Intragranular Critical Current Density in YBCO Substituted with Pr or/and Ca

摘要

The effect of magnetic (Pr) and non-magnetic (Ca) chemical substitutions on the intragranular critical current, J_(intra,c), in polycrystalline Y_(1-x-y)Pr_xCa_yBa_2Cu_3O_(7-δ) samples is studied. In principle two factors limit the J_(intra,c): decoupling critical current density J_0 ～ H_c/λ (H_c –thermodynamical critical field,λ-London penetration depth) and pinning force. It is shown that at 4.2 K and low concentration (x=0.05, y=0 and x=0, y=0.025) both substitutions are almost equally effective and lead to Jintra, c higher than that for the non-substituted sample. This is a result of generated nanometric substitutional defects, increasing the pinning in both cases. The non-magnetic, low valence Ca~(2+) substitution increases the carriers and leads to small overdoping, while the magnetic (Pr~(3+)) substitution only slightly deteriorates decoupling current. At high concentrations (x=0.20, y=0 and x=0, y=0.25) J_(intra,c) decreases in comparison with the non-substituted sample due to decoupling current suppression in both cases. It is also established that low Pr concentration gives the highest J_(c,intra) at fields higher than 1 T when the temperature is raised to 20 K.