Dominant Effect of Oxygen Enhancement on the Crystalline Orientation of YBa₂Cu₃O_x Film Prepared by Liquid-Phase Epitaxial Growth

Abstract

A pure oxygen atmosphere during liquid-phase epitaxial (LPE) growth of YBa2Cu3O x (YBCO) significantly affected the crystalline orientation of the grown films. In the previous investigation, only the c-axis-oriented YBCO film can be obtained from the melt with a 3.0:5.0 Ba:Cu ratio under a typical air atmosphere. However, in our present study, it was found that high-quality a-axis-oriented films readily grew from the flux with a 3.0:5.0 Ba:Cu ratio when the atmosphere was changed to pure oxygen. Furthermore, the growth “window” of a-axis films was obviously enlarged compared with experimental results in the air atmosphere. On the basis of the “surface migration” theory, we elucidate the origin of a-axis growth promotion by a suppression of the migration ability of the growth species in the melt with increasing content of oxygen.

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

“…Obviously, the effective s values in O 2 and in air are equal at this transition temperature. In short, the mechanism combining supersaturation with the effect of etch-back and solute diffusion gives an integrated interpretation of the out-of-plane orientation transition, in accordance with our present work as well as with previous works [3][4][5][6][7][8][9][10][11][12][13][14].…”

“…On the other hand, because of the enormous crystallographic anisotropy and the complicated atomic structure, the preparation of REBCO films with the specific orientation is really difficult. However, aiming at clarification of the mechanism of the phase transition, there is large amount of the studies associated with thin film orientation-control growth in both vapor phase epitaxy (VPE) and liquid phase epitaxy (LPE) [3][4][5][6][7][8][9][10][11][12][13][14].…”

“…Based on the surface energy estimation, the thermal migration was suggested as the leading mechanism which affects the film orientation, but the phenomenon of the double transition has not been well interpreted yet. For the LPE growth of YBCO films, the influence of growth conditions on out-of-plane orientation has been widely studied, as illustrated in Table 1 [4][5][6][7][8][9][10][11][12]. Some of the groups reported the a-c-a-axis transition with decreasing growth temperature for both the temperature regions, above the peritectic temperature (T p ) and below T p , that is inconsistent with occurrence of the a-caxis transition in a lower temperature range, below T p , reported by the others.…”

“…Summary of the literature results on the out-of-plane orientation transition[4][5][6][7][8][9][10][11][12].…”

YBa2Cu3Oyliquid-phase epitaxy films ofaorientation grown under ultra-low supersaturation caused by a homogeneous nucleation catastrophe

“…An enhanced oxygen environment has been effectively used to prepare pure a-films (Cai et al, 2007); nevertheless, this growth condition results in a complicated experimental system. Meanwhile, extensive studies (Kitamura et al, 1995;Cai et al, 2006;Chen et al, 2012) proved that it is hard to obtain a pure a-film in ambient air (a temperature range of less than 3 K in a Cu-rich melt; Kitamura et al, 1995;Cai et al, 2006).…”