A semi-quantitative method to analyze the complex pinning mechanisms in single-grained high-Tc superconductors

To clarify the relationship between J_c-H performance and microstructure, a determination of the flux pinning mechanism is necessary. However, multiple active pinning centers originating from different crystalline or chemical inhomogeneities may co-exist in most bulk high-T_c superconductors. This study presents a method to analyze the volume pinning forces of single-grained high-T_c superconductors with multiple additives (i.e. multiple pinning mechanisms) by means of the scaling theory of volume pinning force F_p(H). The J_c-H curves as well as F_p/F_p,max vs. h^p(1-h)^q curves, where F_p,max is the maximum volume pinning force, h=H/H_irr, and the parameters p and q depend on the characteristics of flux pinning can be divided into two parts with different pinning mechanisms, i.e. J_cδTc (Δκ pinning) and J_cδl (normal pinning), respectively. By comparing the magnitude of the pinning force attributed to J_cδTc and J_cδl, respectively, a semi-quantitative description of complex pinning behavior of single-grained superconductors with multiple pinning mechanisms can be obtained. It is found that the dominant pinning mechanism of RE-Ba-Cu-O materials (REBCO, RE: Sm and Nd) with nano-scale 211 additions is δT_c pinning, while those with CeO₂ and Pt/CeO₂ additions is δl pinning. The relationship between these two pinning mechanisms with varying temperature and addition is also discussed.