University of California Berkeley MSE 200A Fall 2017 Characteristics of

University of california berkeley mse 200a fall 2017

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University of California, Berkeley MSE 200A Fall, 2017 Characteristics of Superconductivity Zero resistance Material loses all resistance at a critical temperature, T c Meissner Effect Material expels magnetic fields below a critical field, H c Only certain materials exhibit this behavior
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J.W. Morris, Jr. University of California, Berkeley MSE 200A Fall, 2017 Cooper Pairs Electrons polarize the lattice in their immediate vicinity. They may attract one another through the intermediary of polarizing phonons
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J.W. Morris, Jr. University of California, Berkeley MSE 200A Fall, 2017 The Superconducting Elements H Li Na K Rb Cs Fr Be Mg Ca Sr Ba Ra Sc Y La Ti Zr Hf V Nb Ta Mo W Mn Tc Re Ru Os Rh Ir Pd Pt Cu Ag Au Zn Cd Hg B Al Ga In Tl C Si Ge Sn Pb N P As Sb Bi O S Se Te Po F Cl Br I At He Ne Ar Kr Xe Ra 6.0 0.11 5.38 0.39 0.55 0.12 9.5 4.48 0.92 0.01 7.77 1.4 0.51 100 47 <10 1420 1980 830 95 1 1410 198 70 0.65 65 0.14 19 0.88 53 0.56 30 4.15 412 1.14 105 1.09 51 3.40 293 2.39 171 3.72 309 7.19 803 Ce Pr Nd U Pm Np Sm Pu Eu Tb Ho Er Tm Yb element transition temperature (K) critical field (gauss = 10 T) -4 = superconductor = superconducting under special conditions = ferromagnetic
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J.W. Morris, Jr. University of California, Berkeley MSE 200A Fall, 2017 Domain of Superconductivity Superconductivity when T < T c H < H c j < j c Superconductors may be – Elements – Compounds Two basic types Differ in their response to H J J c T T c H H c
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J.W. Morris, Jr. University of California, Berkeley MSE 200A Fall, 2017 Types of Superconductors Type I superconductor Magnetic field penetrates at H c Both H c and j c small; little industrial interest Type II superconductor H penetrates gradually over a range from H c1 to H c2 >>H c1 With proper microstructure, can have high j c -M H H c -M H H c1 H c H c2
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J.W. Morris, Jr. University of California, Berkeley MSE 200A Fall, 2017 Conductivity in Type II Conductors In type II conductor, H penetrates in flux vortices Quantized lines of magnetic flux Density increases as H increases to H c2 Current imposes Lorenz force on flux lines Vortices will be swept out (j c small) unless microstructural pinning Proper microstructural pinning can produce very high j c Nb 3 Sn 11 9 7 0 10 20 B(tesla) log(j c )[A/in 2 ]
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J.W. Morris, Jr. University of California, Berkeley MSE 200A Fall, 2017 Properties of Type II Conductors compound T c (K) H c2 (Tesla at 4K) NbTi 12 12 NbN 17.3 47 Nb 3 Sn 18.5 24 Nb 3 Ge 23.2 38 PbMo 6 S 8 15.3 60 YBa 2 Cu 3 O 7 92 >100 Bi 2 Sr 2 CaCu 2 O 8 85 >100 j c controlled by microstructure • Attainable j c increases with H c2 j c decreases with T ( flux creep ) High- T c conductors have low j c
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J.W. Morris, Jr. University of California, Berkeley MSE 200A Fall, 2017 Microstructure: Nb 3 Sn Bronze process multifilamentary conductor Thousands of filaments in cross-section Fine-grained filaments pin flux Create high j c (H)
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J.W. Morris, Jr.
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  • Fall '08
  • Staff
  • Magnetism, Magnetic Field, University of California, J.W. Morris

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