Characterization of Ba sub 2 YCu sub 3 O sub x as a function of oxygen partial pressure Part I: Thermoanalytical measurements.

The equilibrium oxygen content, X, in the range 6 X 7 is described for the high temperature superconductor Ba sub 2 YCu sub 3 O sub x as a function of P sub O sub 2 and temperature over the ranges 10 sup (-3) P sub O sub 2 1 atm. and 400 C 1000. The results are expressed as a series of isocompositional lines on plots of log P sub O sub 2 versus reciprocal temperature. Enthalpy for the oxidation as derived from the slopes of these lines is found to vary from 24 to 26.5 kcal mol sup (-1) (per oxygen atom). These data are derived from thermogravimetry in flowing (100, 21, 2, 1, and 0.091% ) O sub 2 at atmospheric pressure. Other supporting thermoanalytical data, DSC, DTA, and EGA are presented to further help understand the effects of atmosphere in this system. For example, the melting point of Ba sub 2 YCu sub 3 O sub x as determined from DTA at 20C min sup (-1) was found to vary from approximately 975C in N sub 2 to about 1035C in O sub 2.