Deposition and reduction of infinite-layer Sr_1-xLa_xCuO₂ films

Electron-doped infinite-layer (IL) Sr_1-xLa_xCuO₂thin films were grown on bare and lattice-matched Ba_0.55Sr_0.45TiO₃-buffered LaAlO₃(100) substrates by magnetron sputtering, and their structures and electrical properties were investigated systematically for various deposition and reduction conditions. The a- and c-axis-oriented films were obtained on LaAlO₃and LaAlO₃//Ba_0.55Sr_0.45TiO₃substrates, respectively. For the caxis-oriented films, short-time (<6 min) reduction annealing in vacuum followed by deposition was effective for the removal of excess apical oxygen that was incorporated during deposition. The removal of excess apical oxygen was evidenced by the shortened c-axis and the appearance of superconductivity. However, subsequent annealing led to the elongation of the c-axis and loss of superconductivity. The a-axis-oriented films exhibited a similar behavior, although the time scale of such films for reduction annealing was significantly larger than that of the c-axis films. The implications of these results are discussed in terms of the oxygen sublattice in the IL compound.