Microstructural and superconducting properties of (Y_1−<i>x</i>Eu_<i>x</i>)Ba₂Cu₃O_7−δthin films:<i>x</i>= 0–1

Abstract

Thin films of (Y1?xEux)Ba2Cu3O7?? with x = 0?1 were grown by pulsed laser deposition on single crystal substrates, to determine the effect of Y and Eu substitution on the microstructural and superconducting properties. The film critical transition temperature (Tc), critical current density (Jc) and surface roughness were found to be strongly dependent on the substrate choice, with the best properties achieved on CeO2?YSZ substrates. Substrates with varying lattice mismatch from ?2% to +1% were studied, including LaAlO3, SrTiO3, CeO2-buffer-coated Zr0.905Y0.095O2 (YSZ), and (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT). With increasing Eu substitution from x = 0 to 1, the Tc on CeO2?YSZ substrates increased steadily from 89 to 93?K. The value of Jc was measured by magnetic methods at 65 and 77?K, and by transport methods at 77?K for selected samples and different angles of orientation Happl(?) = 0??90?. As Eu substitution was increased from x = 0 to ???0.2, Jc at 77?K increased strongly more than two-fold for ?T and for H<0.5?T for all orientations 0????90?; but, it decreased more than two-fold for ?T. The Jc(H) properties at both low and high fields correlated well with microstructural features observed by scanning electron microscopy. The low-field was enhanced when the grain size was reduced to ~100?nm size, and the self-field and high-field Jc(H) appeared to be strongly affected by the film density and porosity. A controlled dense-island structure was noted for x = 0.75, on CeO2?YSZ substrate.