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 (0similar to1 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 Deltakappa 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 RE1+xBa2-xCu3Oy matrix, which are products of nm211 particles and liquid peritectic reaction, act as the source of Deltakappa pinning centers.