Using magnetic measurements we have investigated the effect of twin boundaries on flux pinning over the temperature range of 4.2 to 85 K in YBaCuO superconductors prepared by the melt-powder-melt-growth process (MPMG). It has been found that non-superconducting Y2BaCuO5 (211) particles dispersed in the 123 matrix can work as strong pinning centers, resulting in higher Jc values. Despite non-superconducting 211 particles being the main pinning centers, defects such as twin boundaries, oxygen deficiency and stacking faults are also considered to be possible pinning centers in melt-processed YBCO. An enhancement of Jc was observed when the magnetic field was applied parallel to the twin planes. The results indicate that twin planes contribute to flux pinning, but that their effect is not very large in MPMG processed samples.
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