Surface resistance of superconducting A15 niobium-tin films at 8. 6 GHz

Thesis/Dissertation · Thu Jan 01 04:00:00 EST 1987

OSTI ID:7202228

Allen, L H

A calorimetric technique for measuring the temperature dependence of the surface resistance of high-T/sub c/ superconducting thin films at 8.6 GHz was developed. The technique was applied to study electron-beam, co-deposited films of the A15 phase of Nb-Sn with the goal of optimizing the microwave losses of the material. In addition, films of sputtered Nb-Sn, Nb-Zr alloy, and Nb-N were also studied. For the evaporated Nb-Sn films, carefully controlled deposition temperatures of greater than 900 C are necessary to obtain the lowest losses. A sharp transition is observed for stoichiometric material (25% Sn), but for the understoichiometric compositions the transitions are wider, yielding excessive losses in the material. Films prepared by magnetron sputtering behave similarly. A procedure, phase-locking, for preparing the stoichiometric composition, which does not require exact control of the deposition rates was developed and successfully demonstrated with the evaporated films. The experimental data are compared with two theoretical predictions: one of the superconducting state based on the BCS theory and a normal-state calculation in the classical skin-depth limit. When the residual losses (10-micro-ohms) are subtracted form the data, the behavior predicted for the superconducting state is observed. The normal-state losses, however, are anomalously large for the Nb-Sn films.

• Research Organization: Stanford Univ., CA (USA)
• OSTI ID: 7202228
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360104* -- Metals & Alloys-- Physical Properties
ALLOYS
BETA-W LATTICES
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DEPOSITION
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
FILMS
NIOBIUM ALLOYS
PHYSICAL PROPERTIES
STOICHIOMETRY
SUPERCONDUCTING FILMS
SURFACES
TEMPERATURE DEPENDENCE
THIN FILMS
TIN ALLOYS