Surprising Zinc Superconductor Lends Support
to +2,+1 Theory


18 July 2016
Superconductors.ORG

        Zinc suppresses superconductivity in high temperature superconductors. This is a well-known fact among materials scientists. It does so by altering the structure of the unit cell, disrupting the mechanism of superconductivity. So if a simple structure could be found that was superconductive while containing zinc, this would provide additional support for the theory that +2,+1 metals are a key component of HT superconductivity. This is because zinc is a +2,+1 metal.

        Superconductors.ORG herein reports that a new family of zinc-based, ternary superconductors has been discovered. This system blends zinc, magnesium, and oxygen to achieve transition temperatures (Tc) in the range of the copper-oxides. The magnetization plots at page top show Meissner transitions near 115 Kelvin for ZnMgO2 and near 132K for Zn2MgO3. Below: Zn3MgO4 transitions close to 152K. [1] The volume fraction of all three new materials is low. Lines have been drawn through the noise to approximate the average of the data points.



      Though the atomic structures of ZnO and MgO (shown at left) are completely different, when they are blended together oxygen gets sandwiched between disparate-weight metals, both of which have +2,+1 oxidation states. This is the critical arrangement that appears to facilitate high-temperature superconductivity.



      

       A number of +2,+1 metals have already been found to be facilitators of HTSC. These include Cu, Mg, Sr, Ca and Cd. As such, the discovery of Zn superconductivity buttresses the working theory that states: When +2,+1 metals of different atomic weights are positioned on opposite sides of an oxygen atom, periodic compression from lattice vibrations forces a momentary valency shift in the metal from +2 to +1, causing holes to appear at the oxygen site. That positive oxygen ion then acts as a mediator, encouraging electrons to pair up, producing a superconductive state. See the below animation.



         



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

ZnO   99.9%   (LW Ind. & Sci.)
MgO   99.95%   (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. This transition near 152K appeared as a minority phase in the plots of both ZnMgO2 and Zn2MgO3.

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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