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Superconductors.ORG herein reports finding a new room-temperature superconductor with an exceptionally strong resistance change at Tc. To date 49 different compounds have been found that showed signs of room-temperature superconductivity (RTSC). But they all displayed weak resistive and magnetic transitions at Tc, pointing to a low volume fraction (VF). The typical resistance delta in those 49 RTSC materials was between 0.1% and 1.0%. However, this new discovery Tm8CaBa6Cu15Ox shows a resistance change greater than 8.0% of the bulk. This is evidenced by the plots at page top showing a drop from 14.5 ohms to 13.3 ohms as it enters a superconductive state. Then the warming test jumps from 13.1 ohms to 14.5 ohms coming out of a superconductive state. Tc appears to be around 41.6 Celsius (107 F).
The below magnetization test was performed to confirm RTSC is indeed at work, producing a 17 milligauss diamagnetic transition within one degree of 41.6C. And, at 17 milligauss, this represents about 8% of what a legacy superconductor like YBCO would produce in this magnetometer. Lines have been drawn through the quiescent noise to illustrate this Meissner transition.
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The inspiration for this discovery was an improved ReBCO formulation that was announced in February of this year. That material had an extraordinarily high volume fraction using the same chemical elements: Thulium, Calcium, and Barium in a Copper-Oxide matrix1. Since there seemed to be synergy at work, these same materials were reformulated to increase the planar weight ratio along the C2 axis from 11-to-1 to over 50-to-1. This required changing the structure type as well.
The previous 49 RTSC formulations also used very high planar weight ratios to achieve their room-temperature Tc's. But the strategy changed with this material. Instead of placing the heaviest metals in the cation layers, this arrangement has the period 6 elements distributed throughout both the cation and anion layers. It should be noted that, although the VF is indeed higher in this material, magnetic levitation of the pellet was not possible.
Stoichiometric amounts of the below chemicals were used in the synthesis of this compound:
BaCO3 99.95% 4.71 gr. (Alfa Aesar) (decomposes to BaO during calcination)
Tm2O3 99.99% 6.14 gr. (Stanford Materials)
CaCO3 99.95% 0.40 gr. (Alfa Aesar) (decomposes to CaO during calcination)
CuO 99.995% 4.75 gr. (Alfa Aesar)
The chemical precursors were mixed thoroughly in acetone, dried and pelletized. Then the pellet was calcined at 770C+ for 1 hour and sintered for 8 hours at 890C. Lastly, it was annealed for 10+ hours at 500C in flowing O2. Testing temperatures were determined using an Omega type "T" thermocouple. The magnetometer employed dual Honeywell SS94A1F Hall-effect sensors with a tandem sensitivity of 50 mv/Gauss operating within an ambient magnetic field of 550-600 milliGauss
RESEARCH NOTE: The copper-oxides are strongly hygroscopic. All tests should be performed immediately after annealing.
1. Lutetium should also work in the Thulium atomic site.E. Joe Eck
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