Refinement of fundamental characteristic properties with homovalent Er/Y partial replacement of YBa2Cu3O7−y ceramic matrix

Highlights: • Defining optimum homovalent Er/Y substitution level for Y-123 ceramic materials. • Effect of Er/Y substitution on strengths of ability and quality of crystal structure. • Change of super-electrons in homogeneous cluster percentages with Er/Y substitution. • Phase transition from orthorhombic to tetragonal crystal system with excess Er ions. • Transition of intrinsic over-doped state into optimally doped state with Ga impurity. -- Abstract: In the current work, the effect of partial substitution of Er-sites for the Y-sites in the bulk YBa₂Cu₃O_7−y (YBCO) crystal system on the fundamental superconducting, electrical, crystallinity and structural morphology features is examined together with the reasons by means of powder X-ray diffraction (XRD), temperature-dependent electrical resistivity (ρ-T), scanning electron microscopy (SEM), electron dispersive X-ray (EDX) investigations and deduced calculation parameters. All the experimental test results show that the erbium impurities are successfully substituted by the yttrium sites in the bulk Y-123 crystal system, confirmed by sensitively the EDX and ρ-T measurement results. Moreover, it is found that all the fundamental characteristic quantities improve with the increment in the Er/Y partial substitution level up to the value of x = 0.03 beyond which the features tend to degrade dramatically. In this respect, the bulk Y_1−xEr_xBa₂Cu₃O_7−y ceramic compound prepared within the molar ratio of x = 0.03 crystallizes in the orthorhombic space group P_4/mmm with a little distortion due to the refinement in the crystallinity quality, crystallite growth, oxygen ordering degree, scattering mechanism, intra and inter-grain boundary couplings, grain alignment distributions and orientations. The XRD results show that the optimum erbium content enables to develop seriously the fundamental crystallographic features (lattice strain, lattice cell constants, crystallite size distribution, dislocation density ratio, oxygen concentrations in the unit cells) of Y-123 crystal structure. However, the excess Er/Y substitution leads to enhance considerably the systematic structural problems and inhomogeneous distribution of strains (formed by the structural defects) in the YBCO crystal structure. Thus, the phase transition from orthorhombic to tetragonal (structural O–T transition) crystal structure is observed. In fact, the XRD result displays that the trivalent Er³⁺ particles may partially be replaced by the divalent Cu²⁺ host atoms in the bulk Y-123 crystal structure after the critic substitution level of x = 0.03. The optimum Er concentration causes to form more thermodynamically activated super-electrons in the homogeneous superconducting cluster percentages in the paths due to the induced polaronic effect, and accordingly the intrinsic overdoped nature of Y-123 ceramic system transits into optimally doped state. Similarly, the erbium ions enable to increase the mobile hole carrier concentration and homogeneities in the oxidation state of superconducting grains. Namely, the amplitude of pair wave function (Ψ = Ψ₀e^-iφ) is strength enough to form bipolarons in the polarizable lattices and localize of densities of electronic states (DOS) at Fermi level. SEM investigations picture that the surface morphology view and crystallinity quality develop remarkably with the increment in the erbium content up to the critical dopant level of x = 0.03 where the sample exhibits the best grain alignment orientations, densest and smoothest surface morphology with the combination of lowest porous and largest particle distributions well linked each other. All in all, this comprehensive work based on the analysis of Er/Y partial replacement mechanism along the YBa₂Cu₃O_7−y ceramic matrix may open up a newly/novel and feasible area for the advanced engineering, heavy-industrial technology and large-scale applications of type-II superconducting materials.