Superconductor World Record Tops 240K

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18 May 2009
Superconductors.ORG
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Superconductors.ORG herein reports efforts to increase the Tc of the
233K superconductive material, announced in March 2009, have been
successful. Producing a new world record near 242K, the host compound
has the formula (Tl4Ba)Ba4Ca2Cu10Oy and is believed to have a 9212/2212C
intergrowth structure (shown below left).

The chemical formula is written (Tl4Ba)Ba4 to indicate an extra
barium atom is being substituted into a thallium atomic site. The
purpose behind this 20% substitution is to hole-dope the insulating
layer. Heavy metal candidates with oxidation states lower than +3
included mercury, cadmium and barium. However, both mercury and cadmium
create a topological defect in the structure due to their affinity for
other atomic sites. This left barium as the best candidate for doping.

[to see the graphics and read the rest of this story, click the below
link]


http://www.superconductors.org/242K.htm