Kazuhiko Shinohara

Preparation of Y-Ba-Cu-O Superconducting Thin Film by Chemical Vapor Deposition

Y-Ba-Cu-O film was prepared by chemical vapor deposition using tris(2,2,6,6-tetramethyl-3,5-heptanedionato)yttrium(III) (Y(DPM)3), bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)barium(II) (Ba(HFA)2) and bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)copper(II) (Cu(HFA)2). Superconducting transition was observed with Tc(onset)=83 K and Tc(R=0)=65 K for these CVD films after an annealing process. Typical films of Y-Ba-Cu-O on a (001) SrTiO3 substrate exhibited the presence of YBa2Cu3Oy according to X-ray diffraction patterns.

Electrical Properties of YBa2Cu3Oy at High Temperatures

Electrical resistance of YBa2Cu3Oy (YBC) was measured from room temperature to 1123 K while varying oxygen partial presure. Electrical conduction mechanism in YBC changed from metallic to semiconductive around 700 K in air. Oxygen deficiency associated with temperature and oxygen partial pressure of the ambience dominated the electrical conduction mechanism.

Compositional Effects on In Situ YBaCuO Films Grown at Low Oxygen Pressures

YBaCuO films were grown by reactive coevaporation at various oxygen pressures and compositions. The Tcs of these films were strongly affected by composition, especially by the Ba/Y ratio. The composition ratios of Ba/Y optimized for Tc>85 K were found to decrease with decreasing oxygen pressure during growth.

Electrical Properties of Bi2Sr2Ca1-xYxCu2Oy at High Temperatures

Temperature dependence of the resistivity of Bi2Sr2Ca1-xYxCu2Oy compounds was measured in air and N2. The temperature dependence of the resistivity in this system showed behavior similar to that in Eu1+xBa2-xCu3Oy except for Bi2Sr2Y1Cu2Oy. The results of Bi2Sr2Y1Cu2Oy indicate that the hole is stable in the region where Cu1+ and Cu2+ exist. The high stability of holes suggests the possibility that the role of copper and oxygen in the electrical conduction of high-Tc oxide superconductors is separate.

Electrical Properties of Eu1+xBa2-xCu3Oy at High Temperatures

Oxygen partial pressure, PO2 , and temperature dependences of the resistances, R, of Eu1+xBa2-xCu3Oy compounds were measured to obtain knowledge about the effect of substitution of the trivalent Eu ions for the divalent Ba ions. The resistances of the samples depended on PO2 according to R∝PO2 -1/n. The exponents were caused to vary due to the substitution, which affected the relation between oxygen pressure and oxygen solubility in Eu1+xBa2-xCu3Oy compounds.