THE SURFACE-CHEMISTRY OF HG-CONTAINING SUPERCONDUCTORS BY HREM

The surface chemistry of Hg-containing superconductors has been invest igated using high resolution electron Microscopy. It was found that th e crystal surface of these materials usually decomposed in air by losi ng Hg, forming a thin amorphous layer containing Ba and Cu. This amorp hous layer can be recrystallised into some crystallites of barium cupr ate under the electron beam annealing. Such recrystallisation did not take place on the surface of Re-doped Hg-1201. Crystals decomposed hea vily when they were ground in solvents. A surface dependence of the lo w temperature low field magnetic susceptibility of Hg-1201 was also ob served.