Physical Properties of High–Temperature Superconductors

The discovery by J.G. Bednorz and K.A. Müller in 1986 that the superconducting state can exist in complex oxides above 30 K revitalized the field of superconductivity. This opened up the area of high–temperature (high–Tc) superconductivity, and a whole range of technological applications, in magnet technology, and the power sector.

Physical Properties of High–Temperature Superconductors provides an overview of the known cuprate– and iron–based high–Tc superconductors and their physical properties. The most important families of cuprate high–Tc superconductors, rules for their critical temperatures and their crystal structures, are described. In addition, the special case of the intermediate–temperature superconductor magnesium diboride (MgB2) is considered. Further aspects presented are the synthesis of these materials, the manufacture of superconducting wires and tapes, and the deposition of superconducting films. Finally, there is an outlook on future research and development.

The book illustrates the status of research and development in high–Tc superconductivity, and is suitable for graduate students and researchers.

About the Author xi

Series Preface xiii

Preface xv

Acknowledgment xvii

List of Tables xix

Nomenclature xxiii

1. Brief History of Superconductivity 1

1.1 Introduction 1

1.2 Milestones in the Field of Superconductivity 1

1.2.1 Early Discoveries 1

1.2.2 Progress in the Understanding of Superconductivity 4

1.2.3 Discovery of High–Temperature Superconductivity 4

1.2.4 Importance of Higher Transition Temperatures for Applications 6

References 7

2. The Superconducting State 13

2.1 Introduction 13

2.2 Electrical Resistance 13

2.3 Characteristic Properties of Superconductors 22

2.4 Superconductor Electrodynamics 30

2.5 Thermodynamics of Superconductors 34

References 42

3. Superconductivity: A Macroscopic Quantum Phenomenon 45

3.1 Introduction 45

3.2 BCS Theory of Superconductivity 45

3.3 Tunneling Effects 52

References 66

4. Type II Superconductors 69

4.1 Introduction 69

4.2 The Ginzburg Landau Theory 70

4.3 Magnetic Behavior of Type I and Type II Superconductors 73

4.4 Critical Current Densities of Type I and Type II Superconductors 81

4.5 Anisotropic Superconductors 83

References 84

5. Cuprate Superconductors: An Overview 87

5.1 Introduction 87

5.2 Families of Superconductive Cuprates 88

5.3 Variation of Charge Carrier Density (Doping) 93

5.4 Summary 96

References 97

6. Crystal Structures of Cuprate Superconductors 101

6.1 Introduction 101

6.2 Diffraction Methods 102

6.2.1 Bragg Condition 102

6.2.2 Miller Indices 102

6.2.3 Classification of Crystal Structures 103

6.2.4 X–ray Diffraction 104

6.2.5 Neutron Diffraction 106

6.3 Crystal Structures of the Cuprate High–Temperature Superconductors 107

6.3.1 The Crystal Structure of La2CuO4 107

6.3.2 The Crystal Structure of YBa2Cu3O7 108

6.3.3 The Crystal Structures of Bi–22(n 1)n High–Temperature Superconductors 111

6.3.4 The Crystal Structures of Tl–based High–Temperature Superconductors 113

6.3.5 The Crystal Structures of Hg–based High–Temperature Superconductors 121

6.3.6 Lattice Parameters of Cuprate Superconductors 124

References 127

7. Empirical Rules for the Critical Temperature 131

7.1 Introduction 131

7.2 Relations between Charge Carrier Density and Critical Temperature 132

7.3 Effect of the Number of CuO2 Planes in the Copper Oxide Blocks 135

7.4 Effect of Pressure on the Critical Temperature 138

7.5 Summary 146

References 146

8. Generic Phase Diagram of Cuprate Superconductors 151

8.1 Introduction 151

8.2 Generic Phase Diagram of Hole–Doped Cuprate Superconductors 151

8.2.1 Generic Phase Diagram: An Overview 151

8.2.2 Symmetry of the Superconducting Order Parameter 153

8.2.3 The Pseudogap 158

8.3 Summary 161

References 162

