Chemical Aspects of New Superconducting Materials and Fabrication Techniques

Abstract

Significant progress has been made in recent years in thermonuclear research. For continued progress leading to economically attractive fusion reactors the use of large superconducting magnets for the heating and confinement of plasmas appears to be necessary. Similarly, superconducting transmission line networks will be required for the distribution of power from large fusion reactors. For each application, the “lbest” superconducting material may exhibit different properties, but for both uses, the search for new and better superconducting materials and fabrication methods will be a continuing requirement. Theories of superconductivity are very successful in explaining properties of the superconducting state and the origin of superconducting electron pairs, but up to the present have been of no value in guiding the search for better superconducting materials. Progress has been made through the use of empirical correlations of normal state properties with superconducting transition temperatures. These includes average number of valence electrons per atom versus T_c; valence electron density versus T_c; lattice parameter or M-M distances (M = transition metal) versus T_c in special crystal structures; and variations of these approaches with attempts to include lattice vibration properties. Recent work has demonstrated that stoichiometry and ordering are most important and suggests that existing empirical correlations may not be useful in the search for new superconductors. New developments indicate that many high temperature superconductors will be f ound in complex ternary and quaternary systems.

Innovations in fabrication methods promise that the highest T_c and critical field materials may soon be fabricated in the form of relatively ductile multifilament composite wires. This will contribute greatly to the application of superconducting technology in controlled thermonuclear reactors.