超高真空系における酸化物高温超伝導体の酸素制御

抄録

The oxidation ability of various oxidants for Bi₂Sr₂CaCuO_x and related cuprates were evaluated both by experiments and by a thermodynamical calculation. When Bi₂Sr₂CaCu₂O_x sputtered films were treated at 400°C with such oxidants as photo-activated O₂, NO₂, O₃, and N₂O, significant Tc change was observed. This Tc change was found in parallel with the variation of c-lattice parameter and verified to originate from oxygen nonstoichiometry in the films by the Hall coefficient measurement. The highly oxidative property of NO₂, ozone, and atomic oxygen derived from this experiment was supported by the thermodynamical calculation for the oxidation of Cu₂O to CuO. The results were further utilized to grow alkaline earth cuprate films by pulsed laser deposition in ultrahigh vacuum (laser MBE). In situ RHEED and XPS analyses clearly indicated that alkaline earth cuprates could be grown epitaxially and laterally under such conditions as 700°C and 1×10^-7 NO₂pressure.