Crystal Chemistry of High-Tc Superconducting Copper Oxides

The recent discovery of high-temperature superconductivity in copper­ based oxides is an event of major importance not only with respect to the physical phenomenon itself but also because it definitely shows that solid state chemistry, and especially the crystal chemistry of oxides, has a crucial place in the synthesis and understanding of new materials for future appli­ cations. The numerous papers published in the field of high Tc supercon­ ductors in the last five years demonstrate that the great complexity of these materials necessitates a close collaboration between physicists and solid state chemists. This book is based to a large extent on our experience of the crystal chemistry of copper oxides, which we have been studying in the laboratory for more than twelve years, but it also summarizes the main results which have been obtained for these compounds in the last five years relating to their spectacular superconducting properties. We have focused on the struc­ ture, chemical bonding and nonstoichiometry of these materials, bearing in mind that redox reactions are the key to the optimization of their supercon­ ducting properties, owing to the importance of the mixed valence of copper and its Jahn-Teller effect. We have also drawn on studies of extended defects by high-resolution electron microscopy and on their creation by ir­ radiation effects.

Contenu

1. Introduction: Superconductivity in Oxides Before 1986.- 2. Phases of the Systems A-La-Ca-Cu-O and A-Y-Ca-Cu-O (A = Ca, Sr, Ba): Structural Aspects.- 2.1 Copper Chemistry in Oxides: Oxidation States and Coordination.- 2.2 The Ternary Systems La-Cu-O and A-Cu-O (A = Ca,Sr,Ba).- 2.3 The Pseudoternary Systems A-La-Cu-O (A = Ca,Sr,Ba).- 2.3.1 Phases with Oxygen-Deficient Perovskite Structures.- a) BaLa4Cu5O13+?.- b) La8?xSrxCu8O20.- c) La3Ba3Cu6O14 and LaBa2Cu3O7??.- 2.3.2 The Intergrowths Between Perovskite and Rock-Salt-Type Structures.- a) The Oxides La2?xAxCuO4?x/2+?.- b) The Oxides La2?xA1+xCu2O6?x/2+?.- c) La4?2xBa2+2xCu2?xO10?2x.- 2.4 The Pseudoternary System Y-Ba-Cu-O.- 2.4.1 The Orthorhombic 92K Superconductor YBa2Cu3O7??.- 2.4.2 The Tetragonal Phases YBa2Cu3O7??.- 2.4.3 Problems of Microtwinning in the Orthorhombic YBa2Cu3O7??.- 2.4.4 The "Green Phase" Y2BaCuO5.- 2.4.5 Other Phases of the System Y-Ba-Cu-O.- 2.5 The Systems Ln-Sr-Cu-O (Ln ? La).- 3. Electron Transport Properties Connected with Oxygen Nonstoichiometry.- 3.1 Electron Transport Properties in Cuprates Related to the Perovskite: General Considerations.- 3.2 Oxides with the K2NiF4-Type Structure.- 3.2.1 La2CuO4.- a) "Normal" Properties.- b) Superconducting Properties.- 3.2.2 The Oxides La2?xAxCuO4?x/2+? (A = Ba, Ca, Sr).- a) Electron Transport Properties Above 77 K.- b) Superconducting Properties.- 3.2.3 Substitutions for Lanthanum in the Superconducting Oxide La1.8Sr0.2CuO4?y.- a) Rare-Earth Substitutions.- b) Bismuth Substitution.- 3.2.4 Other Cuprates with the K2NiF4 Structure.- 3.3 Oxides with the Oxygen-Deficient Sr3Ti2O7-Type Structure.- 3.3.1 The Oxides La2?xA1+xCu2O6?x/2+? (A = Sr, Ca).- 3.3.2 The Oxides Ln2?xSr1+xCu2O6?x/2.- a) Ln = Pr, Nd; x = 0.14.- b) Ln = Eu, Sm, Gd; x = 0.9.- 3.4 Oxides with the Oxygen-Deficient Perovskite Structure.