Effect of Nano-Sized Sm₂BaCuO₅ Particles Addition on the Pinning Mechanism of Sm–Ba–Cu–O Materials

The superconducting properties of air-processed melt-textured growth Sm–Ba–Cu–O samples with addition of small amounts (0.004 wt%, 0.4 wt%, 4 wt%) of nano-sized Sm₂BaCuO₅ particles (nm211) were studied. The microstructure observations show that the size distribution and morphology of the 211-particles of the nm211-doped samples are similar to that of the control (undoped) samples. However, except for the 4 wt% nm211-doped sample, both T_c (critical temperature) and J_c (H, T) (critical current density) are enhanced in nm211-doped samples, and the J_c–H curves are different from those of control samples. The effect of nm211 particles on J_c enhancement is larger at high magnetic fields (>1 T at 77 K) than at low magnetic fields (0∼1 T). The dominant pinning mechanism by analyzing the J_c (H, T) data using the scaling theory indicate that the nm211-doped samples are originated from Δκ pinning (i.e., T_c variation); on the other hand, the control samples are originated from normal pinning (i.e., nonsuperconducting crystalline defects). It is proposed that nano-sized compositional fluctuations in the RE_1+x Ba_2−x Cu₃O _y matrix, which are products of nm211 particles and liquid peritectic reaction, act as the source of Δκ pinning centers.