Control of the in-plane epitaxy for bi-epitaxial grain boundary junctions using a new multilayer structure

In order to obtain 100% bi-epitaxial 45°grain boundary junctions of YBa₂Cu₃O_x (YBCO), we have systematically examined the in-plane epitaxy of CeO₂ films grown on MgO substrates. The inevitable presence of CeO₂[110]∥MgO[100] causes mixtures of in-plane rotation of 0°and 45°between YBCO/CeO₂/MgO and YBCO/MgO. We have further developed a new structure, namely YBCO/CeO ₂/Yttria-stabilized ZrO₂/MgO and YBCO/MgO boundary, so that 100% in-plane rotation of 45°can be routinely obtained. The model of the in-plane epitaxial relationship between the multilayers using near coincident site lattices was proposed. The critical current density of the junctions made on the boundary is 3×10³ A/cm² at 77 K, while the order of the J_c of YBCO films on both sides of the grain boundary is 10⁶ A/cm². The current-voltage characteristics of the junctions show resistively shunted junction behavior. The better epitaxy of our new structure can lead to a better control of grain boundary critical current density.