- 3.4.1 Nonsuperconducting Oxides.- a) LaCuO3.- b) BaLa4Cu5O13+? and La8?xSrxCu8O20??.- c) Ba3La3Cu6O14+?.- 3.4.2 Superconducting Oxides: Properties of YBa2Cu3O7??.- a) The "Stoichiometric" Oxide.- b) Influence of the Oxygen Nonstoichiometry.- c) Substitution for Yttrium and Barium.- 4. Substitutions in La2CuO4-Type and YBa2Cu3O7-Type Superconductors.- 4.1 Substitution on the Rare-Earth Sites.- 4.1.1 La2CuO4-Type Oxides.- 4.1.2 YBa2Cu3O7-Type Oxides.- 4.2 Substitution on the Copper Sites.- 4.2.1 La2CuO4-Type Oxides.- 4.2.2 YBa2Cu3O7-Type Oxides.- a) Nickel Substitution.- b) Iron Substitution.- c) Other Transition Element Substitutions.- d) Other Substitutions.- 4.3 Substitutions on Other Sites.- 4.3.1 Substitution for Barium.- 4.3.2 Fluorination of YBa2Cu3O7??.- 5. Bismuth, Thallium and Lead Superconducting Cuprates.- 5.1 Bismuth Alkaline-Earth Superconducting Cuprates.- 5.2 Thallium Alkaline-Earth Superconducting Cuprates.- 5.3 Lead Alkaline-Earth Superconducting Cuprates.- 5.4 Layered Cuprates Involving Double Fluorite-Type Layers.- 5.5 Structural Relationships.- 6. Extended Defects in Superconducting Oxides: High-Resolution Electron Microscopy.- 6.1 YBa2Cu3O7-Type Superconductors: Ordering in the Perovskite Framework.- 6.1.1 YBa2Cu3O7??.- a) HREM Images.- b) 92 K Orthorhombic Superconductor (0???0.1).- c) Order-Disorder Phenomena: The 60 K Superconductor YBa2Cu3O7?? (0.37???0.45).- d) Nonsuperconducting Tetragonal Phases YBa2Cu3O7??.- e) Ordering of Oxygen Vacancies: Concluding Remarks.- 6.1.2 La Ba3?xCu3O14+y Phases.- a) LaBa2Cu3O7??.- b) La3Ba3Cu6O14+y.- 6.2 Nature and Ordering of the Stacked Layers: Intergrowth Mechanisms.- 6.2.1 Structural Considerations for HREM Studies.- 6.2.2 The Bismuth Family.- 6.2.3 Thallium Families: The Classical Defects.- a) Perovskite Layers.- b) Rock-Salt-Type Layers.- 6.2.4 The Nonsuperconducting TlBa2NdCu2O7: A New Mechanism.- a) Classical Deffects.- b) Variations in the Fluorite-Type Layers.- 6.2.5 Lead Oxides.- 6.2.6 The Rare Earth Oxides.- 6.3 Layer Interconnections.- 6.4 Extra Spots in ED Patterns: An Amazing Variety.- 6.4.1 Substituted Bismuth Oxides.- 6.4.2 Thallium Oxides.- 6.4.3 Lead Oxides.- 6.5 Domains and Boundaries.- 7. Irradiation Effects in the High-Tc Superconducting Oxides.- 7.1 Radiation Damage in Solids.- 7.1.1 Electronic and Nuclear Stopping Powers.- 7.1.2 Material Modifications.- a) Electronic Energy Loss Effects.- b) Nuclear Energy Loss Effects.- 7.2 Radiation Damage by Electrons and Fast Neutrons in Copper Oxide Superconductors.- 7.2.1 Defect Structures Produced by Electron Irradiation.- 7.2.2 Changes Induced by Fast Neutron Irradiation.- 7.3 Phase Transformations Induced by Fast Heavy Ions in the High-Tc Copper Oxides.- 7.3.1 Improvement of Tc in the Grain Surface Superconductor La2CuO4.- 7.3.2 Heavy-Ion-Induced Changes of Superconducting and Normal Properties of Polycrystalline Ceramics YBa2Cu3O7?? and Bi2Sr2CaCu2O8.- 7.3.3 Ion Implantation Effects in Thin Films of Copper Oxide Superconductors.- 7.4 Conclusions.- 8. Concluding Remarks.- 8.1 Low Dimensionality of the Structure.- 8.2 Mixed Valence of Copper and Hole Delocalization.- 8.3 The Model of Copper Disproportionation.- 8.4 Role of the Lone Pair Cations and of the Alkaline Earth Elements.- References.