Orientation mechanism of liquid phase epitaxial grown YBa₂Cu₃O_7-y film

Abstract

Superconducting YBa₂Cu₃O_y films were grown by liquid-phase epitaxy (LPE) on NdGaO₃(l10) single-crystalline substrate by a modified top-seeded crystal growth method. Two different melt compositions were used. In the case of Cu-poor melt composition (Ba:Cu=3.0:5.0), only c-axis oriented growth was observed. However, if we used Cu-rich melt composition (Ba:Cu=3.0:6.5), both c-axis and a-axis oriented films were obtained. In the latter case the crystalline orientation of YBa₂Cu₃O_y films was dependent on the temperature of the surface of the melt. At lower temperatures, c-axis orientation films were obtained, whereas the films showed a-axis orientation at higher temperatures. The width of transition temperature range of orientation is very narrow, less than 3 °C, compared to the width observed in the conventional vapor phase depositions (which is typically 50 °C). We propose that orientation change in the liquid phase epitaxial growth is determined by the unique properties of the phase diagram of Y-Ba-Cu-O-system.