Hisao Hattori

Growth of the 2223 Phase in Leaded Bi-Sr-Ca-Cu Oxide under Reduced Oxygen Partial Pressure

The growth process of 2223 phase in a leaded Bi-Sr-Ca-Cu oxide system has been investigated under various oxygen partial pressures using differential thermal analysis, combined with XRD of the quenched specimen. It is shown that under a slow heating rate, the DTA curves exhibit two or three endothermic peaks between 820 to 900°C, and the peak positions are lowered with reduction in the O2 partial pressure. The 2223 phase is found to grow most efficiently in the partial melting state sandwiched between the two endothermic peaks, and the temperature range between the two peaks becomes maximum around 0.1-atm O2 partial pressure.

Effects of Oxygen-Potential-Controlled Annealing on the Superconducting Properties of (Bi, Pb)2Sr2Ca2Cu3Oy Thin Films

The oxygen potential of thin films consisting of monophasic (Bi, Pb)2Sr2Ca2Cu3Oy was controlled by annealing them under various oxygen partial pressures. The Tc of (Bi, Pb)2Sr2Ca2Cu3Oy was found to decrease monotonously with decreasing oxygen potential. However, Tc did not change when annealed under higher oxygen pressure up to 2.9×104 torr. The carrier concentration was found to change with oxygen partial pressure, implying that oxygen supplies the carrier. An optimum range of the carrier concentration exists for attaining the highest Tc. This finding is consistent with those of other high Tc hole-type superconductors.

100) Oriented BSCCO Thin Film by RF Magnetron Sputtering

As-grown superconducting Bi-Sr-Ca-Cu-O thin film with fair (100) orientation was obtained on a MgO (100) substrate. Tc (R=0) of the film was 69K, and the transition width was 5K. Preferred orientation of the film was able to be controlled by the substrate temperature during deposition. Preferred orientation changed from (001) to (100) with decrease in the substrate temperature. This tendency is consistent with the one observed in the YBa2Cu3O7 thin film.

Fabrication and Characterization of BSCCO Films

A present stage of BSCCO film fabrication techniques is reviewed and metallographic structures of high and low Jc 2223 films are compared. Some difficulties associated with the 2223 film fabrication in an atmosphere of low oxygen partial pressure will be pointed out: 1)oxygen deficiency and 2) slow ordering of chemically similar elements, Sr and Ca. A new vacancy model of defected CuO2 planes is proposed for the hole source in the BSCCO system and based on this model an explanation is offered for the transformation of the semiconducting 2223 films into superconductors when annealed in an oxidizing atmosphere.