Effect of Y-Ca substitution on microstructural morphology and critical current density in YBa2Cu3O6.8 ceramics

Abstract

Heterovalent element substitution is an effective way to optimize functional properties of the Y-Ba-Cu-O high-temperature superconductors. In this study, we analyze the effect of Y-Ca substitution on microstructure and critical current in YBa2Cu3O6.8 ceramics with transmission electron microscopy and magnetometry. The obtained results reveal that the substitution of Y3+ by Ca2+ initiates the formation of complicated microstructure consisting of Y(Ca)-123 matrix with multiple defects of different types and fine nanoscale Y-211 particles coherently coupled with the matrix. Depending on Ca doping, various microstructural defects such as dislocations, stacking faults, and effects associated with cationic disorder are observed. The magnetic and superconducting properties in Ca-substituted compositions Y-123 are discussed in terms of the sample microstructure morphology and the specificity of coupling between the basic Y(Ca)-123 phase and impurity particles of the Y-211 phase. We find that shape type and dispersion of the Y-211 precipitations are crucial to regulating both the critical current and the critical temperature in the ceramics.