摘要
Ⅰ. INTRODUCTION Bednorz and M(?)llerr discovered the superconductivity in La-Ba-Cu-O system for the first time. Afterwards, C. W. Chu and Zhao Zhongxian et al. obtained superconductor with zero resistance temperature about 90 K in Y-Ba-Cu-O system. Many scientists substituted other rare earth oxides for La or Y to obtain the