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,(H). The J(c) - H curves as well as F-p/F-p,F-max vs. h(P)(l - 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(c delta Tc) (Delta K pinning) and J(c delta l) (normal pinning), respectively. By comparing the magnitude of the pinning force attributed to J(c delta Tc) and J(c delta l), 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 delta T-c pinning, while those with CeO2 and Pt/CeO2 additions is delta l pinning. The relationship between these two pinning mechanisms with varying temperature and addition is also discussed.