Characterization of YbBa2Cu3O7—y Superconducting Thin Films Prepared by Chemical Solution Deposition on SrTiO3 (001) and LaAlO3 (001) Substrates

Abstract

c‐axis oriented films of YbBa2Cu3O7—y have been prepared by postdeposition annealing of metal (Yb, Ba, Cu) naphthenate gels spin‐coated on SrTiO3 (001) and LaAlO3 (001) substrates in the temperature range from 650 to 900 °C under oxygen partial pressures from about 105 to 10 Pa. High resolution electron microscopy studies showed that the thickness of the as‐prepared c‐axis YbBCO films was in the range from 80 to 100 nm after postdeposition annealing at 725 °C for the film on SrTiO3 and at 750 °C for the film on LaAlO3; above this thickness, a small amount of Yb2O3, CuO, and random‐oriented Yb123 phases were observed. The c‐axis film obtained on the SrTiO3 (001) substrate is defective with stacking faults to form a defect microstructure rather than forming the well‐ordered YbBa2Cu4O8 (Yb124) phase. The film obtained on the LaAlO3 (001) substrate, in contrast to that on SrTiO3, involves a small amount of a‐axis Yb123 grains with dimensions of 5 to 30 nm. The Tc,zero value is 89 K for the film derived on SrTiO3 and 85.5 K for the film on LaAlO3.

RE BCO mixtures with large difference in rare-earth ion size: superconducting properties of chemical solution deposition-grown Yb 1− x Sm x Ba 2 Cu 3 O 7− δ films

“…The T c values, figure 2, vary between approximately 90.5 K for the pure YbBCO films and approximately 95 K for the pure SmBCO films. These values are similar to the ones reported in previous works for YbBCO [13][14][15][16][17][18] and SmBCO films [12,[34][35][36] prepared by different techniques and also resemble previously reported values for YbSmBCO bulk samples [33]. The influence of Yb content on T c is very remarkable.…”

“…J sf c at 77 K varies between approximately 1 MA cm −2 for pure YbBCO and approximately 2 MA cm −2 for pure SmBCO with the films with x = 0.5 and x = 0.9 in between. Although these values seem to be quite modest, they are among the largest published for YbBCO [13][14][15][16][17][18] and also SmBCO films [12,[34][35][36] grown by different techniques. However, at lower temperatures, the mixed films start to compete with the pure phases.…”

“…Recently, our group has been able to prepare SmBCO films by chemical route showing the difficulties associated with the tendency of Sm 3+ ions to occupy the Ba 2+ sites [12]. Also, several works reported the problems in preparing YbBCO films, leading, in general, to quite modest maximum critical temperatures T c ∼ 90 K and self-field critical current densities, J c sf , at 77 K of approximately 1 MA cm −2 [13][14][15][16][17][18]. Another approach, and probably the most important one, for improving the superconducting properties of REBCO films is to increase the flux pinning.…”