A MODEL FOR THE CRYSTAL-GROWTH OF YBA2CU3OY

The crystal growth and crystal morphology are very important propertie s of YBa2Cu3Oy, superconductors. In this work, we approach these probl ems with polycrystals. Several typical crystal morphologies were obser ved by scanning electron microscopy, and the terraced crystals with a layer-by-layer structure were found to be the major form for the well- grown YBa2Cu3Oy. To interpret the results, a step-growth model was pro posed. In this model, each crystal terrace is close-packed with crysta l particles in order. And the particles, each consisting of tens of cr ystal cells, are movable during crystal growth. Particles at edges or margins of small crystals can move to their larger neighboring crystal s through diffusion. With this particle diffusion, small crystals vani sh and large crystals grow larger. This proposed model is confirmed by experimental observations.