The surface chemistry of Hg-containing superconductors by HREM

The surface chemistry of Hg-containing superconductors has been investigated using high resolution electron Microscopy. It was found that the crystal surface of these materials usually decomposed in air by losing Hg, forming a thin amorphous layer containing Ba and Cu. This amorphous layer can be recrystallised into some crystallites of barium cuprate under the electron beam annealing. Such recrystallisation did not take place on the surface of Re-doped Hg-1201. Crystals decomposed heavily when they were ground in solvents. A surface dependence of the low temperature low field magnetic susceptibility of Hg-1201 was also observed.