摘要
Ⅰ. INTRODUCTIONA number of investigators have reported recently that crystal grains of RBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-x</sub> invariably contain at least one set of parallel（110）twin domain, where R represents La, Y, Eu and Tl. The grain with twin domain is confirmed to be a superconducting phase of orthorhombic structure. Twins of this kind are usually called transformation twins（in contrast to, for instance, growth twins or deformation twins and twin boundary）. However, de-
基金
Project supported by the Open Research Laboratory of High Performance Ceramics
Superfine Microstructural Studies
