This book encompasses the science, measurement, fabrica­ tion, and use of superconducting materials in large scale and small scale technologies. The present book is in some sense a continuation and completion of a series of two earlier books based on NA TO Advanced Study Institutes held over the last decade. The first book in the series entitled Superconducting Machines ~nd Devices: Large Systems Appli­ cations edited by S. Foner and B. B. Schwartz (1974) represented a compilation of all the applications of superconducting technology. The second book entitled Superconductor Applications: Squids and Machines, edited by B. B. Schwartz and S. Foner (1977) reviewed small scale applications and up-dated the large scale applications of superconductiv­ ity at that time. These two books are both introductions and advanced reference volumes for almost all aspects of the applications of super­ conductivity. The growth of applied superconductivity has mushroomed in the decade of the 1970's. Technologies which were discussed in the beginning of the 1970's are now beyond the prototype stage. Materials development and performance in operating systems is the basis of the continued applications and economic viability of super­ conducting technology. In this book, a complete review of all materials technology is presented by leading authorities who were instrumental in the development of superconducting materials technology. The present book is based on the NATO Advanced Study vi PREFACE Institute entitled Superconducting Materials: Science and Technology which was held from August 20 to August 30, 1980 in Sintra, Portugal.

1 Overview of Superconducting Materials Development.- I. Introduction.- II. Superconducting Materials of the First Kind.- A. Discovery.- B. Magnetic Properties.- C. Flux Penetration.- D. Nature of the Superconducting Transition.- 1. Bulk phase transition.- 2. Thin film phase transition.- E. The Two Fluid Model.- F. The Microscopic Theory.- III. Superconducting Alloys and Compounds, Early Work.- A. Introduction.- B. Critical Temperature Behavior.- C. Magnetic Field Behavior.- IV. Raising Tc With New Materials.- A. Introduction.- B. Transition Metal Alloys.- C. Carbides and Nitrides.- D. A15 Compounds.- 1. Progress in raising Tc.- 2. Present Tc situation.- 3. Factors depressing Tc.- 4. Other features of A15 behavior.- V. Superconductors of the Second Kind.- A. Introduction.- B. Another Kind of Superconductor.- C. Type II Materials.- VI. Unusual Materials and Future Possibilities.- A. Introduction.- B. Intercalation Compounds.- C. Organic Superconductors.- D. Low Carrier Density Superconductors.- E. Magnetic Superconductors.- F. Future Possibilities.- 2 Practical Superconducting Materials.- I. Introduction.- A. Practical Applications of Superconducting Materials.- B. Superconducting Materials in Common Use.- C. Problems in the Utilization of Superconducting Materials.- II. Stability: the General Problem.- A. Degradation and Training.- B. The Disturbance Spectrum.- C. Mechanical Sources of Disturbance.- D. Distributed Disturbances.- E. Point Disturbances.- F. Composite Conductors.- III. Flux Jumping.- A. General.- B. Screening Currents and the Critical State Model.- C. Adiabatic Theory of Flux Jumping.- D. Filamentary Composites.- E. Dynamic Stability.- F. Dynamic Stability with Finite Superconductor Thickness.- IV. C0ryogenic Stabilization.- A. Size Effects.- B. Principlesof Cryogenic Stabilization.- C. Boiling Heat Transfer.- D. Resistivity of the Normal Metal.- E. Heat Conduction Effects.- F. Effect of Finite Superconductor Size.