Fabrication of Nd_1-xCa_xBa₂Cu ₃O_7-δ (x = 0-0.3) single crystalline films by tri-phase epitaxy

In order to fabricate single crystalline films with controlled carrier concentration, we have applied the tri-phase epitaxy (TPE) for Ca doped NdBa₂Cu₃O_7-δ (NCBCO). The TPE is a process to deposit a solid thin film from a thin liquid layer, while film precursors are being fed from the gas phase into the liquid layer to maintain the quasi-equilibrium between the growing solid layer and the overlying liquid layer. The NCBCO films were prepared by the TPE using pulsed laser deposition (PLD) under the conditions designed from the thermodynamic phase diagram. The NCBCO TPE film obtained, exhibited a higher crystallinity and a larger grain size as compared with the film by the conventional PLD without using the liquid flux layer. The TPE films had atomically flat surfaces with 1.2nm height steps, which corresponded to the lattice constant along the c-axis of the crystal structure. In the NCBCO TPE films, Ca was homogeneously distributed over the film thickness. By the post-annealing for incorporation of oxygen in the film, we could obtain crack free superconducting NCBCO films.