On the enlargement of the lattice parameter c in sputter deposited in situ prepared thin films of YBa2Cu3Ox

The in situ growth of YBa2Cu3Ox (123) thin films by sputtering was studied at different partial pressures of oxygen, keeping the total sputtering pressure to a constant value of 40 Pa. The grown films were characterized to investigate the previously reported increase in the lattice parameter c and the variation of the superconducting transition temperature T-c with the parameter c which is found to be different from that of bulk samples. The increase in the parameter c is observed only when the films are prepared at low partial pressures of oxygen and is not dependent on the total sputtering pressure. Under these conditions, the growth promoted is non-equilibrium which facilitates the formation of an apical oxygen defect structure. For the maximum apical oxygen deficit, the c parameter is found to be 1.1815 nm. This structure has an onset superconducting transition temperature at 75 K. The apical oxygen deficiency decreases on increasing the oxygen partial pressure and this fact accounts for the observed linear variation of T-c with the lattice parameter c. The apical oxygen defect phase can be gainfully used to prepare superconductor-normal-superconductor (SNS) junctions based purely on 123 material.