- G. Forced Flow Cooling.- H. Superfluid Helium.- I. Cryogenic Stabilization in Practice.- V. AC Losses.- A. The Fundamental Loss Mechanism.- B. Hysteresis Loss.- C. Hysteresis Loss with Transport Current.- D. Filamentary Composites.- E. Self-Field Losses in Filamentary Composites.- F. Longitudinal Field Effects.- G. Combined Losses.- VI. Quenching and Protection.- A. The General Problem.- B. Temperature Rise.- C. Voltage.- D. Self-Protecting Magnets.- E. Other Protection Techniques.- VII. Measurement Techniques.- A. General.- B. Measurement of Critical Transport Current.- C. Measurement of Magnetization.- D. Measurement at Different Temperatures.- 3 Niobium-Titanium Superconducting Materials.- I. Introduction.- II. Metallurgical and Structural Properties.- A. Phases of the Niobium-Titanium System.- B. Cold-Worked Microstructures.- C. Elastic and Plastic Mechanical Behavior.- D. Metallurgical Properties of Related Systems.- III. Physical Properties.- IV. Superconducting Properties.- A. Basic Properties.- 1. Transition temperature and upper critical field.- 2. Paramagnetic limitation and spin-orbit scattering.- 3. Nb-Ti base ternary and quaternary systems.- B. The Superconducting Critical Current Density.- 1. Measurement techniques.- 2. Critical current densities.- V. Industrial and Fabrication Considerations.- VI. Future Developments and New Directions.- A. Conventional Composites.- B. Unconventional Developments.- 4 Metallurgy of Continuous Filamentary A15 Superconductors.- I. Introduction.- II. History of the "Bronze Process".- A. Early History.- B. Evolution of the Process.- 1. The Ta diffusionbarrier.- 2. The external diffusion process.- 3. The internal tin diffusion process.- 4. Bronze in Nb tubing.- 5. WRAP process.- 6. Other modifications.- III. Metallurgical Principles.- A. Thermodynamic Considerations.- B. Kinetics.- 1. Growth mechanisms.- 2. Experimental results.- IV. Influence of Metallurgical factors on Superconducting Properties.- A. Strains in Composite Superconductors and Their Influence on the Superconducting Properties.- B. Critical Temperatures.- 1. Effects of heat treatments.- 2. Effects of additives.- C. Critical-Current Densities and Magnetic Fields.- 1. Flux pinning (the scaling law).- 2. Temperature dependence.- 3. Grain size dependence.- 4. Effects of heat treatments and alloying.- 5. What is required for high Jc?.- V. Future Directions.- 5 Fabrication Technology of Superconducting Material.- I. Introduction.- II. Technology OF Solid Solution Superconductors.- A. Basic Properties of NbTi Alloys.- B. The influence of thermal treatment in the region of 873 K.- C. Mechanical Properties of NbTi Alloys.- D. Stress-Strain Behavior at Elevated Temperatures.- E. Raw Materials and Melting of NbTi.- F. Melting NbTi Alloys.- G. Sources of Inhomogeneities and Imperfections in the Molten Ingots.- H. Conductors and Fabrication Parameters.- I. Extrusion Technology.- 1. Extrusion billets and sealing techniques for single and multiextrusion.- 2. Extrusion presses and extrusion parameters.- 3. Extrusion temperature and preheating.- 4. Extrusion ram speed.- 5. Conductors containing mixed substrate.- J. Drawing Machinery, Twisting and Current Optimization.- K. Current Density Optimization and Properties of Monolithic Filamentary Conductors.- L. The Anisotropy of Rectangularly~Shaped Conductors.- M. Occurrence of the Ti Cu-Phase.- III. A15 Solid Solution Conductors.- A. Basic Properties of Nb3Sn and V Ga.- B. Principles of Solid State Diffusion.- C. Fabrication of the Conductors and Technology of High Sn-Content Bronzes.