We have determined the stability line in the 1/T−log[P(O2)] phase space for the synthesis of Nd1+xBa2−xCu3Oy (NdBCO) films. A systematic study of Tc, Jc, and ρ(T) dependence on oxygen partial pressure and temperature for the deposition of thin NdBCO films grown by pulsed-laser deposition was performed. The conditions for optimal NdBCO film growth were determined by varying oxygen partial pressure from 0.02 to 400 mTorr, and substrate temperature between 730 and 800 °C. The results show that the best NdBCO films are obtained at oxygen pressures in the range of 0.2–1.2 mTorr, depending on the substrate temperature. This is more than two orders-of-magnitude lower than the correspondent oxygen pressure appropriate for YBa2Cu3O7−δ film growth.

Epitaxial YBa2Cu3O7−x (YBCO) films with critical current densities exceeding 1 MA cm−2 (at 77 K in self magnetic field) were epitaxially grown on biaxially textured Ni 5 at% W (Ni–W) substrate using only a CeO2 buffer layer. Both YBCO and CeO2 films were deposited in situ by pulsed laser ablation. The oxidation behaviour of the Ni–W substrate enables the epitaxial growth of a CeO2 oxide buffer layer without using the forming gas (Ar 4%H2). SEM investigations of YBCO and CeO2 films reveal a dense microstructure without cracks or porosity. X-ray pole figures show a cube-on-cube epitaxy with a [100]YBCO//[110]CeO2//[100]Ni–W epitaxial relationship. The YBCO superconducting film has a good out-of-plane and in-plane texture with a full-width-half-maximum of 5.8° and 6.6°, respectively. No severe degradation of JC with film thickness, up to 1 μm thick films, was observed. The use of a single buffer layer on Ni–W substrates represents an important simplification in the scaling-up for long tape fabrication.

No abstract

A morphological study of on-axis NdBa2Cu3O7-δ (NBCO) and on-axis and off-axis YBa2Cu3O7-δ (YBCO) pulsed laser deposited films is presented. YBCO films deposited in on-axis geometry exhibit a high droplet density of about 107 cm-2 and three-dimensional features probably related to stoichiometric outgrowths. YBCO off-axis films present a surface with very low droplet density (about 105 cm-2) and the density of other defects like holes and stoichiometric outgrowths is less than 103 cm-2. In spite of a higher droplet density with respect to off-axis YBCO (about 106 cm-2), NBCO films have a surface without other defects. Moreover, the NBCO film morphology is almost insensitive to variation in the deposition conditions. Atomic force microscopy analysis revealed that YBCO off-axis deposited films grow in a spiral growth mode, while NBCO films exhibit a texture, probably due to an initial two-dimensional growth. The YBCO off-axis and NBCO films have a mean roughness in a 10×10 µm2 area of about 7.5 and 1.45 nm, respectively.

No abstract