J_c characteristics in high magnetic field of RE _1-xBa_2-xCu₃O_6-y films prepared by pulsed laser deposition

We have investigated the superconducting properties and the microstructure of the c-axis oriented Sm_1-xBa_2-xCu₃O _6-y(Sm-123) and GdBa₂Cu₃O_6-y(Gd-123) thin films deposited on MgO substrates deposited by pulsed laser deposition (PLD). From their J_c-B characteristics, it has been observed that the superconducting properties of Sm-123 (x = 0), Sm-123 (x = 0.08) and Gd-123 are superior to those of the YBa₂Cu₃O_7-y thin films for B//c, 5 T at 77 K. The J_c values of the Sm-123 (x = 0) films measuring 7 × 10⁸ A/m² for 5 T at 77 K are comparable to that of NbTi for 5 T at 4.2 K. Furthermore, the superconducting properties in Sm-123 change with the substitution of Sm-Ba. By observing the c-axis oriented high-J_c Sm-123 thin films using the cross-section transmission electron microscopy, we detected the existence of finely dispersed a-axis oriented domains with a size of about 10 nm in the c-axis oriented matrix. Electron microscopic studies with EDX have revealed that the Sm/Ba ratio fluctuates within the range of x = 0 to 0.14 with a wavelength of ∼400 nm. It is considered that these domains are formed by a cation combining with the substituted Sm/Ba and a growth temperature difference on the a-axis oriented Sm-123 phase which has a c-axis orientation phase. High-J_c values in high magnetic fields at 77 K demonstrate the potential of REBCO films for high-field applications of oxide superconductor.