Sputtered and reactively grown epitaxial GdAlO{sub 3} films as buffer layers for c-oriented YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} films on R-sapphire

Thin films of the orthorhombic perovskite GdAlO{sub 3} were grown on R-plane sapphire single crystals. Two different film growth methods were used, viz. (i) a chemical reaction of a Gd-O plasma with the sapphire crystals, and (ii) the reactive radio frequency (r.f.) sputtering of a GdAlO{sub 3} target. Subsequently, YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) films were deposited onto the GdAlO{sub 3} buffer by pulsed laser deposition (PLD). The GdAlO{sub 3} and YBCO films were investigated by X-ray diffraction pole figure analysis and transmission electron microscopy (TEM), including high-resolution transmission electron microscopy of cross sections. Independent of the deposition method the GdAlO{sub 3} films grew according to the nearly equivalent orientation relationships (110){sub perovskite} {parallel} (1{bar 1}.2){sub sapphire}; [111] or [11{bar 1}]{sub perovskite} {parallel} [11.0]{sub sapphire} and (002){sub perovskite} {parallel} (1{bar 1}.2){sub sapphire}; [100] or [010]{sub perovskite} {parallel} [11.0]{sub sapphire}. The GdAlO{sub 3} grains are additionally tilted by angles up to {+-}3{degree} around the sapphire [{bar 1}1.1] axis. On top of these buffer layers the YBCO films grew with c-orientation and with an in-plane rotation of 45{degree}. YBCO films of 200 nm thickness on GdAlO{sub 3} buffer layers with a thickness of 10 to 20 nm showed a {Tc} > 87more » K and a j{sub c}(77 K) > 3 {times} 10{sup 6} A/cm{sup 2}.« less