Transport Properties Of Tapes Research Articles

Effect of the phase assemblage of the precursor powder on the phase transformation and microstructure of Ag/Bi-2223 tapes

The effect of the phase assemblage of the precursor powder on the properties of Ag/Bi-2223 tapes was investigated. The phase assemblage of the precursor powder was controlled by changing the calcination temperatures from 800 to or by adding 2223 seed particles to the precursor powder. The phase transformation kinetics, microstructure and transport properties of tapes were strongly dependent on the phase composition of precursor powder. The tapes fabricated from the powder calcined at lower temperatures (800 and ), which contained no 2223 phase and a relatively large amount of secondary phase, resulted in a microstructure with a larger grain size and a higher transport critical current. These tapes also appeared to have an appreciable incubation period in an isothermal annealing experiment with various soaking times. The phase transformation kinetics and microstructural development was pertinent to the nucleation and growth process for the mechanism of 2223 formation.

The effects of stoichiometry in the (Tl,Pb)/sub 1/(Sr,Ba)/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ system on the transport properties of Ag-clad tapes

Evidence shows that texturing is necessary to achieve high current densities and strong links in the Tl-based superconductors. Conventional sintering is not sufficient to achieve strong links, but instead, melt processing is required to produce platelets which can develop into a textured structure. Changes in the stoichiometry of the precursor powders can lead to enhanced melt-phase formation at lower processing temperatures. An experimental matrix was designed with variations in the Tl/Pb ratio, the total Tl/Pb content, and the Ca/Cu level to change liquid formation and subsequent grain growth. Thirteen compositions were prepared in both pellet form and as Ag-clad tapes to investigate grain development over a range of thermal processing conditions. Tapes were produced using unreacted powders by the powder-in-tube method and processed by conventional furnace annealing. We report here on the transport properties of these tapes, their strong link behavior, and microstructural development.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>