Superconductors.ORG reports high Tc has been advanced to 77 Celsius (170F, 350K) with the discovery of the compound Tl7Sn2Ba2MnCu10O20+. This exceedingly high transition temperature (Tc) was achieved by substituting manganese into the titanium atomic sites of the 65 Celsius superconductor announced in January 2014. This substitution increases the dielectric constant (K) of the anion in the “light” region of the H212 structure by two orders of magnitude.
Two examples of the Meissner transitions which consistently appeared near 77C in more than a dozen magnetization tests2. This is the 17th material found to display superconductivity above room temperature.
The graph below shows how Tc increases in the H212 structure as the dielectric constant (K) increases exponentially. As dioxides, silicon has a K of only 4, while titanium is near 100 and manganese has a colossal K near 10,000. The rise in Tc occurs despite the planar-weight-ratio (PWR) declining with progressively heavier elements (see right side of graph). Normally Tc goes down as PWR goes down.
This discovery provides more support for the theory that superconductivity in the layered cuprates originates in the oxygen layers where PWR is greatest. This is because the dielectric constants of the other metal-oxygen layers are not affected by substituting manganese into the titanium atomic sites.
The significance of this discovery also lies in helping to identify the most efficient combination of elements that can achieve superconductivity at room temperature. Since 77C is more than 50 degrees above room temperature, the unit cell size could be reduced as much as 25-35% and still be superconductive at room temperature. A smaller unit cell size would greatly simplify mass production.
This compound was synthesized using the layer cake method, as shown below. The pellet had over 100 interference layers. And, even using this layering technique, the volume fraction is low, requiring very sensitive test equipment.
Previous 65 celsius work
Superconductors.ORG reported a previous world superconductivity record has been increased to near 65 Celsius (338K, 149F) by reformulating the 53C superconductor announced in November 2013. In the reformulation silicon is replaced with titanium changing the chemical formula to Tl7Sn2Ba2TiCu10O20+.
Due to such an extraordinarily high transition temperature (Tc), two separate pellets were synthesized a week apart and both tested extensively. The plots at page top show two examples of the Meissner transition which appeared consistently near 65C in both pellets.1 The transitions are approximately 12 to 14 milli-Gauss in amplitude.
Some work with Joe Eck of superconductors.org and Oak Ridge National Lab
In December of 2011 Superconductors.ORG announced the discovery of the first true room-temperature superconductor – a senary oxycuprate with transition temperature near 28.5 Celsius. Shortly after that Dr. Thom Mason, Director of Oak Ridge National Laboratory, viewed the data graphs of this discovery online and called them “tantalizing hints” of room-temperature superconductivity. Now O.R.N.L. SQUID tests have confirmed a diamagnetic transition is occuring at 28.5C.
Samples of the compound (Tl5Pb2)Ba2Mg2Cu9O17+ were delivered to Oak Ridge Labs on December 18, 2013, and tests were performed using a commercial SQUID magnetometer.