Correlation between dopant-induced structural distortions and performance characteristics in Tb- and Zn-substituted Y-358 ceramics synthesized via sol–gel route

Abstract This study systematically investigates the structural, microstructural, electrical, and magnetic properties of YBa 3 Cu 5 Cu 8 O δ (Y-358) superconducting ceramics with partial substitution of trivalent terbium (Tb³⁺) at Y³⁺ sites and divalent zinc (Zn²⁺) at Cu²⁺ sites. The compositions Y 3-x (Tb) x Ba 5 Cu 8 O 18-δ and Y 3 Ba 5 Cu 8-x (Zn) x O 18-δ (0.0 ≤ x ≤ 0.15) are synthesized via the sol–gel synthesis route and investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron dispersive X-ray (EDX), temperature-dependent resistivity ( ρ –T), and vibrating sample magnetometer (VSM) measurements, along with theoretical modeling. It is determined that all synthesized ceramic samples exhibit high current-carrying capacity and superior superconducting performance, supported by efficient charge transport, excellent crystalline quality, and uniform composition, all of which were achieved through the sol–gel method, an effective and reliable approach for producing advanced high-performance ceramics. XRD analyses reveal that both dopants influence phase purity, crystallinity, lattice parameters, and oxygen ordering degree, with Tb impurity substitution inducing more pronounced impurity phase formation and lattice distortions. SEM and quantitative histogram analyses demonstrate that Tb enhances grain boundary disorder, grain misorientation, porosity, and microstructural problems, while Zn promotes more uniform grain growth, especially at moderate substitution levels. EDX analyses confirmed the successful substitution of Y by Tb and Cu by Zn within the Y-358 ceramic lattice, evidencing effective dopant incorporation that correlates with improved/degraded microstructural uniformity and superconducting current pathways. ρ-T experimental results show that both Tb and Zn reduce the superconducting transition temperatures ( T c ) and broaden the transition width (Δ T c ), indicating increased structural disorder, perturbations of the pseudogap state, and reduced charge carrier concentration, and electronic density of states in Cu-O 2 planes. Notably, Tb doping causes a steeper decline in T c parameters and mobile hole carrier concentration ( p ), attributed to its larger ionic radius and stronger lattice strain effects. Magnetic hysteresis (M–H) measurements and critical current density calculations confirm a deterioration in flux pinning capacity and superconducting performance with increased doping, particularly in the Tb-substituted Y-358 ceramics. The normalized pinning force analyses further reveal that the dominant flux pinning mechanism shifts from normal point pinning to Δ κ -type with increasing impurity levels. Accordingly, the results demonstrate that although both dopants disrupt the Y-358 superconducting phase, Tb 3+ impurity has a more detrimental impact on phase stability, flux pinning, and superconducting properties due to its greater tendency to induce structural disorder. These findings underscore the critical role of dopant type and concentration in tailoring the functional properties of high-T c Y-based superconductors for potential applications in high-temperature superconducting systems, energy devices, and magnet-based technologies. Graphical Abstract