Superconductors.ORG reports signs of superconductivity near 267K magnetic (-6C, 21F). This suggests a resistive Tc (temperature critical) around 264-265 Kelvin, which would be another world record for a 9223 copper-oxide structure
After the recent discovery (also by Joe Eck) of superconductivity near 258 Kelvin, an effort was made to identify a small anomaly a few degrees above 260K in the magnetization plots of (Tl4Ba)-9223-Mg2. A stoichiometric mix with one less Mg and one more Cu atom was produced using the “layer cake” method. The resulting formulation (Tl4Ba)Ba2MgCu8O13+ produced diamagnetic transitions near 267K in five separate magnetization tests
Moving Mg into the dominant C1 axis increases the planar weight ratio from 5.0 to 6.3. And since greater planar weight disparity (PWD) translates into higher Tc, we should see an increase in Tc. The resulting location of (Tl4Ba)-9223-Mg in the plot below agrees favorably with the tendency of the curves to roll over and flatten as we approach room temperature.
As with prior discoveries that are asymmetrical along the C axis, the volume fraction of the 265K material is low (less than 1%). Even so, it is believed this is the one investors will watch. Once a refinement method is developed to purify this material, superconductors will move rapidly from an industrial novelty into our everyday lives. As a result of a low VF, numerous R-T and magnetization tests may be necessary to see the respective transitions above the noise. This discovery is being released into the public domain without patent protection in order to encourage additional research. Synthesis was by the solid state reaction method.
The copper-oxides are strongly hygroscopic. All tests should be performed immediately after annealing.