The microstructure of continuously processed YBa₂Cu₃O_y coated conductors with underlying CeO₂ and ion-beam-assisted yttria-stabilized zirconia buffer layers

The microstructural development of YBa₂Cu₃O_y (Y-123) coated conductors based on the ion-beam-assisted deposition (IBAD) of yttria-stabilized zirconia (YSZ) to produce a biaxially textured template is presented. The architecture of the conductors was Y-123/CeO₂/IBAD YSZ/Inconel 625. A continuous and passivating Cr₂O₃ layer forms between the YSZ layer and the Inconel substrate. CeO₂ and Y-123 are closely lattice-matched, and misfit strain is accommodated at the YSZ/CeO₂ interface. Localized reactions between the Y-123 film and the CeO₂ buffer layer result in the formation of BaCeO₃, YCuO₂, and CuO. The positive volume change that occurs from the interfaCial reaction may act as a kinetic barrier that limits the extent of the reaction. Excess copper and yttrium generated by the interfacial reaction appear to diffuse along grain boundaries and intercalate into Y-123 grains as single layers of the Y-247, Y-248, or Y-224 phases. The interracial reactions do not preclude the attainment of high critical currents (I_c) and current densities (J_c) in these films nor do they affect to any appreciable extent the nucleation and alignment of the Y-123 film.