Supersaturation-Controlled Growth Orientation and Grain Boundary Transition in REBa₂Cu₃O_7−δ (RE = Sm, Sm_1−xY_x) Liquid-Phase Epitaxial Films

Abstract

Different kinds of REBa2Cu3O7−δ (RE = Sm, Sm−Y mixture) a/c grain boundaries are obtained by altering growth parameters such as temperature or oxygen partial pressure. We attribute the boundary structure variation to the a/c grain growth competition, which mainly depends on the supersaturation in the melt. A fine a/c boundary structure is obtained under certain growth conditions. The diffusion time, for which the growth atoms can stay on the growth interface, is considered as a unique kinetic limit in the growth orientation transition mechanism in the liquid-phase epitaxy (LPE) process. The growth mechanism is suggested as a combined effect of thermodynamic and kinetic factors.

Growth condition related orientation transition for YBa2Cu3O7−δ films on NdGaO3 substrate

“…It is well known that the growth rate of YBCO is different between the a-axis and the c-axis in the case of crystal growth. However, it was already reported that in LPE experiment, the growth rates of the a-axis and the c-axis oriented YBCO change with supersaturation [8,22]. As a result, the same height of the two phases implies that the growth rates of two kinds of grains are comparable.…”

“…7 displays a relationship between the film orientation and the effective s, which depends on the solute diffusion, the etch-back effect, and the growth temperature. Generally, supersaturation of solution increases as the temperature decreases, with an identical cooling rate, below the T p of the system [16,22,27]. More precisely, since in our dipping experiment, the epitaxy happens as soon as the temperature reaches the growth temperature, that is, a nonequilibrium state.…”

“…On the other hand, from the growth kinetics point of view, to reach the appropriate crystal lattice site, the atoms need to move along much longer migration distance in the c-axis growth than in the a-axis growth. Thus the average time of atoms diffusion in the a-axis growth is shorter than that of the c-axis growth [22,26]. As a result, the higher energy barrier for growth of c-oriented film is requested, that is, larger diving force is needed for the c-axis growth.…”

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

“…In addition, c-films with a variety of epitaxial nanoparticles as sources of flux pinning (Haugan et al, 2004;MacManus-Driscoll et al, 2004;Gutié rrez et al, 2007;Abellá n et al, 2011) have been widely produced by various deposition methods, greatly enhancing the critical current density (J c ). For the latter, a similar construction, a c-film with epitaxially grown a-axis-oriented grains, was grown by liquid phase epitaxy (LPE) (Tang et al, 2010). However, such a composite epitaxial structure cannot be reliably and repeatably achieved, because its formation is strictly limited to a narrow supersaturation range in the solution, near the a/c orientation transition point, where the growth rate in the c-axis direction is slightly higher than that in the a-axis direction.…”

Structural study of epitaxial NdBa2Cu3O7−x films by laser chemical vapor deposition

“…[4][5][6] For NdBCO crystal, critical current along the ab-plane is far superior to that along the c-axis, because of the difference between the coherent length (x) along the ab-plane (1.5-2 nm) and the c-axis (0.2-0.3 nm) of NdBCO. 7 Therefore, c-axisoriented and well ab-aligned NdBCO lm possesses highranking superconducting properties. As a matter of fact, caxis-oriented epitaxial growth of NdBCO lms has been studied under the cases of various fabrication techniques, including metal organic chemical vapor deposition (MOCVD), 8,9 pulsed laser deposition (PLD), 10,11 magnetron sputtering.…”