Abstract
Microscopic observation has been conducted on newly discovered high Tc oxide superconductors using the polarized optical microscope. It was revealed that all the superconductors exhibited almost the same microstructure irrepective of the kind of the rare earth site. In the samples prepared in the usual sintering process, the grains are oriented at random and have rectangular shapes. In the sample with the orthorhombic structure, the grains contain twins, whereas no twin is observed in the tetragonal sample.
