TiO2 addition effect on flux pinning properties of bulk GdBa2Cu3O7-δ superconductors

TiO2 dilute doping in melt-processed GdBa2Cu3O7-delta bulk superconductors was studied. TiO2 fine particles are effective additive for the enhancement of flux pinning. TiO2 doping results in the enhanced delta l pinning and the improved T-c. Nevertheless, the pinning force characterizations show that delta T-c pinning still acts as the main role, which can be attributed to the clustered strong superconducting phases and the high B-irr values. The trapped field profiles clearly show that the enhanced flux pinning is realized in the doping range from 0.0 mol.% to 0.3 mol.%. Possible reasons behind them are discussed. The main reason is that Ti occupies the Cu site in the CuO chain and thus Ti substituted region forms the high T-c superconducting phase. On the other hand, owing to the enhanced strains or dislocations caused by ion substitution, this region also contributes to the enhanced delta l pinning. (C) 2012 Elsevier B.V. All rights reserved.