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The interface between yttria-stabilized zirconia (YSZ) substrate and YBa₂Cu₃O₇ (YBCO) film was studied by high-resolution electron microscopy. In all specimens we have observed an intermediate layer of BaZrO₃ located between the substrate YSZ and YBCO. The BaZrO₃ layer is composed of almost equally aligned domains being 4–8 nm in the lateral directions. Reaction products such as Y and Cu oxides were never observed in or close to the BaZrO₃ reaction layer but they do occur in the YBCO film. The stacking sequence of BaZrO₃/YBCO is predominantly (BaZrO₃)-ZrO₂-BaO/CuO-BaO-(YBCO) with CuO layer as the beginning YBCO layer. Sometimes a stacking sequence (BaZrO₃)-ZrO₂-BaO/BaO-CuO₂-(YBCO) with a BaO layer as the beginning YBCO layer was observed. This stacking is related to a dislocation with Burgers vector a'/2 [111], where a' = 0.42 nm is the lattice constant of the cubic BaZrO₃ …