Solubility limit of tetravalent Zr nanoparticles in Bi-2223 crystal lattice and evaluation of fundamental characteristic properties of new system

In this comprehensive work, we focus sensitively on the changes of microstructural, electrical, superconducting and mechanical properties belonging to the bulk Bi_1.7Pb_0.4Sr_2.0Ca_2.0Zr_xCu_3.1O_y materials with the different Zr nanoparticles (0 ≤ x ≤ 1.0) inserted in the superconducting matrix. The characterizations of the materials prepared are experimentally performed by bulk density, dc resistivity (ρ–T), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), electron dispersive X-ray (EDX) and Vickers microhardness (H _v ) investigations. It is found that all the characteristics given above (especially superconducting properties) degrade considerably with the increment in the Zr addition level, and in fact they reach to the global minimum points in case of the maximum dopant level. The main reason of the rapid decrement in the electrical and superconducting properties stems from the presence of the localization problem in the Cu–O₂ consecutively stacked layers. Likewise, the Zr foreign addition increases the artificial random defects, dislocations and grain boundary weak-links in the superconducting system, even being favored by the SEM examinations. At the same time, the EDX surveys indicate that the Zr nanoparticles in the tetravalent state prefer to substitute for the divalent states of the Cu inclusions through the crystal structure as a result of their close ionic radius values (86 pm for Zr⁴⁺ ion and 87 pm for Cu²⁺ ion). Thus, the differentiation of the electronegativity reduces the mobile hole concentration in the Cu–O₂ slabs. Additionally, the XRD experimental findings show that there is a systematic decrement in the Bi-2223 (high) phase up to the Zr concentration level of x = 0.70 beyond which new characteristics peaks of ZrO₂ appear immediately. This is in relation to the fact that the solubility limit corresponding to the Zr foreign impurity in the Bi-2223 system is about x = 0.70. Similarly, the regular decrement in both the c-axis length and crystallite size with the dopant confirms the deterioration of the superconducting properties. Furthermore, the dramatic reduction of the H _v values stems from the suppression of the crystallinity and connection quality in the intergrain coupling of the superconducting samples exhibiting typical Indentation Size Effect behavior due to the existence of both elastic and plastic deformations in the system.