中文摘要：

利用定向凝固技术制备了取向良好的YBCO棒材，其a-b晶面与提拉方向的夹角小于5°。为研究YBCO生长的各向异性及其定向凝固机制，分别通过空淬及炉冷的方式获取了熔体生长的YBCO晶粒形貌及固液界面形貌。YBCO晶粒呈现片层状结构，其长厚比约为2～5。晶体生长的固液界面清晰反映出了外延生长的特征。基于上述结果，讨论了YBCO的定向凝固机制，认为YBCO的定向凝固是由择优生长及外延生长两阶段构成，这很好地解释了本文的试验结果。

英文摘要：

Well-orientated YBCO rod with the angle between the pulling direction and the a-b crystal face less than 5° was prepared by directional solidification technique. To investigate the growth anisotropy and solidification orientation of YBCO, samples which can exhibit the morphology of crystal grains and crystal growth transition region were also prepared by air quenching and furnace cooling method, respectively. Anisotropic lamellar YBCO crystal grains were obtained, the dimension ratio of about 2-5 between a- and/or b-axes and c-axis can be seen from these grains. A characteristic of epitaxial growth can be clearly seen from the furnace-cooled sample. Two steps involving preferential growth step and epitaxial growth step can be inferred for the directional solidification process of YBCO based on the above experiment results, which can well interpret the growth orientation of YBCO reported in this paper.