Formation of the A15 phase in thin-film Nb-Al diffusion couples

Journal Article · Wed Jan 14 23:00:00 EST 1987 · J. Appl. Phys.; (United States)

DOI:https://doi.org/10.1063/1.338955· OSTI ID:6974890

Gavaler, J R; Braginski, A I; Greggi, J; Schulze, K

Single-crystal and polycrystalline thin-film Nb-Al diffusion couples have been prepared by evaporation at pressures of 10/sup -11/--10/sup -10/ Torr. Sapphire, single-crystal MgO, polycrystalline Al/sub 2/O/sub 3/, and polycrystalline Nb were used as substrates. These couples were annealed in situ at temperatures between T = 780 and 950 /sup 0/C for 30 min, in order to study the formation of the A15 phase. Based on resistivity data, between 800 and 880 /sup 0/C, the A15 phase was formed only on oxide substrates. The relative A15 content was higher in polycrystalline couples than in single-crystal couples. Between 880 and 950 /sup 0/C the A15 phase was also obtained in couples deposited on Nb substrates. X-ray data confirmed that the temperature of the A2 (bcc) to A15 structure transformation was lower in couples where the Nb-Al solid solution was in contact with an oxide substrate. X-ray photoelectron spectroscopy indicated the occurrence of surface reactions between the oxide substrate and Nb or Al. Auger depth profiles of the Nb/Al ratio were similar in couples on all substrate types studied and could not be correlated with A15 phase formation. The A15 phase having T/sub c/'s corresponding to the upper (Al-rich) boundary of the A15 phase stability field appeared to form locally at defects, grain boundaries, and other imperfections. Alternative explanations of the experimental findings are discussed.

• Research Organization: Westinghouse RandD Center, Pittsburgh, Pennsylvania 15235
• OSTI ID: 6974890
• Journal Information: J. Appl. Phys.; (United States), Journal Name: J. Appl. Phys.; (United States) Vol. 61:2; ISSN JAPIA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360104* -- Metals & Alloys-- Physical Properties
656100 -- Condensed Matter Physics-- Superconductivity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALLOYS
ALUMINIUM ALLOYS
AUGER ELECTRON SPECTROSCOPY
CRYSTAL-PHASE TRANSFORMATIONS
DIFFUSION
DISPERSIONS
ELECTRICAL PROPERTIES
ELECTROMAGNETIC RADIATION
ELECTRON SPECTROSCOPY
FABRICATION
FILMS
IONIZING RADIATIONS
MIXTURES
NIOBIUM ALLOYS
PHASE TRANSFORMATIONS
PHOTOELECTRON SPECTROSCOPY
PHYSICAL PROPERTIES
RADIATIONS
SOLID SOLUTIONS
SOLUTIONS
SPECTROSCOPY
SUPERCONDUCTING FILMS
THIN FILMS
VERY HIGH TEMPERATURE
X RADIATION