Preface ........................................................ XI
1 Fundamentals ................................................. 1
1.1 Introduction to Superconductivity in High-Temperature
Superconductors (HTSCs) .................................. 1
1.1.1 Introductory Remarks ............................... 1
1.1.2 Internal Nomenclature .............................. 3
1.1.3 Critical Currents and Flux Motion in
Superconductors .................................... 3
1.1.4 Magnetization Curve of a Type II Superconductor .... 7
1.1.5 Determination of Critical Currents from
Magnetization Loops ................................ 9
1.1.6 Magnetic Relaxation ............................... 11
1.1.7 Electric Field-Current Relation ................... 13
1.1.8 Peculiarities of HTSCs in Comparison to
Low-Temperature Superconductors ................... 15
1.1.9 Basic Relations for the Pinning Force and Models
for its Calculation ............................... 16
1.2 Features of Bulk HTSCs .................................. 18
1.2.1 Bulk HTSCs of Large Dimensions .................... 19
1.2.2 Potential of Bulk HTSC for Applications ........... 20
1.3 Solid-State Chemistry and Crystal Structures of HTSCs .... 22
1.3.1 Crystal Structures and Functionality .............. 22
1.3.2 Chemistry and Doping .............................. 24
1.3.3 Intrinsic Doping: Variations of Stoichiometry ..... 25
1.3.4 Defect Chemistry .................................. 26
1.3.5 Extrinsic Doping .................................. 27
2 Growth and Melt Processing of YBa2Cu3O7 ....................... 31
2.1 Physico-Chemistry of RE-Ba-Cu-O Systems ................. 31
2.1.1 Phase Diagrams and Fundamental Thermodynamics ..... 31
2.1.2 Subsolidus Phase Relationships .................... 33
2.1.3 The Influence of Oxygen on Phase Equilibria:
the System Y-Ba-Cu-O .............................. 35
2.1.4 The Oxygen Nonstoichiometry in 123 phases:
YBa2Cu3O7-δ (YBa2Cu3O6+x) ........................... 37
2.1.5 Phase Relationships in Y-Ba-Cu-O in the Solidus
and Liquidus Range ................................ 39
2.1.6 Phase Relationships and the Liquidus Surface in
Systems Ln-Ba-Cu-O (Ln=Nd, Sm,..) ................. 42
2.1.7 Additional Factors ................................ 45
2.2 Preparation of Polycrystalline RE123 Materials .......... 45
2.2.1 Synthesis of HTSC Compounds ....................... 45
2.3 Growth of YBa2Cu3O7 Single Crystals ...................... 46
2.4 Processing of "Melt-Textured" YBaCuO Bulk Materials ..... 47
2.4.1 Experimental Procedure ............................ 47
2.4.2 Mass Flow, Growth Rates, Kinetic and
Constitutional Undercooling ....................... 50
2.4.3 Developing Microstructures: Morphology,
Inclusions, Defects ............................... 53
2.5 Modified Melt Crystallization Processes For YBCO ........ 60
2.5.1 Variants of the YBa2Cu3O7-Y2BaCuO5 Melt-Texturing
Process ........................................... 60
2.5.2 Processing Mixtures of Y123 and Yttria ............ 60
2.5.3 Processing in Reduced Oxygen Partial Pressure ..... 63
3 Pinning-Relevant Defects in Bulk YBCO ....................... 67
4 Properties of Bulk YBCO ..................................... 75
4.1 Vortex Matter Phase Diagram of Bulk YBCO ................ 75
4.1.1 Irreversibility Fields ............................ 75
4.1.2 Upper Critical Fields ............................. 78
4.1.3 Vortex Matter Phase Diagram ....................... 79
4.2 Critical Currents and Pinning Force ..................... 82
4.2.1 Transport Measurements ............................ 82
4.2.2 Magnetization Measurements ........................ 83
4.3 Flux Creep .............................................. 86
4.3.1 Flux Creep in Bulk YBCO ........................... 86
4.3.2 Reduction of Flux Creep ........................... 87
4.3.3 Pinning Properties from Relaxation Data ........... 89
4.4 Mechanical Properties ................................... 91
4.4.1 Basic Relations ................................... 91
4.4.2 Mechanical Data for Bulk YBCO ..................... 93
4.5 Selected Thermodynamic and Thermal Properties ........... 96
4.5.1 Symmetry of the Order Parameter ................... 96
4.5.2 Specific Heat ..................................... 98
4.5.3 Thermal Expansion ................................. 99
4.5.4 Thermal Conductivity ............................. 101
