Change of thermal, mechanical and morphological properties with yttrium addition to the crystal structure of the Bi-based superconducting parents

In the crystal structure of Bi2.0Sr2.0Ca1.1Cu2.0Oy (Bi-2212) produced by the standard solid-state method, the basic mechanical performance parameters, durable tetragonal phase, surface morphology appearances and mechanical characteristics of the newly formed matrices by substituting yttrium/bismuth at different mole ratios were determined. The changes were determined by Vickers hardness (Hv) and scanning electron microscope (SEM) measurements. Energy-dispersive X-ray (EDX) spectrometry results showed that yttrium ions were successfully added to the system at the desired stoichiometric ratios. According to the results obtained, all the discussed properties improved with the increase of yttrium (Y) doping ratio up to x = 0.01, while a decrease was found in the parameters above this value. Thus, it has been determined that if optimum Y ions are present in the Bi-2212 ceramic system, new chemical/ionic bonds, surface compressive residual stress regions and lattice stress fields are formed in the crystal structure. Again, the optimum Y additive stabilizes the tetragonal phase of the Bi-2212 ceramic material and controls the crack growth rate in the crystal lattice. Thus, the crystal lattice x = 0.01 indicates that the yttrium-doped sample is less sensitive to the applied force. Similarly, SEM photographs showed that the same material had the most homogeneous dense (less porous and smooth) surface and the best crystal structure. In addition, from SEM analysis, stacked layers, which are the general morphology image of Bi-2212, were formed with larger crystal sizes and it was observed that these layers had much stronger connections and more correct orientation. In addition, in the case of optimum yttrium doping of the lattice, an increase in the nucleation temperature due to low activation energy was detected in the crystallization mechanism of the Bi-2212 ceramic system. In this case, this material was found to have the highest thermodynamic unstability. It is emphasized that the improvements in all these properties can be explained by the Cu element distribution in the crystal lattice when looking at the EDX measurement results. Finally, load-independent microhardness values in the plateau boundary region were examined with semi-empirical mechanical models and reliable results were obtained. The most successful mechanical approach among the models was the notch-induced crack formation (IIC) method.