Superconductivity in Ternary Compounds I: Structural, Electronic, and Lattice Properties

ISBN-13: 9783642818707 / Angielski / Miękka / 2011 / 286 str.

O. Fischer; L. B. Maple

Opis

The structural. electronic and lattice properties of superconducting ternary com pounds are the subject of this Topics volume. Its companion volume (Topics in Cur rent Physics. Volume 34) deals primarily with the mutual interaction of supercon ductivity and magnetism in ternary compounds. These two volumes are the culmination of a project. started nearly two years ago. that was inspired by the intense re search effort. both experimental and theoretical. then being expended to explore and develop an understanding of the remarkable physical properties of ternary super conductors. Research activity on this subject has increased in the meantime. The interest in ternary superconductors originated in 1972. when B.T. Matthias and his co-workers first discovered superconductivity in several ternary molybdenum sulfide compounds that had been synthesized in 1971 by R. Chevrel. M. Sergent. and J. Prigent. The superconducting critical temperature Tc of one of the compounds. PbMo S was reported to be 15 K. This value is sufficiently high that there was g 6 (and still is) reason to expect that other ternary compounds would be found with superconducting transition temperatures rivaling those of the A15 compounds. of which Nb Ge has the record high Tc of 23 K. The interest in ternary superconductors 3 received further impetus when several of the ternary molybdenum sulfides were found to have exceptionally high upper critical magnetic fields. some of them in the neighborhood of 50 Tesla or more. An immense amount of research on ternary molybdenum chalcogenides then followed."

