Modification of YBa/sub 2/Cu/sub 3/O/sub 7-x/ ceramics by adsorbed water and other gases

Surface modification of vacuum scraped YBa/sub 2/Cu/sub 3/O/sub 7-x/ (x = 0,1) by H/sub 2/O, CO, CO/sub 2/ and O/sub 2/ was studied using photoemission and the modification of bulk YBa/sub 2/Cu/sub 3/O/sub 7/ and YBa/sub 2/Cu/sub 3/O/sub 6.25/ by liquid water was studied using x-ray absorption. Photoemission measurements show that H/sub 2/O reacts with the surface by dissociating to form a surface hydroxide. CO and CO/sub 2/ form surface compounds that may be carbonates. Molecular oxygen dissociates and readily enters the bulk after adsorption on oxygen deficient material. The x-ray diffraction and absorption studies show that H/sub 2/O readily reacts with oxygen deficient material and completely disrupts it. BaCO/sub 3/ and a CuO-like phase are detected. YBa/sub 2/Cu/sub 3/O/sub 7/ is more stable and was not disrupted. Modification of the Cu K-edge and EXAFs resemble those seen when the material reacts with H/sub 2/ and this suggests that hydrogen may be produced during the surface reaction with water and may react with the bulk material