A Model for the Crystal Growth of YBa2Cu3Oy

The crystal growth and crystal morphology are very important properties of YBa2Cu3Oy superconductors. In this work, we approach these problems with polycrystals. Several typical crystal morphologies were observed 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 proposed. In this model, each crystal terrace is close-packed with crystal particles in order. And the particles, each consisting of tens of crystal cells, are movable during crystal growth. Particles at edges or margins of small crystals can move to their larger neighboring crystals through diffusion. With this particle diffusion, small crystals vanish and large crystals grow larger. This proposed model is confirmed by experimental observations.