G.W. Webb

Erratum: Cold‐working Nb3Al in the bcc structure and then converting to the A‐15 structure

It is possible to quench gram quantities of stoichiometric Nb3Al in the ductile body‐centered cubic structure which can be cold worked. Later annealing converts this material to the brittle superconducting A‐15 structure.

Superconducting, metallurgical and synthesis properties of Nb 3 Ga

We present a review of the superconducting, metallurgical and synthesis properties of Nb 3 Ga which are important for its potential application. The superconducting properties to be discussed are T c , H c2 (T) and the dc critical current J c (H). Special metallurgical features of the Nb-Ga system which put severe constraints on synthesis techniques of potential practical importance for this material are discussed. Superconductivity data for materials synthesized by the techniques of quenching and annealing, chemical vapor deposition and vacuum co-evaporation are reviewed. Recent results on the effects of radiation damage and its recovery by annealing are reviewed.

Critical currents in A-15 structure Nb3Al converted from cold-worked bcc structure

Nb3Al prepared in the ductile bcc phase by quenching, followed by mechanical working, followed by conversion to the A‐15 structure is found to carry currents above 109 A/m2 in fields near 20 T. These critical currents are comparable to those found in Nb3Ge and V3Ga, the closest competing materials for use in high fields. Further enhancement of Jc is possible if thermal treatments are optimized.

Mechanical and superconducting properties of Nb 3 Al

Nb 3 Al can be quenched from under a solidus into the low T c ductile BCC structure. In the BCC structure a variety of cold working operations can be performed on it without fracture. Later annealing converts this material to the high T c brittle A-15 structure.

Superconductivity and the d-Shell

The various isotope effects on the superconducting transition temperature of Mo2B and W2B have been measured. Together with resistivity data they indicate that the d-shell forms a highly stable electron configuration for molybdenum and tungsten. This leads to an understanding of high superconducting transition temperatures.

Lattice dynamics of the A 15 compound Nb 3 Sb

The phonon dispersion curves of Nb/sub 3/Sb have been studied by inelastic neutron scattering. All the branches have been determined in the main symmetry directions and the results are analyzed with Born--von Karman models of different complexity. A model with general forces up to the eighth-nearest neighbors gives excellent agreement with experiment. However, a rather good description of the dispersion curves is obtained with a model including axially symmetric forces up to the third-nearest neighbors, which indicates that these interactions are dominant. Temperature effects were found to be very small. Additional experiments were performed on polycrystalline samples to determine directly the phonon density of states. Our results obtained on Nb/sub 3/Sb are compared with the available phonon data on Nb/sub 3/Sn.

Critical currents in Nb 3 Ge based pseudobinaries

We have prepared Nb 3 Ge, Nb 3 Ge 1-x Ga x and Nb 3 Ge 1-x Sn x on heated alumina substrates using CVD. Midresistive transitions were up to 21K and transition widths were as low as 0.3K. Critical currents were measured to 22 Tesla at temperatures from 4.2K to 19K. Effective upper critical fields B* c2 were measured by extrapolating J\min{c}\max{V2} vs B data. Preliminary data show that for small Ga additions, B* c2 increased above the value at x=0. Flux pinning forces vs reduced field b=B/B* c2 do not obey scaling laws, which we explain as being due to inhomogeneous material having a distribution of T c and B c2 values.

Lattice dynamics of the A15 compound Nb/sub 3/Sb

The phonon dispersion curves of Nb/sub 3/Sb have been studied by inelastic neutron scattering. All the branches have been determined in the main symmetry directions and the results are analyzed with Born--von Karman models of different complexity. A model with general forces up to the eighth-nearest neighbors gives excellent agreement with experiment. However, a rather good description of the dispersion curves is obtained with a model including axially symmetric forces up to the third-nearest neighbors, which indicates that these interactions are dominant. Temperature effects were found to be very small. Additional experiments were performed on polycrystalline samples to determine directly the phonon density of states. Our results obtained on Nb/sub 3/Sb are compared with the available phonon data on Nb/sub 3/Sn.