Superconductors.ORG herein reports the discovery of two new "infinite layer", non-toxic superconductors. The chemical formulas of the two compounds are YSrCa2Cu4Ox (Tc~101K) and BaSr2CaCu4Ox (Tc~90K). With the recent push by the electronics industry to implement RoHS (Restriction of Hazaradous Substances) in electronic products, these discoveries will add to the pool of non-toxic alternatives available to superconductor manufacturers.
YSrCa2Cu4Ox, with its higher Tc of 101K, has the best prospects of challenging YBCO - currently the most widely used non-toxic, high-temperature superconductor (Tc ~92K). This is because it contains calcium. Numerous researchers1 have found that calcium doping can increase the current-carrying capabilites across grain boundaries by as much as 35 percent. While Ca doping of YBCO lowers its Tc, calcium is native to this new material. So a higher Tc and Jc are intrinsic.
The other discovery BaSr2CaCu4Ox is less likely to have commercial success because of its multi-phasic content. (see plot above right)
While the intended structure is the 02"∞-1"∞ (infinite layer type shown above), some researchers assert that superconductivity actually springs from a tetragonal Srn+1CunO2n+1+d structure within the multiphasic mix2. Others insist the infinite layer structure is indeed correct, but that superconductivity exists only where the structure is alkaline-earth deficient3. Either way, a sharp resistive transition is clearly visible in the plots of both new discoveries (page top).
A crude magnetization test (shown above) was performed on the 101K material using twin Hall-effect sensors. Surprisingly, a second Meissner transition appears near 112K. This phase may be the known superconductor (Sr,Ca)CuO2, with Tc~110K.
The closest formula analog to the 101K material is the well-known 1-2-3 superconductor YSr2Cu3O7. However, its structure is 1212C with Tc ~62K.
A patent has been applied for the general formula Y(n)Sr(2-n)Ca2Cu4O8+, where "n" can be adjusted up or down from a value of 1, based on desired characteristics.
Synthesis of the materials was by the solid state reaction method. Stoichiometric amounts of the below precursors were mixed, pelletized and sintered for 11 hours at 890C. The pellets were then annealed for 10 hours at 500C in flowing O2.Y2O3 99.99% (Alfa Aesar)
- E. Joe Eck
Copywrite 2007 Superconductors.ORG
Patent Pending. Application #US60/966,885
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(1) J. Mannhart, et al
(2) H. Shaked, et al, ANL, and P.D. Han, et all, Univ. of Illinois, (1994)
(3) M. Azuma, et al, MIE University, Japan, Nature 356, 775 - 776 (April 1992)
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