PROGRAM TITLE: Superconductivity

Principal investigator(s):

NIST Staff:

Designated Project Leader:

Vanderah, Terrell A.
Mailing Address:
NIST
Materials (223), A256
Gaithersburg, MD 20899
Telephone: (301) 975-5785
Fax Number: (301) 990 8729
E-mail Address: terrell@credit.nist.gov

Other NIST Principal investigator(s):

Wong-Ng, Winnie
Mailing Address:
NIST
Materials (223), A256
Gaithersburg, MD 20899
Telephone: (301) 975-5791
Fax Number: (301) 990-8729

Cook, Lawrence P.
Mailing Address:
NIST
Materials (223), A256
Gaithersburg, MD 20899

Drews, Andrew R.
Mailing Address:
NIST
Materials (223), A256
Gaithersburg, MD 20899
Telephone: (301) 975-5786
Fax Number: (301) 990-8729

Technical Objectives:

Conduct phase-equilibria studies of superconducting materials with emphasis on regions pertinent to the processing of bulk conductors. Determine the primary crystallization field of the bismuth- strontium-calcium-copper oxide "2212" superconductor in air and investigate the effect of silver impurities. Investigate phase relations of thallium 1223-type superconductors with emphasis on melting behavior and associated thallia vapor pressures. Conduct high-temperature X-ray powder diffraction studies of Pb-BiSCCO "2223" wire precursor material as a function of oxygen partial pressure.

Accomplishments

The approximate primary crystallization field of the BiSCCO "2212" superconductor has been determined in air and encompasses a mole fraction compositional range of (20 to 42)% BiO_1.5, (15 to 35)% SrO, (2 to 25)% CaO, and (20 to 43)% CuO. Ag enters the melts at saturation levels of (6 to 8)% and depresses the solidus by as much as 26^oC. Cu also substitutes into Ag, lowering its melting temperature. The 2212 BiSCCO superconductor melts incongruently to liquid plus alkaline-earth-rich phases and exhibits a eutectic at 825^oC (Bi:Sr:Ca:Cu = 41.7:16.1:22.3:19.9). Melt compositions and associated thallia vapor pressures have been determined for three different thallium 1223-type superconducting compositions; thallia vapor pressures were found to be highly variable with substituent type. In contrast, the compositions of the melts were relatively insensitive to substituent-type and characteristically Cu-, Pb-, and Bi- rich and alkaline-earth-poor. High-temperature X-ray diffraction studies of Pb-BiSCCO 2223 wire precursor were conducted on silver foil under varying oxygen partial pressure and at different heating rates. Melting, recrystallization, and orientation phenomena were found to be markedly dependent on heating rate, the presence of silver, and oxygen partial pressure.

Outputs:

"Melting Equilibria of the Bi-Sr-Ca-Cu-O (BSCCO) System in Air. I. the Primary Crystallization Phase Field of the "2212" Phase and the Effect of Ag Addition", W. Wong-Ng, L.P. Cook, and F. Jiang. In final preparation.

"Melting Equilibria of the Ba-Y-Cu-O System in the Vicinity of the Ba₂YCu₃O_6+x Phase Field", W. Wong-Ng and L.P. Cook. Submitted to Journal ACerS.

"Comparative Melting and Vaporization Behavior of Doped Thallium 1223 Phases: Preliminary Results in Oxygen", L.P. Cook and W. Wong-Ng. Submitted to NIST Journal of Research.

"High-Temperature X-ray Studies of Growth and Texturing of Bi-2223 on Silver", A.R. Drews, J.P. Cline, T.A. Vanderah, and K. Salazar. In final preparation.