Activity and diffusivity of oxygen in liquid Ag-Yb1Ba2Cu3 and Tl1Ba2Ca2Cu3 alloys

Abstract

We have measured the activity and diffusivity of oxygen in liquid Ag-Yb1Ba2Cu3 and Tl1Ba2Ca2Cu3 at 930 and 900 °C, respectively, by a modified coulometric titration method on the galvanic cell: O_ in liquid alloys/yttria stabilized zirconia/air, Pt. The standard Gibbs formation energy and the diffusivity of oxygen in liquid Ag-Yb1Ba2Cu3 alloy for 1/2O2(1 atm)→O_(1 at. %) are determined to be ΔG=−247.4 kJ/g atom, and D=1.52×10−4 cm2/s. The oxygen solubility Cs in the Ag-Yb1Ba2Cu3 alloy is 0.0913 at. %, a factor of 5.5 higher than that in Yb1Ba2Cu3 alloy. The addition of Ag does not alter the growth mechanism and the oxygen diffusion controls the film growth. The growth speed is enhanced as a result of the enhanced oxygen solubility. ΔG and the diffusion coefficient of oxygen in the Tl1Ba2Ca2Cu3 liquid alloy are −257 kJ/g atom and 1.2×10−4 cm2/s, respectively. The oxygen solubility of the Tl1Ba2Ca2Cu3 alloy at 900 °C is found to be very high at ∼5.74 at. %. All thermodynamic data for oxygen in the precursor alloys are consistent with each other but there is a deviation of activity coefficient with composition for the different alloys from the theoretical model.