- D. Conductor Optimization with Respect to Layer Growth, Recrystalization, Kirkendall Effect,Filament Diameter and Filament Distribution.- E. Influence of Mechanical Strain on Electrical Properties.- F. Remarks About the Measurement of Critical Current Density of Technical Conductors.- G. Stabilization and Examples of Technical Conductors.- IV. Conductor Assembly By Braiding, Cabling, Mechanical Strengthening and Adding Stabilizers.- A. Technical Production of Flattened Cables and Braids.- B. Hollow Conductors and Fabrication Principles.- C. Fabrication of High Current, High Strength Hollow Conductors.- 1. Strands.- 2. Cr-Ni core with Kapton insulation.- 3. Cabling and Soldering.- 4. Strip for the conduit.- 5. Conductor completion.- V. Future Directions.- A. Solid Solution Superconductors.- B. A15 Superconductors.- 6 Alternative Fabrication Technologies for A15 Multifilamentary Superconductors.- I. Introduction.- II. Conventional Process Mechanical Assembly.- A. Historical Note.- B. Nb3Sn Technology.- C. Status.- D. Need for Alternate Technologies.- III. IN SITU Solidification.- A. Introduction.- B. The Natural Dispersion of the Superconductor.- 1. Phase diagram, solidification process.- 2. Melting and casting techniques.- C. Transformation into a Filamentary Superconductor.- 1. Mechanical deformation.- 2. Tin addition.- 3. Diffusion and reaction heat-treatment.- D. Superconducting Properties.- 1. Overall Jc of Cu-Nb.- 2. Overall Jc of Cu-Sn wires.- 3. Overall Jc of Cu-Nb-Sn versus Nb concentration.- 4. Overall Jc of Cu-V-Ga.- E. Mechanical Properties.- 1. Mechanical properties of Cu-Nb-Sn.- 2. Pre-stressmodel.- 3. Mechanical properties of Cu-V-Ga.- F. Experimental Observations on Connectivity.- 1. Random distribution.- 2. Filament geometry.- 3. Acid test.- 4. Unified perculation-proximity.- G. Research in Progress.- H. Scale-up Technologies.- IV. Powder Metallurgy.- A. Introduction.- B. Cold Process.- 1. Experimental technique.- 2. Materials selection.- 3. Results.- 4. Potential.- 5. Research in progress.- C. Hot Process.- 1. Experimental technique.- 2. Results.- 3. Potential.- D. Infiltration Process.- 1. Experimental technique.- 2. Results.- 3. Features.- 4. Scale-up technology.- V. Other Processes.- A. Metastable Solid Solution (Stoichiometric).- B. Controlled Precipitation.- C. Mechanical Alloying.- D. Modified Jelly Roll.- E. Energy Research Foundation (ECN) Process.- VI. Concluding Commentaries Future Developments.- 7 Mechanical Properties and StrainEffects in Superconductors.- I. Introduction.- A. Sources of Mechanical Loads in Magnets.- 1. During fabrication.- 2. Differential thermal contraction.- 3. The Lorentz force.- B. Mechanical Properties of Superconductors.- II. Stress-Strain Characteristics.- A. Micromechanical Model.- B. Stress-Strain Characteristics for Practical Conductors.- III. Effect of Uniaxial Strain on JC, Hc2, and Tc.- A. Mechanical-Electrical Interaction.- B. Jc-? Characteristics for Practical Superconductors.- 1. Multifilamentary NbTi.- 2. Multifilamentary Nb3Sn.- 3. Multifilamentary V3Ga.- 4. CVD Nb3Ge tape.- C. Strain Scaling Law - Prediction of JC (B,?).- 1. Scaling of pinning force curves.- 2. Strain scaling law.- 3. Application to practical multifilamenttary Nb3Sn conductors.- D. General Scaling Law - Prediction of J (T, B, ?).- E. Uniaxial-Strain Criterion for Magnet Design.- IV. Bending Strain.- A. Effect of Bending on Jc.- B.Prediction of Bending-Strain Degradation from Uniaxial-Strain Measurements.- 1. Long twist pitch.- 2. Short twist pitch.- 3. Application.- C. Bending Strain Limits for Magnet Design.