1.8Sr2Ca2.2Cu3.0AlxOy ceramic cuprates produced by the conventional solid state reaction method at the constant annealing temperature of 840 °C for 24 h with the aid of the standard characterization measurements such as bulk density, dc resistivity (q-T), transport critical current density (Jc), X-ray diffraction (XRD) and Vickers microhardness examinations. The results obtained confirm that all the properties degrade with the enhancement of the Al concentration level in the Bi-2223 superconducting system because of not only the distortion between the Bi-2223 slabs but also the increase in the porosities and grain boundary weak-links. For example; the onset (offset) critical temperature retrogrades from 109.61 K (107.18 K) to 92.63 K (13.41 K) depending on the augmentation of the Al concentration level. However, the transport critical current density is measured in the range from 81 A/cm2 (for pure sample) to 17 A/cm2 (for Al-6 sample). Moreover, one can see from the XRD measurements that Al particle introduces into the crystal structure by reducing the formation velocity of the Bi-2223 phase. As for Vickers microhardness measurements, the presence of Al impurities in the crystal structure diminishes remarkably the mechanical performance. In fact, the enhancement Al concentration level damages constantly the key mechanical design properties such as the mechanical durability, hardness, ductility, toughness, stiffness, fracture and especially flexural strengths due to new induced structural problems including the local microstructural distortion, porosity, misorientations (grain alignment distributions), defects, lattice strains, structural inhomogeneity and grain boundary coupling problems in the crystal matrix. Further, the mechanical characterization and microhardness values of the samples produced are analyzed by Meyer's Law, Proportional Sample Resistance (PSR) Model, Elastic/Plastic Deformatin (EPD) Model and Hays-Kendall (HK) Model. According to the experimental results obtained, HK model is the best model for microhardness calculations of the samples prepared for this study. As a result, the microstructural, electrical and superconducting properties of Bi1.8Sr2Ca2.2Cu3.0AlxOy ceramics degrades slowly with the enhancement of the Al dopant level.