The phase diagrams of the BaOGd 2 O 3 CuO z and BaOEr 2 O 3 CuO z systems were determined at 100 Pa (0.1% O 2 by volume, 810 °C) by using special apparatus and a procedure for preparing carbonate-free precursors based on BaO. The diagram of the BaOEr 2 O 3 CuO z system was confirmed to be similar to that of the Y-analog. The diagram of the BaOGd 2 O 3 CuO z system exhibits different features as compared to the Er-analog. While the Er-system includes the Er 2 Cu 2 O 5 phase, the Gd-system involves the Gd 2 CuO 4 phase instead. The absence of the Ba 3 R 4 O 9 phase in the Gd-system affects the tie-line relations in the region bounded by BaO, BaGd 2 O 4 , BaGd 2 CuO 5 and Ba 6 GdCu 3 O z . In general, both the diagrams of the BaOEr 2 O 3 CuO z and of the BaOGd 2 O 3 CuO z systems prepared under carbonate-free conditions are different from those obtained using BaCO 3 -derived starting materials. For applications of phase equilibria to coated conductor processing, phase diagrams constructed under carbonate-free conditions should be employed.