Superconducting Thin Films, Composites and Junctions
Abstract
The Nb-Al system has been used as a model system to study the phase transformation in metastable alloys by using the superconductivity of the A15 phase to determine the composition with the highest Tc, and the lattice constant to determine the average composition. By depositing Nb-Al in a phase spread orientation onto substrates at C, the bcc structure has been extended to about 40 at % (well above the equilibrium 9%). Subsequent annealing experiments transformed the bcc phase to A15. It was found that stoichiometric Nb3Al could be formed in the A15 phase well above the concentration of the Al at equilibrium which is 22%, when the slopes of the free energy curves of the respective phases are equal. Thus the particular shape of the (free) energy curves is important and can determine the composition of the precipitated phase. Nb-Sn-Ga alloys were prepared and studied as model systems to investigate the influence of third element additions on the normal and superconducting properties of alloyed Nb-3Sn phases. In spite of a decrease in the density of states at the Fermi level with increasing Ga content and upper critical field, Bc2 was found to increase. Bc2 maximized at 1 to 1.5 at % Ga for reaction temperatures at 700 C. High critical fields up to 31.5 T (at T=4.2K) have been achieved. (rrh)
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 30, 1984
- Accession Number
- ADA215334
Entities
People
- Theodore H. Geballe
Organizations
- Stanford University