Engineered oxide thin films as 100% lattice match buffer layers for YBCO coated conductors

Abstract

One of the most important qualities of buffer layers for RE-BCO coated conductors' growth is close lattice match with RE-BCO. However, there is no natural material with a 100% lattice match with RE-BCO. In this study mixtures of europium oxide (Eu2O3) and ytterbium oxide (Yb 2O3), (Eu1-uYbu)2O 3 (0.0≤u≤1.0), were investigated as a candidate buffer layer that could have same lattice parameter as YBa2Cu3O 7-δ(YBCO). Because the pseudocubic lattice parameter of Eu 2O3 is bigger, and that of Yb2O3 is smaller than lattice parameter of YBCO, and the mixed oxides with appropriate ratio would have same lattice parameter of YBCO. The mixtures were prepared using metal-organic precursor by sol-gel process, and it was found that all mixed samples are single phase, complete solid solutions, and have same crystal system over the whole range of "u". Lattice parameters of mixed (Eu1-uYbu)2O3 oxide powders were changed between 10.86831 and 10.42828 Å which are lattice parameter of Eu2O3 and Yb2O3, respectively by changing the ratio of Eu/Yb in the mixture. Phase and lattice parameter analysis revealed that pseudocubic lattice parameter of (Eu 0.893Yb0.107)2O3 is 3.82 Å which is same as the lattice parameter of YBCO. Textured (Eu 0.893Yb0.107)2O3 buffer layers were grown on biaxially textured-Ni (100) substrates. The solution was prepared from Europium and Ytterbium 2,4-pentadioanate, and was deposited on the Ni substrates using a reel-to-reel sol-gel dip coating system. The textured films were annealed at 1150 °C for 10 min under 4% H2-Ar gas flow. Extensive texture analysis has been done to characterize the texture of (Eu 0.893Yb0.107)2O3 buffer layers. X-ray diffraction (XRD) of the buffer layer showed strong out-of-plane orientation on Ni tape. The (Eu0.893Yb0.107) 2O3 (222) pole figure indicated a single cube-on-cube textured structure. The omega and phi scans revealed good out-of-plane and in-plane alignments. The full-width-at-half-maximum (FWHM) values of omega and Phi scan of (Eu0.893Yb0.107)2O3 films were 6.45° and 7.70°, respectively. ESEM micrographs of the films revealed pinhole-free, crack-free and dense microstructures. © 2003 Elsevier Ltd. All rights reserved.