Studies of the improvement in microstructure of Y2O3 buffer layers and itseffect on YBa2Cu3O7-x film growth

Two kinds of Y2O3 buffer layers have been directly deposited on cube-textur ed Ni substrates by electron beam evaporation under different gas pressures . One is deposited at 10(-5) Torr air (a single-layer buffer). In order to reveal the improvement of the microstructure, the other is formed at first under 5 x 10(-4) Torr and then 10(-6) Ton of N-2 (a double-layer buffer). A s a result, the double-buffer layer obtained is more than 97% {100} orienta tion and is a relatively denser structure. YBa2Cu3O7-x overlayers are depos ited by pulsed-laser deposition on these buffer layers. Large YBa2Cu3O7-x p op-off areas are seen far the single-buffer samples. These areas are elimin ated on the double-layer buffer. However, the critical current does not inc rease appreciably for the YBa2Cu3O7-x film on the double-layer buffer, even though the microstructure of the buffer is improved. Other defects probabl y yielded percolative current flow and a low critical current density in th e YBa2Cu3O7-x layers.