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High Tc Superconductors

High Tc Superconductors. Kevin W. Cooper Sajida Khan Yuan Zhang. Superconductors – A Brief Introduction. Properties DC electrical resistivity goes to zero at a low temperature. (Called Tc: critical temperature)

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High Tc Superconductors

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  1. High Tc Superconductors Kevin W. Cooper Sajida Khan Yuan Zhang

  2. Superconductors – A Brief Introduction • Properties • DC electrical resistivity goes to zero at a low temperature. (Called Tc: critical temperature) • A superconductor in a weak magnetic field will work like a perfect diamagnet. • Meissner effect: magnetic flux present in superconductor is ejected when superconductor cooled through Tc. • Superconductivity destroyed by strong enough magnetic field, Hc.

  3. Types of Superconductors • Type I Superconductors (soft superconductors) • many types of pure materials have this behavior • Zn, Cd, Hg, etc. • Hc is too low for applications in superconducting magnets • Type II Superconductors • tend to be alloys • has a region that is a mixture of superconducting and non-superconducting states (vortex state) • Hard superconductors (large magnetic hysteresis) MRI’s

  4. Applications for Superconductors MagLev Trains Source: www.superconductors.org MRI (non-invasive health imaging) Possible applications could be in power generation and transmission.

  5. TBCO • Tl2Ca2Ba2Cu3O10 • Ceramic cuprate superconductor • Tc=125 K (Beyers, R.) or 120K (Kittel) • (2223) • Three Cu perovskite-like units separated by Tl-O bi-layers. • Tc seems to go up with number of CuO2 layers.

  6. TBCO nominal unit cell Source: R. Beyers, et. al. Crystallography and microstructure of Tl-Ca-Ba-Cu-O superconducting oxides

  7. Tl-O layer Ba layer CuO2 layer Ca layer CuO2 layer Ca layer CuO2 layer Ba layer Tl-O layer Tl-O layer

  8. Body centered (b.c.) tetragonal cell Lattice Parameters: a = 3.822(4) angstroms c = 36.26(3) angstroms Note: c ~ 10 a c a a Source: R. Beyers, et. al. Crystallography and microstructure of Tl-Ca-Ba-Cu-O superconducting oxides

  9. Naming Scheme # of CuO2 planes within a conducting block. 2223 # of layers separating CuO2 planes. # of spacing layers between CuO2 blocks. # of insulating layers between conducting blocks. (Tl-O layers) Source: www.superconductors.org

  10. Perovskite Source: http://cst-www.nrl.navy.mil/lattice/struk.picts/e2_1.s.png

  11. Perovskite like structure In TBCO this structure is deformed to the tetragonal structure of the CuO2 units. Ba or Ca Oxygen Copper Source: J. Phillips. “Physics of High-Tc Superconductors”

  12. Bonding The conduction occurs along the CuO2 planes. The bond type between Cu and O is covalent. The average Cu oxidation state being +2 for ideal Tl-O bilayer systems. Source: R. Beyers, et. al., and R. Vasquez, et. al.

  13. Bonding – ctd. • Ba and Ca are in the same group, thus having similar properties. • Both would tend to act as electron donors, forming an ionic bond with the O (as indicated in R. Vasquez, et. al.)

  14. References R. Beyers, et. al. “Crystallography and microstructure of Tl-Ca-Ba-Cu-O superconducting oxides” Appl. Phys. Lett. 53 (5), 1 August 1988. C. Kittel. “Introduction to Solid State Physics” 8th ed. John Wiley & Sons, Inc. (2005). J. C. Phillips. “Physics of High-Tc Superconductors”. Academic Press, Inc. (1989). S. Subramanyam, and E. Raja Gopal. “High Temperature Superconductors”. John Wiley & Sons. (1989). R. P. Vasquez, et. al. “Chemical bonding in Tl cuprates studied by x-ray photoemission” Physical Review B 60 (6), 1 August 1999. www.superconductors.org www.nrl.navy.mil/lattice/struk.picts/e2_1.s.png

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