Influence of oxygen partial pressure on the kinetics of YBa₂Cu₃O_7−x formation

The YBa₂Cu₃O_7−x formation kinetics from a spray-roasted precursor powder containing Y₂O₃, BaCO₃, and CuO was followed via in situ, time-resolved x-ray diffraction as a function of gas atmosphere and temperature. In inert atmospheres, BaCO₃ and CuO form BaCu₂O₂ which subsequently reacts with Y₂O₃ to form YBa₂Cu₃O₆. However, YBa₂Cu₃O₆ decomposes at temperatures exceeding 725 °C with Y₂BaCuO₅ being one of the decomposition products. In oxidizing atmospheres, YBa₂Cu₃O_7−x formation involves the BaCuO₂. At high temperatures (800–840 °C), oxygen increases the yield of YBa₂Cu₃O₆. A nuclei growth model assuming two-dimensional, diffusion-controlled growth with second-order nucleation rate fits the experimental data.