Liquid and solid solubility of Ag in Bi2Sr2CaCu2O8

Currently, the leading candidates for usable high temperature superconducting wires are Bi-Sr-Ca-Cu-O tapes produced by modifying the powder in tube process. In order to obtain crystallographic texture, these tapes are processed by partial melting then slow cooling through the peritectic. While it is well known that Ag suppresses the lowest liquidus temperature of the Bi based materials, no serious investigation of the Bi-Sr-Ca-Cu-O-Ag phase diagram has been undertaken. Solubilities of Ag in Bi2212 melt was determined by ICP-AES and TEM/EDS on samples of Bi2212 and 20 wt.% Ag which were melt-spun in air at temperatures of 900 to 1,200 C. The most prominent feature of the phase diagram was found to be a liquid immiscibility at all temperatures. There exists a eutectic on each side of this gap. For the Ag rich side the eutectic is at 98 at. % Ag and depresses the melting by 15C over that for pure silver for the same oxygen partial pressure. The oxide rich eutectic contains no more than 4 at. % Ag and depresses the solidus by 30C. The solid solubility of Ag in Bi-Sr-Ca-Cu-O glass (oxide glass) is found to be less than the detection limits of TEM/EDS and Ag is systematically excluded from the oxide glass