HTS Theory Gets A Boost from Rare Earth Metals


11 August 2016
Superconductors.ORG

        Superconductors.ORG herein announces that more support has been found for the periodic compression theory of high-temperature superconductivity. That theory asserts that metals of disparate weights, but with identical oxidation states, will produce superconductivity when they are positioned on opposite sides of an oxygen atom. Periodic compression from lattice vibrations causes the metals' valency to shift downward momentarily, creating a hole at the oxygen site. The positively-charged oxygen ion then facilitates the pairing of electrons, producing superconductivity.[1] To-date six different (+2,+1) metals have buttressed this theory by producing superconductivity in ternary compounds. Those metals are Cu, Mg, Sr, Ca, Cd, and Zn.

        Now it's been discovered that disparate-weight rare earth metals, when positioned on opposite sides of oxygen, can also produce superconductivity, even though they have (+3,+2) oxidation states. Like the divalent metals, rare earths normally bond at the higher of two oxidation states. So periodic compression can only lower their valency by one. However, unlike their divalent progenitors, the structure that forms is neither cubic nor tetragonal. Thus, it could be concluded that a collinear alignment of the metals with oxygen is not a requirement for superconductivity (see structures below left).




      The magnetization plots at page top show Meissner transitions of about 8 milligauss for TmYO3 and 4-5 milligauss for Tm2YO4.5. The below plot of Tm3YO6, which appeared as a minority phase in the other two formulations, shifts about 3-4 milligauss. The transition temperatures (Tc) were 117K, 130K and 140K respectively. Though the volume fraction is low, the evidence for superconductivity was unambiguous, appearing in over a half-dozen tests of each material.[2] Lines have been drawn through the noise to approximate the average of the data points.[3]




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

Tm2O3   99.99%   (Stanford Materials)
Y2O3   99.99%   (Alfa Aesar)

       The chemical precursors were pelletized at 60,000 PSI and sintered for 10 hours at 880C. They were then annealed for 10+ hours at 500C in flowing O2. Temperature was 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]  Prior research by ORNL and the University of Rome has determined that high-temperature superconductivity "arises from the oxygen ions". See: "High-Tc Superconductivity at the Interface between the CaCuO2 and SrTiO3 Insulating Oxides" Phys. Rev. Lett. 115, 147001 Published 28 September 2015. dx.doi.org/10.1103/PhysRevLett.115.147001

[2]  Since these were the strongest, repeating transitions, they are assumed to be the majority (stoichiometric) phase of each material. Weaker transitions at other temperatures, representing minority phases, were also observed.

[3]  The Tm2YO4.5 and Tm3YO6 plots show a "double dip" near Tc. This is because +3 and +2 thulium ions are typically magnetic. When combined with yttrium, reentrant behavior is seen.

RESEARCH NOTES: These oxides can be 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
2016 Superconductors.ORG
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