5 Trapped Fields ............................................. 105
5.1 Low-Temperature Superconductors ........................ 105
5.2 Bulk HTSC at 77 К ...................................... 105
5.3 Trapped Field Data at 77 К ............................. 109
5.4 Limitation of Trapped Fields in Bulk YBCO at Lower
Temperatures ........................................... 110
5.4.1 Magnetic Tensile Stress and Cracking ............. 111
5.4.2 Thermomagnetic Instabilities ..................... 113
5.5 Magnetizing Superconducting Permanent Magnets by
Pulsed Fields .......................................... 115
5.6 Numerical Calculations of the Local Critical Current
Density from Field Profiles ............................ 119
5.6.1 Inverse Field Problem: Two-Dimensional
Estimation ....................................... 120
5.6.2 Three-Dimensional Estimation ..................... 122
5.7 Visualization of Inhomogeneities in Bulk
Superconductors ........................................ 125
6 Improved YBa2Cu3O7-δ-Based Bulk Superconductors and
Functional Elements ........................................ 129
6.1 Improved Pinning Properties ............................ 129
6.1.1 Chemical Modifications in YBa2Cu3O7 ............... 129
6.1.2 Sub-Micro Particles Included in Bulk YBCO ........ 135
6.1.3 Irradiation Techniques ........................... 136
6.2 Improved Mechanical Properties in YBa2Cu3O7-δ
Composite Materials .................................... 138
6.2.1 Fundamentals of the Processing and Growth of
YBCO/Ag Composite Materials ....................... 138
6.2.2 Processing and Results ........................... 140
6.2.3 Properties of Bulk YBaCuO/Ag Composite
Materials ......................................... 141
6.3 Near Net Shape Processing: Large Sized Bulk
Superconductors and Functional Elements ................ 142
6.3.1 Finishing and Shaping ............................ 143
6.3.2 The Multi-Seed Technique ......................... 144
6.3.3 Rings of 123 Bulk Materials ...................... 144
6.3.4 Joining of Separate Single Grains ................ 146
6.4 Bulk Materials and Processing Designed for Special
Applications ........................................... 148
6.4.1 Infiltration Technique and Foams ................. 148
6.4.2 Long-Length Conductors and ControUed-Resistance
Materials ........................................ 149
6.4.3 Bi2212 Bulk Materials and Rings .................. 152
6.4.4 Batch Processing of 123 Bulk Materials ........... 151
7 Alternative Systems ........................................ 155
7.1 Impact of Solid Solutions Ln1+уВа2-уCu3O7±δ on Phase
Stability and Developing Microstructure ................ 155
7.2 Advanced Processing of Ln123 ........................... 160
7.2.1 Oxygen Potential Control ......................... 160
7.2.2 Oxygen-Controlled Melt Growth Process (OCMG) ..... 161
7.2.3 Isothermal Growth Process at Variable Oxygen
Partial Pressure (OCIG) .......................... 161
7.2.4 Composition Control in Oxidizing Atmosphere for
Growing (CCOG) ................................... 163
7.3 Alternative Seeding Techniques ......................... 165
7.4 Further LnBa2Cu3O7-Based Materials ...................... 165
7.5 Ag/LnBaCuO Composites with Large Lanthanide Ions ....... 166
7.5.1 Fundamentals of Processing ....................... 166
7.5.2 Reactions Near the Seed-Melt Interface ........... 167
7.5.3 Growth and Properties of Ag/LnBaCuO Composites ... 168
8 Peak Effect ................................................ 171
8.1 Peak Effect (due to Cluster of Oxygen Vacancies) in
Single Crystals ........................................ 172
8.2 Peak Effect in Bulk HTSC ............................... 175
9 Very High Trapped Fields in YBCO Permanent Magnets ......... 179
9.1 Bulk YBCO in Steel Tubes ............................... 179
9.1.1 Magnetic Tensile Stress (in Reinforced YBCO
Disks) ........................................... 179
9.1.2 Trapped Field Measurements ....................... 181
9.2 Resin-Impregnated YBCO ................................. 184
9.3 Trapped Field Data of Steel-reinforced YBCO ............ 185
9.4 Comparison of Trapped Field Data ....................... 188
10 Engineering Aspects: Field Distribution in Bulk HTSC ....... 191
10.1 Field Distribution in the Meissner Phase .............. 192
