Kinetic studies of the interfacial reaction of the Ba2YCu3O6+x superconductor with a CeO2 buffer

Interfacial reactions between the Ba2YCu3O6+x superconductor and the CeO2 buffer layers employed in coated conductors have been modeled experimentally by investigating the kinetics of the reaction between Ba2YCu3O6+x films and CeO2 substrates. At 810°C, the Ba2YCu3O6+x -CeO2 join within the BaO-Y2O3-CeO2-CuO x quaternary system is nonbinary, thereby establishing the phase diagram topology that governs the Ba2YCu3O6+x /CeO2 reaction. At a mole ratio of Ba2YCu3O6+x :CeO2 of 40:60, a phase boundary was found to separate two four-phase regions. On the Ba2YCu3O6+x -rich side of the join, the four-phase region consists of Ba2YCu3O6 +x , Ba(Ce1−z Y z )O3−x , BaY2CuO5, and CuO x ; on the CeO2 rich side, the four phases were determined to be Ba(Ce1−z Y z ) O3−x , BaY2CuO5, CuO x and CeO2. The Ba2YCu3O6+x /CeO2 reaction is limited by solid-state diffusion, and the reaction kinetics obey the parabolic rule, x = Kt 1/2, where x = thickness of the reaction layer, t = time, and K = a constant related to the rate constant; K was determined to be 1.6 × 10−3 μm/s1/2 at 790°C and 4.7 × 10−3 μm/s1/2 at 830°C. The activation energy for the reaction was determined to be E act = 2.67 × 105 J/mol using the Arrhenius equation.