9. Superconducting Properties of Cuprate High–Tc Superconductors 165

9.1 Introduction 165

9.2 Characteristic Length Scales 166

9.3 Superconducting Energy Gap 169

9.4 Magnetic Phase Diagram and Irreversibility Line 171

9.5 Critical Current Densities in Cuprate Superconductors 174

9.5.1 Definitions of the Critical Current 174

9.5.2 Critical Currents in Polycrystalline Cuprate Superconductors 178

9.5.3 Critical Currents in Bulk Cuprate Superconductors 182

9.5.4 Critical Currents in Superconducting Films 183

9.6 Grain–Boundary Weak Links 188

9.7 Summary 193

References 194

10. Flux Pinning in Cuprate High–Tc Superconductors 203

10.1 Introduction 203

10.2 Vortex Lattice 204

10.3 Consequences of Anisotropy and Intrinsic Pinning 205

10.4 Thermally Activated Flux Creep 207

10.5 Irreversibility Lines 216

10.6 Summary 224

References 226

11. Transport Properties 231

11.1 Introduction 231

11.2 Normal–State Resistivity 232

11.3 Thermal Conductivity 249

11.4 Summary 256

References 257

12. Thermoelectric and Thermomagnetic Effects 265

12.1 Introduction 265

12.2 Thermoelectric Power of Cuprate Superconductors 269

12.3 Nernst Effect 273

12.4 Summary 276

References 276

13. Specific Heat 279

13.1 Introduction 279

13.2 Specific Heat at Low Temperatures 280

13.3 Specific Heat Jump at the Transition to Superconductivity 284

13.4 Specific Heat Data up to Room Temperature 287

13.5 Summary 289

References 289

14. Powder Synthesis and Bulk Cuprate Superconductors 293

14.1 Introduction 293

14.2 Synthesis of Cuprate Superconductor Powders 294

14.2.1 Yttrium–based Superconductors 294

14.2.2 Bismuth–based Superconductors 296

14.2.3 Thallium–based Superconductors 303

14.2.4 Mercury–based Superconductors 311

14.3 Bulk Cuprate High–Tc Superconductors 317

14.3.1 Introduction 317

14.3.2 Bi–2212 and (Bi,Pb)–2223 Bulk Superconductors 317

14.3.3 RE–123 Bulk Superconductors 320

14.4 Summary 326

References 327

15. First– and Second–Generation High–Temperature Superconductor Wires 339

15.1 Introduction 339

15.2 First–Generation High–Tc Superconductor Wires and Tapes 340

15.2.1 Introduction 340

15.2.2 Ag/Bi–2212 Wires and Tapes 341

15.2.3 Ag/Bi–2223 Tapes 351

15.3 Second–Generation of High–Tc Superconductor Tapes 361

15.3.1 Introduction 361

15.3.2 Manufacturing Routes for Coated Conductors 362

15.3.3 Critical Current Densities of Coated Conductors 370

15.3.4 Lengthy Coated Conductors 379

References 381

16. Cuprate Superconductor Films 393

16.1 Introduction 393

16.2 Film Deposition Techniques 394

16.2.1 Preparation of Bismuth–based Cuprate Superconductor Films 394

16.2.2 Preparation of Thallium–based Cuprate Superconductor Films 394

16.2.3 Preparation of Mercury–based Cuprate Superconductor Films 397

16.2.4 Preparation of RE–123 Superconductor Films 404

16.3 Multilayers of Ultrathin Films 407

16.4 Strain Effects 412

16.5 Summary 416

References 417

17. MgB2 An Intermediate–Temperature Superconductor 423

17.1 Introduction 423

17.2 Physical Properties of MgB2 424

17.3 MgB2 Wires and Tapes 437

17.4 MgB2 Bulk Material 444

17.5 MgB2 Films 446

17.6 Summary 450

References 450

18. Iron–Based Superconductors A New Class of High–Temperature Superconductors 459

18.1 Introduction 459

18.2 Critical Temperatures of Iron–based Superconductors 461

18.3 Crystal Structures of Iron–based Superconductors 467

18.4 Physical Properties of Iron–based Superconductors 471

18.5 Synthesis of Iron–based Superconductors 477

18.6 Critical Current Densities in Iron–based Superconductors 477

18.7 Summary 482

References 482

19. Outlook 489

19.1 Introduction 489

19.2 The Investigation of Physical Properties 490

19.3 Conductor Development 491

19.4 Magnet and Power Applications 492

References 493

Author Index 497

Subject Index 501

Rainer Wesche Ecole Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas (CRPP), Switzerland