EuBa₂Cu₃O_7-δ Thin Films Grown on Sapphires with Epitaxial CeO₂ Buffer Layers

Abstract

Epitaxial growth of CeO 2 films on Al 2 O 3 (11̄02) substrates and the effect of CeO 2 buffer layers on the growth orientation and superconducting properties of EuBa 2 Cu 3 O 7-δ (EBCO) were investigated. CeO 2 and EBCO films were prepared by rf and dc magnetron sputtering, respectively, and were characterized by X-ray diffraction (θ-2θ scan and ϕ scan), atomic force microscopy (AFM) and high resolution scanning electron microscopy. Epitaxial (001) CeO 2 films were obtained at an off-center distance ( D on-off ) of 3.5 cm and a substrate temperature of 660°C. The structural and superconducting properties of EBCO films deposited at 650°C depended on the thickness of the CeO 2 buffer layer. The EBCO films deposited on CeO 2 50-400-Å-thick buffer layers had T ce 's of 90 K or above. The high- T c EBCO films had in-plane epitaxial orientation relationships of Al 2 O 3 [112̄0]\varparallelCeO 2 [100]\varparallelEBCO[110]. The EBCO films on the thin CeO 2 buffer layers had rectangular grains similar to those on MgO(001) substrates. The critical current density of the EBCO films with T ce =90 K was about 6 ×10 5 A/cm 2 in zero field at 77.3 K. The T ce varied largely and decreased with increasing CeO 2 buffer layer thickness above 500 Å. AFM observation of a 1000-Å-thick CeO 2 film showed growth of bamboo-like crystal grains 1700 Å long and 300 Å wide along the direction of CeO 2 [110]. The ravine depths were about 100 Å. The EBCO films on the thick CeO 2 buffer layer (>500 Å) exhibited poor superconducting behavior and gave (103) or (110) diffraction peaks.