c-Oriented YBa₂Cu₃O_7−δ film with embedded a-oriented grains grown by liquid phase epitaxy under fine-tuning supersaturation

Abstract

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.

Evolution of Oriented Structures in YBa2Cu3O7−δ Films by Liquid Phase Epitaxy through Manipulating Supersaturation

“…The colored areas show the solution state alternation from one unsaturated state to its corresponding supersaturated state through a rapid temperature decline from T m to T g . When Δ t m was fixed to 2.5 h, when Δ m was adjusted to be nearly 15 g, the solution state U low transforms to U mid 0 a / c (for σ mid 0 a / c ), as exhibited in the inset of Figure b. In order to gain U mid 0+90 a / c (for σ mid 0+90 a / c ), more of Y 3+ ion solute should join the solution, which involves their dissolution from the Y 2 O 3 crucible and diffusion through the solution.…”

“…Additionally, the XRD patterns in Figure a,b exhibit the typical peaks of ( h 00) and (00 l ), displaying features of the a- and c -films, respectively. Next, the c -film with epitaxial a -grains was grown by a fine-tuning technique . First, a holding time of Δ t h = 12 h was employed to adjust the solution state to a close to equilibrium state (termed M init ) at the initial melting stage.…”

“…Apart from the two extreme supersaturated states, σ low and σ high , there is the midway σ mid calue (the same as σ int in ref 24) in the R ∼ σ curve, which corresponds to the composite epitaxial microstructures: e.g., the c-film with the a-grains. In order to obtain σ mid , Xiang et al 24 extended the unsaturatedto-supersaturated approach 24 by a fine-tuning technique. In detail, the holding time (Δt h ) of solution before addition of SSM, the third controlling factor, was induced to change the initially uncertain state to a certain one.…”

“…Next, the c-film with epitaxial a-grains was grown by a fine-tuning technique. 24 First, a holding time of Δt h = 12 h was employed to adjust the solution state to a close to equilibrium state (termed M init ) at the initial melting stage. Then, with Δt m = 2.5 h fixed, a Δm value of 15 g was used to gain an intermediate level for unsaturated solution (U mid ) at the unsaturated midway stage.…”

“…Apart from the two extreme supersaturated states, σ low and σ high , there is the midway σ mid calue (the same as σ int in ref ) in the R ∼ σ curve, which corresponds to the composite epitaxial microstructures: e.g., the c -film with the a -grains. In order to obtain σ mid , Xiang et al extended the unsaturated-to-supersaturated approach by a fine-tuning technique. In detail, the holding time (Δ t h ) of solution before addition of SSM, the third controlling factor, was induced to change the initially uncertain state to a certain one.…”