SEM study of nanosize defects in powder-formed YBCO
Abstract
It is postulated that nanosize defects in YBCO increase the critical current in the superconductor. Superconducting YBCO microstructure is investigated via SEM and has been found to be polycrystalline and granular with a predominantly square-faceted structure with occurrences of hexagonally-formed crystals. Defect occurrence has been found to be multiple and varied, showing fractures, delaminations, cracks, porosities and twinning. Twinning in its different forms was observed to be predominant. Twinning of the contact type where two or more crystals are attached were the most predominant. Growth of a smaller crystal on the face of a larger crystal called "piggy-back" twins and crystal intergrowth twins called penetration twins were also commonly observed. Twins of the mirror type, or "Siamese" type was rarely observed.