- D. Methods for Minimizing Bending Degradation.- 1. Cabling.- 2. Wind-and-react magnet fabrication.- V. Fatigue.- A. Matrix Degradation.- 1. NbT.- 2. Nb3 Sn.- B. Micromechanical Model.- VI.Training.- A. Stress-Relief Model.- B. Materials.- C. Techniques for Minimizing Training.- 1. Crack arrestors.- 2. Bond breakage and friction.- 3. Programmed winding tension.- 4. Magnet shakedown without quenching.- VII. Summary and Future Research Needs.- A. Summary of Material Strain Limits for Magnet Design.- B. Future Research Areas.- 8 Phase Diagrams of Superconducting Materials.- I. Introduction.- II. Experimental Determination of High Temperature Phase Diagrams.- A. Sample Preparation.- 1. Arc melting.- 2. r.f. melting in water-cooled Crucibles.- 3. r.f. melting in graphite or ceramic crucibles.- 4. Levitation melting.- 5. Other melting techniques.- B. Homogenization Heat Treatments.- C. Direct Observation Methods.- 1. Differential thermal analysis (DTA).- 2. Thermal analysis on levitating samples (LTA).- 3. Electrical resistivity at high temperatures.- D. Indirect Observation Methods.- 1. Simultaneous stepwise heating.- 2. Splat cooling of liquid samples.- 3. Argon jet quenching on solid samples.- 4. Superconducting "memory".- III. Determination of Phase Diagrams Below 300 K.- A. Factors Influencing the Superconducting Data.- 1. Ordering effects.- 2. Shielding effects.- B. Low Temperature Specific Heat.- 1. Calorimetric detection of shielding effects.- 2. Shielding in multifilamentary Cu-Nb3Sn wires.- 3. Calorimetric observation of low temperature phase transitions.- C. Electrical ResistivityBelow 300 K.- IV. Criteria for Phase Stability and Superconductivity.- A. The Brewer Plots.- 1. Does Au behave like a transition element?.- 2. The relative stability of intermetallic phases.- 3. The A15 phase.- B. Criteria for Superconductivity.- V. Phase Fields and Superconductivity in Binary "Electron Compounds".- A. The hep Structure (A3 type).- B. The A2 Compounds.- C. "Atypical" A15 Compounds.- 1. The V-(Re, Os, Ir, Pt, Au) system.- 2. The electronic structure of electron compounds: the two-band model.- 3. The Nb-(Os, Ir, Pt, Au) system.- 4. The Cr-(Os, Re, Pt) system.- 5. The Mo-(Re, Os, Ir, Pt) system.- 6. The Ti-system.- 7. Characterization of "atypical" A15 compounds.- VI. Phase Fields and Superconductivity in Binary and Pseudobinary "TYPICAL" A15 COMPOUNDS.- A. The V~x3Au and Nb~3Au systems.- B. The Systems V3B (B = Ga, Si, Ge, "Al", and Sn).- 1. V3Ga.- 2. V3Si and the martensitic transformation.- 3. V3Ge.- 4. "V3AI".- 5. V3Sn.- C. V.-Based Pseudobinary Compounds.- 1. V3 (AU1-xPt3).- 2. V0.75(Ga1-xSix).- D. Nb3B (B = Ge, Ga, A1, Sn, and Sb).- 1. Nb-Ge.- 2. Nb-Ga.- 3. Nb-Al.- 4. Nb3Sn.- 5. Nb3Sb.- E. Nb-Based Pseudobinary Compounds.- 1. Nb3 CAu1-x Ptx).- 2. Nb3Cal1-x bx) (B = Ge, Si, Ga, Be, B, As,...).- F. Mo-Based Binaries and Ternaries.- 1. Mo3Ge and Mo3Si.- 2. Mo3(Ge1-xSix).- G. General Correlations for A15 Compounds.- 1. The superconducting transition temperature.- 2. Electronic specific heat.- 3. Type of formation of A15 compounds.- 4. Variation of the lattice parameter in Nb-based A15-type compounds.- VII. Phase Fields and Superconductivity Rhombohedral Mo Chalcogenides (Chevrel Phases)A. Binary Mo-S System.- A. Binary Mo-System.- B. CuxMo6S8 System.- C. PbxMo6S8 System.- D. Mo6Se8, CYuXMo6Se8, Pbx Mo6Se8.- E. GeneralCorrelationsfor Rhombohedral Compounds.- F. Comparison with the A15 Compounds.- 9 Josephson Junction Electronics: Materials Issues and Fabrication Techniques.- I. Introduction.- II. Device Principles and Materials Requirements.