Spis treści

1. Superconducting Ternary Compounds: Prospects and Perspectives.- 1.1 Introduction.- 1.2 The Ternary Materials.- 1.2.1 The Ternary Molybdenum Chalcogenides (Chevrel Phases).- 1.2.2 The Ternary Rhodium Borides.- 1.2.3 Other Ternary Compounds.- 1.3 Concluding Remarks.- References.- 2. Chemistry and Structure of Ternary Molybdenum Chalcogenides.- 2.1 Overview.- 2.2 Preparation and Characterization.- 2.2.1 Preparation.- 2.2.2 Characterization: Chalcogenides MxMo6X8.- 2.3 Crystal Structure.- 2.3.1 Structural Parameters of MxMo6X8 Compounds.- 2.3.2 Crystal Structure.- 2.3.3 The Triclinic Phase.- 2.4 Relations Between Structure and Properties.- 2.4.1 Stabilization of Mo6S8.- 2.4.2 Mixed Anion: Substitution of Halogen for Chalcogen.- 2.4.3 Substitution on the Octahedral Cluster (Mo, Me)6 (Me = Nb, Ta, Re, Ru, Rh).- 2.4.4 Chalcogen-Chalcogen Substitution (S, Se, Te).- 2.4.5 Substitution of Oxygen for Sulphur.- 2.4.6 Addition of MMx? and Substitution of (M, M?) on an Element in the Channels.- 2.5 New Ternary Compounds Resulting from Linear Condensation of the Octahedral Mo6 Clusters.- 2.5.1 A New Cluster Mo9 in a Mo9X11 Unit (X = S, Se).- 2.5.2 A New Cluster Mo12 in a Mo12X14 Unit (X = S).- 2.5.3 New One-Dimensional Cluster (Mo6/2)?1 in the (Mo6/2X6/2)?1 Unit (X = S, Se, Te).- 2.6 Conclusion.- Appendix: Tables.- References.- 3. Structure and Bonding of Ternary Superconductors.- 3.1 Introductory Comments.- 3.2 Ternary Molybdenum Chalcogenides MMo6X8 (M: Metal, X: Chalcogen).- 3.2.1 Structure.- 3.2.2 Occurrence.- 3.2.3 Bonding.- 3.3 Ternary Molybdenum Chalcogenides Built Up by Condensed Mo3nX3n+2 Units (X = S, Se, Te).- 3.3.1 Structure.- 3.3.2 Occurrence.- 3.3.3 Bonding.- 3.4 Ternary Borides MT4B4 (M: Metal, T: Transition Element).- 3.4.1 CeCo4B4 Type (tP18, Tcmax = 12 k)3.- 3.4.2 LuRu4B4 Type (tI72, Tcmax = 11 K).- 3.4.3 LuRh4B4 Type (oC108, Tcmax = 6.3 K).- 3.4.4 NdCo4B4 Type (tP18, Tc < 4 K).- 3.4.5 Bonding of the MT4B4 Borides.- References.- 4. Metallurgy and Structural Transformations in Ternary Molybdenum Chalcogenides.- 4.1 Preparation Methods and Stoichiometry.- 4.1.1 Sintering.- 4.1.2 RF Melting Under High-Pressure Argon.- 4.1.3 Stoichiometry.- 4.2 High-Temperature Phase Fields in Some Selected Systems.- 4.2.1 The Binary System Mo-S.- 4.2.2 The System CuxMo6S8.- 4.2.3 The System CuxMo6Se8.- 4.2.4 The System Pb-Mo-S: PbxMo6S8?y or PbxMo6S8?.- 4.2.5 The Systems Ag-Mo-S, Ag-Mo-Se, Pb-Mo-Se, Sn-Mo-Se.- 4.3 Low-Temperature Relationships in CuxMo6S8 and CuxMo6Se8.- 4.3.1 Experimental Methods.- 4.3.2 The System CuxMo6S8.- 4.3.3 CuxMo6Se8.- 4.4 The Type of Formation of the Triclinic Phase in Ternary Molybdenum Chalcogenides.- 4.4.1 Existence of a Miscibility Gap in the Rhombohedral Phase.- 4.4.2 “Small” M Atoms: M = Ni, Zn, Co, Cr, Mn, Ti, V, Fe.- a) The Systems NixMo6Se8 and NixMo6S8.- b) The Systems ZnxMo6Se8 and ZnxMo6S8.- c) Ternary Molybdenum Chalcogenides with M = Co, Cr, Mn, Ti, V and Fe.- 4.4.3 “Large” M Atoms.- 4.5 Mechanism of Structural Transformations in Ternary Molybdenum Chalcogenides.- 4.5.1 The Delocalization of the M Atom.- 4.5.2 The Mechanism of Structural Transformations in MxMo6S8 Compounds (M = Cu, Fe,...).- a) Intrasite Mobility.- b) Metallurgical Arguments: Intersite Mobility.- 4.5.3 The Mechanism of Structural Transformations in Compounds with “Large” M Atoms.- 4.6 Superconductivity and Structural Transformations in Ternary Rhombohedral Compounds.- References.- 5. Thin-Film Ternary Superconductors.- 5.1 Preliminary Comments.- 5.2 Preparation and Structure.- 5.3 Critical Fields.- 5.4 Critical Currents.- 5.5 Electronic Properties.- 5.6 Final Statements and Conclusions.- References.- 6. Band Structures of MxMo6X8 — and M2Mo6X6-Cluster Compounds.- 6.1 General Considerations.- 6.2 Input to the Band-Structure Calculations.- 6.2.1 Crystal Structure.- 6.2.2 Atomic-Sphere Potentials.- 6.3 One-Electron States of a Single Mo6X8 Cluster.- 6.3.1 The X p States of a Regular Cube.- 6.3.2 The Mo d States of a Regular Octahedron.- 6.3.3 The d Bond Orbital of a Regular Octahedron.- 6.3.4 Mo-X Hybridization.- 6.3.5 Real Clusters.- 6.4 Energy Bands of Chevrel Phases.- 6.4.1 Gross Features of the Densities of States.- 6.4.2 Energy Bands Along the $$\bar 3$$-Axis from ? to R.- 6.4.3 The t1u and egd Levels at ?.- 6.4.4 The t2gd and egd Levels at R.- 6.4.5 The Conduction Band.- 6.4.6 Relation to Structural Properties.- 6.5 Energy Bands of Chain Compounds.- 6.5.1 General Features of the Energy Bands.- 6.5.2 Interpretation of the d-Band Structure.- 6.5.3 Physical Properties.- References.- 7. Phonons in Ternary Molybdenum Chalcogenide Superconductors.- 7.1 Preliminary Comments.- 7.2 The Molecular-Crystal Model and Lattice Heat Capacity.- 7.3 Phonon Spectra from Inelastic Neutron Scattering.- 7.3.1 The Theory of the Technique for Polycrystalline Samples.- 7.3.2 Experimental Neutron Scattering Results.- 7.4 A Simple Force-Constant Model for the Lattice Dynamics of Chevrel-Phase Compounds.- 7.4.1 Theoretical Considerations.- 7.4.2 Calculated Dispersion Curves.- 7.4.3 Calculated Phonon Densities of States.- 7.4.4 Calculated Neutron-Weighted Densities of States Comparisons.- 7.4.5 Relationship to Mössbauer Effect.- 7.4.6 Calculated Moments of the Phonon Spectrum.- 7.4.7 Calculated Lattice Entropy and Heat Capacity.- 7.5 Inelastic Neutron Scattering Experiments on Single Crystals.- 7.6 Relationship of the Phonon Spectrum to the Electron-Phonon Interaction.- 7.7 Summary.- References.- 8. Electron-Phonon Interaction in Chevrel-Phase Compounds.- 8.1 Introductory Remarks.- 8.2 Experiments on the Electron-Phonon Coupling.- 8.3 Theoretical Models for the Electron-Phonon Coupling.- 8.4 Isotope Effect of Tc in Mo6Se8 and SnMo6S8.- 8.4.1 The Isotope Effect.- 8.4.2 Sample Preparation.- 8.4.3 Results for the Isotope Effect Exponent.- 8.4.4 Discussion of the Measured Isotope Effect.- a) Mo6Se8.- b) SnMo6S8.- 8.5 Tunneling Spectroscopy on Cu1.8Mo6S8 and PbMo6S8.- 8.5.1 Tunneling Experiment.- 8.5.2 Junction Preparation.- 8.5.3 Results and Discussions.- 8.6 Conclusion.- References.