Chemical interaction between Ba2YCu3O6+x and CeO2 at pO2=100Pa

Chemical interaction between the Ba2YCu3O6+x superconductor and the CeO2 buffer layers employed in coated conductor architectures has been modeled experimentally by investigating phase equilibria on the Ba2YCu3O6+xCeO2 join at pO2=100Pa. This join is actually a non-binary join within the BaOY2O3CeO2CuOx quaternary system. At an approximate mole ratio of Ba2YCu3O6+x : CeO2 = 40 : 60, a phase boundary was found to separate two four-phase regions. At the Ba2YCu3O6+x-rich side of the join, the four-phase region consists of Ba2YCu3O6+x, Ba(Ce1−zYz)O3−x, BaY2CuO5, and Cu2O; at the CeO2 rich side, the four phases were determined to be Ba(Ce1−zYz)O3−x, BaY2CuO5, Cu2O and CeO2. At 810 °C and pO2=100Pa, there appears to be negligible solid solution formation of the types Y1−zCezO3−x and Ce1−zYzO2−x. The minimum melting temperature along the Ba2YCu3O6+xCeO2 join was determined to be ≈860 °C. As part of this study, phase diagrams of the subsystems CeO2Y2O3CuOx, BaOCeO2CuOx, and BaOY2O3CeO2 were also determined at 810 °C under 100 Pa pO2. The Y2O3CeO2CuOx diagram does not contain ternary phases and shows a tie-line from Y2O3 to the binary phase Y2Cu2O5−x. Similarly, the BaOCeO2CuOx diagram contains no ternary phases, but has four tie-lines originating from BaCeO3 to Ba2CuO3+x, BaCuO2+x, BaCu2O2+x and CuOx. The BaOY2O3CeO2 system contains one ternary phase, the solid solution Ba(Ce1−zYz)O3−x (0⩽z⩽0.13), which crystallizes with the orthorhombic space group Pmcn (No. 62). Neutron Rietveld refinement of Ba(Ce0.94Y0.06)O2.84[Ba(Ce3+0.26Ce4+0.68Y0.06)O2.84] gives lattice parameters of a=8.7817(4)Å, b=6.2360(4)Å, c=6.2190(3)Å, V=340.57Å3, Z=4. The structure consists of distorted corner-shared (Ce,Y)O6 octahedra that are tilted with respect to each other. Ba was found to have 9 nearest neighbors (distances < 3.5 Å). Reference X-ray patterns of Ba(Ce0.90Y0.10)O2.95 and Ba(Ce0.87Y0.13)O2.93 were submitted to be included in the Powder Diffraction File (PDF).