ROLE OF INTERMEDIATE PHASE FORMATION IN THE PREPARATION OF BA4Y2O7.CO2

The objective of this study was to determine the reaction conditions that facilitate optimal formation of Ba4Y2O7.CO2, a compound useful for the preparation of the high-temperature superconductor YBa2Cu3O7-x. Ba4Y2O7.CO2 powders were prepared by conventional, colloid, and coprecipitation powder processing methods to assess the impact of the preparation technique and consequent particle mixing on the Ba4Y2O7.CO2 formation mechanism and kinetics. The phase assemblage and phase purity were assessed as a function of solid-state reaction temperature (950-1150-degrees-C) and soak time (2.5-20 h). Phase-pure Ba4Y2O7.CO2 Was prepared with a 20-h soak at 1050-degrees-C. However, the powder synthesis method played no significant role in phase development. This surprising observation indicates that diffusion of the reactant species probably is not a factor in promoting formation of Ba4y2O7.CO2 as is observed in most solid-state reactions. Instead, Ba2Y2O5.2CO2 intermediate phase formation segregates the system to the extent that the degree of homogeneity imparted by all three synthesis methods is equivalent. Formation of the Ba2Y2O5.2CO2 intermediate may be related to nucleation and growth kinetics, which can be independent of the powder characteristics or mixedness of the system.