WETTING AND REACTIONS BETWEEN SILVER AND BULK YBA2CU3O7-X

Contact angles of Ag heated at 975°C and 990°C on hot-pressed YBa2Cu3O7-x were measured as a function of time and P(O2). Cross-section of the Ag-YBa2Cu3O7-x interfaces formed after the contact angle experiments were analyzed by scanning el ectron microscopy, electron-probe microanalysis and transmission electron microscopy. Wetting by Ag and its penetration into the YBa2Cu3O7-x microstructure is promoted by formation of the Ag-O eutectic liquid above 931°C. The eutectic liquid forms readily where the Ag is in contact with an oxygen-containing atmosphere. If that source of oxygen is insufficient, as in the interior of the YBa2Cu3O7-x, the Ag gains oxygen by reduction of YBa2Cu3O7-x. Y2BaCuO5 forms as a reaction product when the Ag-O eutectic liquid dissolves Cu from the YBa2Cu3O7-x. Ag electrical contacts made under the same conditions of time, temperat ures, and P(O2) as in the wetting experiments are ohmic. © 1990.