Comparative analysis of Tb and Zn doping effects on the microstructural and mechanical properties of YBCO-123 and YBCO-358 superconductors

Abstract

In this study, the microstructural and mechanical properties of copper-based superconducting systems synthesized via the sol-gel method-namely Y1-xTbxBa2Cu3O7-delta, Y1Ba2Cu3-xZnxO7-delta, Y3-xTbxBa5Cu8O18-delta, and Y3Ba5Cu8-xZnxO18-delta were comparatively investigated to evaluate the effects of varying concentrations of terbium (Tb) and zinc (Zn) dopants on the structural integrity, crystal quality, and micromechanical strength of both Y1-xTbxBa2Cu3O7-delta and Y3-xTbxBa5Cu8O18-delta superconducting phases. X-ray diffraction (XRD) assessed crystal structure, phase purity, and dopant effects, while scanning electron microscopy (SEM) characterized particle size distribution, surface morphology, porosity, and potential phase separation. Vickers microhardness (Hv) testing quantified micromechanical behavior under varying dopant concentrations. Results show that Zn and Tb substitutions influence crystal structure and mechanical strength differently depending on dopant level and superconductor type. Optimized doping enhanced phase purity, lattice stability, microstructural coherence, and hardness, whereas excessive doping caused lattice distortions, defect clustering, oxygen ordering instabilities, and partial phase separation. Y1-xTbxBa2Cu3O7-delta ceramics exhibited superior tolerance to both dopants, with improved crystallinity, grain connectivity, and mechanical robustness at higher concentrations. In contrast, the Y3-xTbxBa5Cu8O18-delta ceramic structure was more sensitive to doping, showing benefits only at low levels and significant structural degradation at higher levels, explaining the preference for the Y1-xTbxBa2Cu3O7-delta phase in substitution studies. Analysis of load-independent Vickers hardness in plateau regions indicated that the Indentation-Induced Cracking (IIC) model most accurately described mechanical behavior. Consequently, precise optimization of dopant type and concentration is essential to achieving high structural integrity and mechanical performance, making these YBCO-based superconductors promising candidates for advanced energy and technological applications.