10.1.1 Field Cooling .................................. 192
10.1.2 Zero-Field Cooling ............................. 193
10.2 Field Distribution in the Mixed State ................. 194
10.2.1 Field Cooling .................................. 194
10.2.2 Zero-Field Cooling ............................. 195
11 Inherently Stable Superconducting Magnetic Bearings ........ 199
11.1 Principles of Superconducting Bearings ................ 199
11.1.1 Introduction to Magnetic Levitation ............ 199
11.1.2 Attributes of Superconducting Magnetic
Bearings with Bulk HTSC ........................ 200
11.2 Forces in Superconducting Bearings .................... 201
11.2.1 Forces in the Meissner and the Mixed State ..... 201
11.2.2 Maximum Levitational Pressure in
Superconducting Bearings ....................... 204
11.3 Force Activation Modes and Magnet Systems in
Superconducting Bearings .............................. 207
11.3.1 Cooling Modes .................................. 207
11.3.2 Operational Field Cooling with an Offset ....... 209
11.3.3 Maximum Field Cooling Mode ..................... 211
11.3.4 Magnet Systems for Field Excitation in
Superconducting Bearings ....................... 211
11.3.5 Force Characteristics .......................... 236
11.4 Optimized Flux Concentration Systems for
Operational-Field Cooling (OFCo) ...................... 220
11.4.1 Stray Field Compensation ....................... 221
11.4.2 Dimensional Optimization of System
Components ..................................... 221
11.5 Parameters Influencing the Forces of Superconducting
Bearings .............................................. 225
11.5.1 Critical Current Density ....................... 225
11.5.2 Temperature .................................... 226
11.5.3 Flux Creep ..................................... 227
11.5.4 HTSC Bulk Elements Composed of Multiple
Isolated Grains ................................ 229
11.5.5 Number of Poles of the Excitation System ....... 232
11.6 Applications of Superconducting Bearings .............. 233
11.6.1 Bearings for Stationary Levitation ............. 234
11.6.2 Bearings for Rotary Motion ..................... 236
11.6.3 Bearings for Linear Motion ..................... 241
11.7 Specific Operation Conditions ......................... 245
11.7.1 Precise Positioning of Horizontal Rotating
Axis ........................................... 245
11.7.2 Bulk HTSCs Cooled Below 77 К ................... 246
11.7.3 Cooling the Excitation System along with
the Superconductor ............................. 247
11.7.4 Dynamics of Rotating Superconducting
Bearings ....................................... 247
11.8 Numerical Methods ..................................... 249
11.8.1 Perfectly Trapped Flux Model (2D) .............. 250
11.8.2 Perfectly Trapped Flux Model (3D) .............. 252
11.8.3 Vector-Controlled Model (2D) ................... 253
12 Applications of Bulk HTSCs in Electromagnetic Energy
Converters ................................................. 259
12.1 Design Principles ..................................... 259
12.2 Basic Demonstrator for Application in Electrical
Machines - Hysteresis or Induction Machines ........... 261
12.3 Trapped-Field Machine Designs ......................... 263
12.4 Stator-Excited Machine Designs with Superconducting
Shields -The Reluctance Motor with Bulk HTSC .......... 269
12.5 Machines with Bulk HTSCs - Status and Perspectives .... 273
13 Applications in Magnet Technologies and Power Supplies ..... 279
13.1 Superconducting Permanent Magnets with Extremely
High Magnetic Fields .................................. 279
13.1.1 Laboratory Magnets ............................. 279
13.1.2 Magnetic Separators ............................ 280
13.1.3 Sputtering Device .............................. 283
13.1.4 Superconducting Wigglers and Undulators ........ 284
13.2 High-Temperature Superconducting Current Leads ........ 284
13.3 Superconducting Fault Current Limiters ................ 285
13.3.1 Inductive Fault Current Limiters ............... 286
13.3.2 Resistive Superconducting Fault Current
Limiters ....................................... 287
13.3.3 Status of High AC Power SFCL Concepts .......... 288
13.4 High-Temperature Superconducting Magnetic Shields ..... 290
List of Abbreviations ...................................... 293
Index ...................................................... 295
|
