John W. Schweitzer

Superconductivity in yttrium-terbium-barium-copper oxide

Abstract The effect of terbium substitutions for yttrium in Y1Ba2Cu3O7−δ on the superconducting transition temperature, the resistivity, and the lattice constants are reported in this study. Samples of Y1−xTbxBa2Cu3O7−δ for ¢ = 0, 0.04, 0.08, 0.12, 0.16 were prepared by the nitrate-citrate gel method. The transition temperature did not change with ¢ in this composition range.

Narrow Band Magnetism of Alloys

The purpose of these lectures is to discuss the use of the coherent potential approximation (CPA) for the study of disordered magnetic alloys from the itinerant point of view. The CPA has contributed significantly to the theory of concentrated non-magnetic alloys described by one-electron Hamiltonians. For these alloys the CPA scheme gives a practical treatment of the disorder which yields reasonable results for arbitrary concentrations and scattering strengths. The extension to magnetic alloys necessarily involves many body effects which have yet to be systematically studied. At the present stage one relies on highly simplified models and straightforward extensions of the CPA as formulated in the context of one-electron Hamiltonians. While this does not permit a detailed confrontation of theory and experiment, the studies can be made tractable and the satisfactory features and defects can be recognized.