Processing and Fabrication of High Temperature Oxide Superconductors
Annual rept. 1 Aug 1988-30 Jun 1989
SRI INTERNATIONAL MENLO PARK CA
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During the past year, we have been optimizing a process for synthesizing super-conductor powders by freeze-drying. our objectives are to develop an understanding of the processing of these powders and to fabricate simple shapes from freeze-dried powders. We have synthesized a series of powders from solutions of barium acetate, copper nitrate, and yttrium nitrate, with pH values of 2.8 to 9.8 and calcined at temperatures from 510 to 908C. We are determining the surface area of these powders by BET AND XRD. Selected powders are being characterized by SEM, DTA, ICP analysis performed at Stanford University, carbon analysis, and tap density. The highest surface area in lightly milled powders of 4.4 sq mg was achieved with a pH of 4 in a series of experiments in which the Ba and Y solutions were mixed together before the Cu nitrate solution was added, then calcined at 825C. Surface areas decrease with increasing calcining temperature, however. It appears that calcining at 750 or 850 C gives the best critical temperature, with complete transitions at greater than 90K. Critical temperature measurements performed at Standford show that we have achieved our goal of a critical temperature of Tc 90K and a temperature difference, W, between 10 and 90 of transition of 2K.
- Physical Chemistry
- Solid State Physics