Influence of antiphase boundaries on critical current densities in YBa2Cu3O7-y single crystals

Twinned and detwinned YBa2Cu3O7-y (Y123) single crystals were observed by t ransmission electron microscopy to investigate the influences of the lattic e defects on the peak effect for Y123 single crystals. Twin boundaries with the spacing of 0.2-0.5 mum were seen only in the twinned Y123 single cryst als. Antiphase boundaries (APBs) along the (110)(Y123) plane were observed in both twinned and 0.5h-detwinned samples, which showed the peak effect in high magnetic field over 3 T at 70 K. In contrast, APBs were not found in 100h-detwinned sample. Critical current densities of this sample were small all over the range of the applied magnetic field. In conclusion, we sugges t that APBs have a significant influence on the peak effect of Y123 single crystals in the high magnetic field.