Growth of transient phases during Bi(2212) to Bi(2223) transformation
Hot stage X-ray measurements and hot stage environmental electron scanning microscopy (ESEM) measurements have been used to study the intermediate phases that grow as the Bi(2212) grains begin to transforms into Bi(2223). The primary purpose is to investigate transient phases that may appear at the interface between the Bi(2212) grains and a Ag overlay while the temperature is being ramped to the reaction temperature at a rate comparable to that used in the commercial processing of tape conductors. Pb-doped Bi(2212) is metastable and is found to decompose and recrystallize during the ramp up to the reaction temperature. In addition, above about 973 K (700 °C), hillocks are found to grow between the flat surfaces of the Bi(2212) grains and the Ag overlay. Scanning Auger measurements show that these hillocks are composed of crystals of (Sr,Ca)O about 100 nm in diameter and have a Sr/Ca ratio of about 1.5. This growth of hillocks occurs on the time scale of tens of minutes and it may temporarily deplete the Bi(2212) grains of Sr leaving them Ca rich.