The interfaces in YBa₂Cu₃O₇/BaTbO₃ and PrBa₂Cu₃O₇/BaTbO₃ heterostructure thin films

The interfaces in YBa₂Cu₃O₇/BaTbO₃ and PrBa₂Cu₃O₇/BaTbO₃ heterostructure thin films are investigated by high-resolution transmission electron microscopy. Depending on the deposition temperature of the BaTbO₃ layers two types of interface, type I and type II, are found. For a deposition temperature of 780_°C the interfaces between YBa₂Cu₃O₇and BaTbO₃ are of type I. In this configuration a Cu-O chain plane of YBa₂Cu₃O₇or PrBa₂Cu₃O₇faces a TbO₂ plane of BaTbO₃Interface dislocations are found whose line direction is [110] or [110]. Residual misfit can be observed in a layer close to the interface. At a deposition temperature of 500_°C, type I and type II interfaces coexist. In the type II configuration, a Cu-O plane of YBa₂Cu₃O₇or rBa₂Cu₃O₇ faces a BaO plane of the BaTbO₃ layer. In this case, misfit dislocations are found to lie along the [100] and [010] directions. In addition, close to the interface the lattice is strongly distorted. Models for the interface structure are suggested and tested by image simulation. The differences in dislocation configuration and residual strain level for the two types of interface are discussed in the light of O-lattice theory and the bonding state of the ions in the interface layer.