c-Oriented YBa2Cu3O7−δ film with embedded a-oriented grains grown by liquid phase epitaxy under fine-tuning supersaturation

The performance of superconductor films is related to their crystallographic orientations, which are strongly dependent on the supersaturation (σ) in the solution used for liquid phase epitaxy (LPE). To date, except for two extreme states, low and high σ for the preparation of a- and c-axis-oriented YBa2Cu3O7−δ films, respectively, little attention has been directed toward intermediate σ, which is of great importance for achieving a variety of artificial microstructures that are in principle difficult to obtain by existing crystal growth methods. Here, a further step is taken towards the comprehension of how the crystallographic orientations and microstructure are correlated with supersaturation. Fine-tuning of σ to an intermediate state is realized by introducing an additional factor, namely the holding time, that adjusts the initially uncertain state to a certain and stable one. This factor is controlled along with the commonly used variables of the amount of fresh solvent material and the melting time. Consequently, for the first time, a composite epitaxial microstructure of a c-axis-oriented YBa2Cu3O7−δ film with embedded a-axis grains on a (110) NdGaO3 substrate was successfully grown by LPE. The epitaxial interface between a- and c-axis grains potentially serves as a flux pinning site. This work provides further insights into how control of artificial microstructures can be used to enhance superconducting properties.