Subsolidus phase relationships of the BaO-R2O3-CuOz (R = Tm and Yb) systems under carbonate-free conditions at pO2 = 100 Pa, and T = 750 °C and 810 °C

For applications of phase equilibria to coated conductor processing, phase diagrams constructed under carbonate-free conditions should be employed. Using special apparatus and a procedure for preparing carbonate-free precursors based on BaO, phase diagrams of the BaO-Tm2O3-CuOz and BaO-Yb2O3-CuOz systems were determined at 100 Pa (0.1% O2 by volume, 750 °C and 810 °C). The BaO-Yb2O3-CuOz system exhibits different features as compared to the Tm-analog. For example, the Yb-system does not contain the Ba4RCu3O8.5+z phase. The absence of this phase affects the tie-line relations in the BaO-rich region of the phase diagram of the Yb-system. Furthermore, while the diagrams with relatively large R (i.e., R = Nd, Sm, Eu, Gd, Dy, Er) do not contain a tie-line between BaCuO2+z and BaR2CuO5, this tie-line was found in the Yb-diagram, which has a much smaller R. In general, both the diagrams of the BaO-Tm2O3-CuOz and of the BaO-Yb2O3-CuOz systems prepared under carbonate-free conditions are different from those obtained using BaCO3-derived starting materials.