Superconducting Properties and Microstructures of BaHfO₃-doped SmBa₂Cu₃O_y Films Fabricated using a Low-temperature Growth Technique

Abstract

We have proposed a low-temperature growth (LTG) technique which makes it possible to fabricate SmBa₂Cu₃O_y (SmBCO) films with c-axis orientation in a wide range of growth temperatures without the degradation of superconducting properties. In this study, using the LTG technique, we fabricated SmBa₂Cu₃O_y (SmBCO) films with BaHfO₃ (BHO) nano-rods at low substrate temperatures using the pulsed laser deposition (PLD) method. The effect of low substrate temperatures on BHO nano-rods in SmBCO films are discussed in terms of their microstructures and superconducting properties. The nano-rods were observed clearly in transmission electron microscopic (TEM) images of the films. We found that the morphologies of the nanorods were small in diameter, had high densities and inclined along the c-axis of SmBCO. In the case of the substrate temperature of 750^°C, the diameter and density of nano-rods with 2.7 vol.% BHO-doping were 5.7 nm and 2300 /μm², respectively. The film showed high flux pinning force, F_p, of 25 GN/m³ (77 K, B//c) in a high field, 4 T. Furthermore, in the film, the angular dependence of J_c showed a broad peak at B//c, due to the flux pinning by nano-rods growing in various directions.