Study of structural developments in the bismuth-strontium-calcium-copper-oxide superconductors from amorphous precursors obtained by quenching from melts
Abstract
Investigations were made of structural developments in the Bi-Sr-Ca-Cu-O superconductors from their amorphous precursors obtained by quenching from melts. A disturbing feature of the Bi-Sr-Ca-Cu-O superconductors is that materials prepared by the sintering process include several superconducting phases, making it very difficult to separate the 110 K high-T$\sb{\rm c}$ phase. In addition, the density of such materials is usually quite low. This study demonstrates that quenching melts of the Bi-Sr-Ca-Cu oxides produces amorphous materials of extremely high density from which favorable superconductors of nearly 100% theoretical density can be prepared under proper annealing conditions. With this melt-quenching method, high-quality materials of a single 85 K or 110 K superconducting phase have been obtained through a nucleation and growth process by annealing their dense amorphous precursors under appropriate conditions. The data reveals that materials with only a single 110 K superconducting phase consist of a mixture of the two layer and the three layer structure, strongly suggesting that the two layer structure can also constitute the 110 K high-T$\sb{\rm c}$ phase. In connection with the above work, Bi-Sr-Ca-Cu-O superconducting films prepared by an in-situ melting technique were studied. Oriented (Bi, Pb)-Sr-Ca-Cu-O superconducting films with T$\sb{\rm c,0}$ as high as 95 K have been obtained. This technique offers compositional uniformity and the ability to form large areas of smooth films, and seems useful if thick films of $\sim$20 $\mu$m in thickness are required for practical applications. The importance of prereaction of powders and the effect of substrates on superconducting properties of films are also discussed.
Degree
Ph.D.
Advisors
Sato, Purdue University.
Subject Area
Materials science|Condensation|Electrical engineering
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