Effect of homovalent Bi/Ga substitution on propagations of flaws, dislocations and crack in Bi-2212 superconducting ceramics: Evaluation of new operable slip systems with substitution

Abstract

This study defines a strong methodology between the mechanical performance behaviors and formation of possible operable slip systems in the crystal structure of Bi-2212 superconducting phase with trivalent Bi/Ga substitution with the aid of Vickers hardness tests exerted at various indentation load intervals 0.245 N–2.940 N. It is found that the mechanical performance behaviors improve regularly with the increment in the trivalent Bi/Ga partial substitution level up to the value of x = 0.05 due to the formation of new operable slip systems. Namely, the optimum gallium (Ga) impurities serve as the strain fields and associated forces for the interaction of dislocations within the different orientations with each other to impose the surface residual compressive stresses orienting favorably the superconducting grains. Thus, the propagation of dislocations, flaws and cracks divert in the crystal structure. On this basis, the presence of optimum Ga impurity in the Bi-2212 crystal system strengthens the mechanical strength, critical stress, resistance to the plastic deformation, stiffness and durability nature. Moreover, the experimental results advance in-depth understanding of fundamental links between the porosity and Young's moduli of elasticity founded on the impurity level and applied test loads. It is observed that in case of the optimum level of x = 0.05 the propagation of flaws, dislocations and cracks proceed along the transgranular regions instead of the intergranular regions as a consequence of improvement in the durable tetragonal phase. On the other hand, the excess Ga content level in the polycrystalline Bi-2212 system results in the augmentation in the stress raisers, crack surface energy and crack-initiating flaws, activating the stress-induced phase transformation.