- A. Josephson Junctions: Tunnel Junctions and Weak-Link Devices.- 1. Tunnel junctions.- 2. Weak-link microbridge Josephson junctions.- B. Other Circuit Elements.- C. Summary of Superconducting Device and Material Parameters of Importance.- III. Integrated Circuit Fabrication.- A. Junctions with Pb-alloy Electrodes.- 1. Integrated circuit fabrication.- 2. Pb-alloy electrode materials.- 3. Tunnel barrier.- B. Junctions with Niobium Electrodes.- C. Comparing Junctions with Nb and Pb-Alloy Electrodes.- IV. Stability of Films and Devices During Cycling Between 350 K And 4.2 K.- A. Origin of the Cycling Problem.- B. Strain Relaxation Mechanisms.- C. Film and Device Stability.- D. Choosing a Material for Mechanical Stability.- V. Electron Tunneling and Tunnel Barrier Formation.- A. Theory of Tunneling: Ideal Cases of Interest.- B. Complications that can Occur in Practical Tunnel Junctions.- C. Tunnel Barrier Formation.- 1. Crown-oxide barriers.- 2. Deposited barriers.- VI. Advanced Materials and Devices.- A. Materials of Interest.- B. Thin-Film Deposition Techniques and Film Properties.- C. Advanced Tunneling Devices.- 1. Small Tunnel junctions.- 2. Intermetallic compounds.- 3. Transition metal alloys.- D. Artificial (Deposited) Barriers.- E. Weak-Link Microbridges.- 10 Chevrel Phase High Field Superconductors.- I. Introduction.- II. Chemistry and Structure.- A. Preparation.- B. Chemistry.- C. Structure.- III. Physical Properties.- A. Superconducting Temperatures.- 1. Lattice properties, phonons.- 2. Electronic properties, charge transfer.- B. Upper Critical Fields.- C. Magnetism, Coexistence of Magnetism and Superconductivity.- D. Critical Currents and Applications.- IV. New Materials Proceeding from the Linear Condensation of the Octahedral Mo6 and Clusters.- A. In~3Mo15Se19 Containing Mo6 and Mo9 clusters.- B. M2Mo15Se(M = K, Ba, In, Tl) and (M2Mo15S19 (M = K Rb, Cs) containing Mo6 and Mo9 clusters.- C. M2Mo9S11(M = K, Tl).- D. M2Mo6X6 M2 Mo6S6 (M = K, Rb, Cs), M2Mo6 Se6 (M = In, Tl, Na, K), M2Mo6Te6 (M = In, Tl, Na, K) with one-aimensional clusters (Mo6/2)?.- V. Conclusion.- 11 Superconducting Proximity Effect for in Situ and Model Layered Systems.- I. Model Systems.- II. Boundary Conditions At the Superconducting- Normal Interface.- A. Electron Tunneling.- B. Thermal Conductivity.- III. Phonon Spectral Function, ?2F(?).- IV. Supercurrents Through Normal Barriers.- A. Thickness Dependence.- B. Temperature Dependence.- C. Magnetic Field Dependence.- V. Flux Entry Fields.- VI. Implications for in Situ Composites.- 12 Amorphous Superconductors.- I. Introduction.- A. Preparation Techniques.- B. Structural Properties.- C. The Anderson Theorem.- II. Systematics of TC.- A. Non-transition Metals.- B. Transition Metals.- III. Electron-Phonon Interaction.- A. The Ratio of Energy Gap to Transition Temperature (2?(0)/KB TC).- B. a2F(?) and ?.- C. Origins o£ Strong Electron-Photon Inter action.- 1. Amorphous non-TM superconductors.- 2. AIS superconductors.- IV. Critical Fields.- A. The Upper and Lower Critical Fields.- B. The Temperature Coefficient of Critical Fields.- V. Potential Applications.- A. High Field Magnets.- B. Josephson Junctions.- 13 Reviews of Large Superconducting Machines.- I. Introduction.- II. Technical Superconductors.- III. Superconducting Magnets for High Energy Physics.- IV. Levitated Trains-Electrodynamic Levitation System.- V. Superconducting Coils for Magnetic Separation.- VI. Rotating Machinery with Superconducting Windings.- A. Generators.- B. DC Machines.- VII. Superconducting High Power Cables.- VIII. Superconducting Switches.