有機酸塩熱分解法により作製したBi系酸化物焼結超伝導体の特性と組織

Abstract

The Bi-base high-TC oxide superconductors have been synthesized by thermal decomposition of organic acid salt. This process does not require strict pH control unlike other chemical preparation process, facilitating an easy preparation of oxide superconductors. Furthermore, this process allows an uniform and quantitative addition of other elements. The precursor powders less than 10 μm in diameter have been obtained by this process. The powders prepared by the present process exhibit TC’s over 100 K in a shorter sintering time than those prepared by the conventional powder process.The effects of intermediate process, e.g. pressing and grinding between heat-treatment cycles, on superconducting properties and grain morphologies were investigated. The TC’s are appreciably increased by an intermediate pressing, and reduced by intermediate grinding. The TC of 109 K has been obtained by intermediate pressed specimens, with total heat-treatment time of 60 h. The maximum JC (77 K) so far obtained in the sintered specimen is 1540 A/cm2.The X-ray diffraction analyses performed on these specimens reveal that the intermediate pressing enhances the diffraction peaks of high-TC phase, with strong (00l) orientation, and suppresses those of low-TC phase. Meanwhile, the diffraction peaks of high-TC phase are reduced by the intermediate grinding. The changes in TC and JC by the intermediate pressing and grinding have been discussed relating to the structure changes. The Bi-base oxide powders prepared by the present process may be useful for the conductor fabrication.