DIRECT OBSERVATION OF ATOMIC IMAGE OF HIGH Tc SUPERCONDUCTORS BY FIELD ION MICROSCOPY Q.J. GAO, Z.X. ZHANG, S.Y. XU, S.Q. FENG et S.Z. WANG J. Phys. Colloques, 50 C8 (1989) C8-487-C8-488 DOI: 10.1051/jphyscol:1989883