- IX. Magnet Systems for Fusion Reactors.- X. Superconducting Magnets For MHD Plants.- XI. Superconducting Magnet Energy Storage (SME Storage).- 14 Superconductivity in Canada.- 15 Research Activities in Superconductivity in China.- I. Introduction.- II. Background.- III. Superconducting Materials.- A. NbTi.- B. Nb3Sn.- C. V3Ga.- D. New Materials.- IV. Superconducting Magnet Systems.- A. Laboratory Magnets.- B. High Energy Physics.- C. Controlled Thermonuclear Reaction Technology.- D. Superconducting Machines.- E. Magnetic.- F. Other Applications.- V. Josephson Junction Devices.- A. Voltage Standard.- B. Magnetometer.- C. High Frequency Devices.- 16 European Efforts on Superconducting Materials.- 17 Review of National Efforts in Middle Europe.- I. Introduction.- II. Austria and Switzerland.- A. Members in Switzerland.- B. Expenditures Within COST-action 56 in Switzerland.- 1. First phase of the COST-action 56 (1977-1979).- 2. Second phase of the COST-action 56 (1980-1982).- C. Projects in Switzerland.- D. Members in Austria.- E. Funding Level in Austria.- F. Projects in Austria.- III. Czechoslovakia.- IV. GDR (German Democratic Republic).- V. Hungary.- VI. Poland.- 18 Recent Developments in High-Field Superconductors in Japan.- I. Introduction.- II. The Development of V3Ga.- A. Surface Diffusion Process.- B. Composite Diffusion Process.- III. Improvements in High-Field Current-Carrying Capacities of Composite-Processed A15 Superconductors.- IV. Superconducting and Mechanical Properties of the in Situ Processed V3Ga.- V. Developments in the V2Hf-Base C-15 Type Superconductors.- VI. Developments of Multifilamentary A15 Conductors in Japanese Research Groups other than Nrim.- 19 Programs on Superconducting Materials and Miniature Cryocoolers in the United States.- I. Summary.- II. Introduction.- III. Superconducting Materials.- A. Bulk Materials.- 1. Liquid Solute Diffusion (LSD).- 2. Chemical Vapor Deposition (CVD).- 3. Electron Beam Deposition (EBD).- 4. Solid State Diffusion (SSD).- B. Thin Films.- IV. Small Cryocoolers.- V. Trends.- A. Bulk Superconducting Materials.- B. Thin-Film Superconducting Materials.- C. Small Cryocoolers.- 20 Large-Scale Applications of Superconductivity in the United States: An Overview.- I. Introduction.- II. Low Field Regime (H < 2T).- A. General Remarks.- B. Power Transmission Lines.- 1. General Remarks.- 2. Superconducting AC power transmission lines (SPTL).- 3. Superconducting DC power transmission lines.- C. RF Cavities for Particle Accelerators.- III. Intermediate Field Regime (2 < H < 5T).- A. General Remarks.- B. Magnets for High Energy Physics (HEP).- C. Rotating Electrical Machines.- 1. DC acyclic (homopolar) motors.- 2. AC machines (generators).- D. Energy Storage Magnets.- IV. High Field Regime (H >2T).- A. General Remarks.- B. Magnetohydrodynamics (MHD).- C. Magnetically Confined Fusion.- V. Superconducting Materials.- VI. Helium Conservation.- VII. Miscellaneous Applications.- A. Electromagnetic Launchers.- B. Magnetic Separation.- 21 Reports on Some Superconducting Materials Companies in The United States.- I. Airco, Inc., Carteret, New Jersey 07008.- A. Introduction.- B. Materials Fabrication.- II. Intermagnetics General Corporation, Waterbury, Connecticut and Guilderland, New York.- A. Introduction.- B. Manufactured Materials.- 1. Ductile alloy superconductors.- 2. A15 superconductors.- 3. External bronze process.- C. Conclusions.- III. Supercon, Inc.- A. Introduction.- B. High Field Superconductors.- IV. Teledyne WAH Chang Co., Albany, Oregon 97321.- A. Introduction.- B. Material Supply and Manufacturing.