Reformulating BSCCO and TBCCO for Higher Tc

4 April 2016
Superconductors.ORG

        Superconductors.ORG herein reports that, after nearly 3 decades, the critical transition temperatures (Tc) of BSCCO and TBCCO have finally been increased through reformulation and substitution. Classic Bi-2212 has a Tc near 110 Kelvin and Tl-2212 transitions near 118K.[1,2] With this reformulation Tc is improved by almost 30 degrees in both superconductors.

       The key to improving these copper-oxides was to increase the electron density of the anion layers. Legacy BSCCO and TBCCO both have +2 calcium in the anion. By substituting +4 tellurium into a 3212 structure or +3 yttrium into the original 2212 structure, the availability of free electrons in the anion rises to a level complementary to the cation layers. The result outperforms even the mercuric cuprates.

       The magnetization plots at page top show a Meissner transition for Bi-3212-Te around 139K in the upper left. Then, in the upper right, Tl-3212-Te transitions near 147K. Both are multiphasic due to tellurium going into other atomic sites. Even so, the 147 K material establishes a new record for being the highest Tc superconductor that will form with a high volume fraction through the stoichiometric mixing of chemicals.

       Meanwhile, the below plots result from yttrium being substituted into the calcium site of Tl-2212. The below left plot shows a sharp diamagnetic transition of around 30 milligauss near 139K. And the below right plot shows about a 2% resistance drop - also near 139K. The straight lines drawn through the noise represent the average of the data points, skewing apart at Tc. Though the Tc of this thallium 2212 cuprate is lower than the thallium 3212 cuprate, the volume fraction is slightly higher.


           


       Neither of the 3212 discoveries is likely to see commercialization due to low VF. However, Tl-2212-Y might. These discoveries confirm that overdoped copper-oxide superconductors can produce a high transition temperature, if the anion layers are doped to match the cation layers.

       Stoichiometric amounts of the below chemicals were used in the synthesis of these compounds:

Y2O3   99.99%   (Alfa Aesar)
Tl2O3   99.99%   (Alfa Aesar)
BaCuO   99.9%   (Alfa Aesar)
CuO   99.995%   (Alfa Aesar)
TeO2   99.99%   (Alfa Aesar)
Bi2O3   99.99%   (Alfa Aesar)
SrO   97%   (Alfa Aesar)

       The chemical precursors were pelletized at 60,000 PSI. Those with tellurium-oxide were pre-sintered for 1 hour at 715C. If it contained bismuth-oxide, the pellet was then sintered for 3 days at 805C with no annealing. If the compound contained thallium-oxide, it was sintered at 860C for 36 hours and annealed for 10+ hours at 500C in flowing O2. Testing temperatures were determined using an Omega type "T" thermocouple and precision OP77 DC amplifier. The magnetometer employed twin Honeywell SS94A1F Hall-effect sensors with a tandem sensitivity of 50 mv/Gauss.


1. H. Maeda, Y. Tanaka, M. Fukutumi, and T. Asano (1988). "A New High-Tc Oxide Superconductor without a Rare Earth Element". Jpn. J. Appl. Phys. 27 (2): L209–L210. Bibcode:1988JaJAP..27L.209M. doi:10.1143/JJAP.27.L209.
2. Sheng, Z. Z.; Hermann, A. M. (1988). "Bulk superconductivity at 120 K in the Tl–Ca/Ba–Cu–O system". Nature 332 (6160): 138–139. Bibcode:1988Natur.332..138S. doi:10.1038/332138a0.

RESEARCH NOTE: The copper-oxides are strongly hygroscopic. All tests should be performed immediately after annealing.

RE-PUBLICATION NOTICE: Elsevier Publishing, dba Elsevier Science, as well as Morris Communications, both print and broadcast divisions, are specifically prohibited from re-publishing any part of this news story.


E. Joe Eck
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