17 research outputs found
Conductive Buffer Layers and Overlayers for the Thermal Stability of Coated Conductors
We analyze fundamental issues related to the thermal and electrical stability
of a coated conductor during its operation. We address the role of conductive
buffer layers in the stability of Ni-based coated conductors, and the effect of
a metallic cap layer on the electrical properties of Ni alloy-based
superconducting tapes. For the first case we report on the fabrication of a
fully conductive RABiTS architecture formed of bilayers of conductive oxides
SrRuO3 and LaNiO3 on textured Ni tapes. For the second case we discuss
measurements of current-voltage relations on Ag/YBa2Cu3O7-d and Cu/Ag/
YBa2Cu3O7-d prototype multilayers on insulating substrates. Limitations on the
overall tape structure and properties that are posed by the stability
requirement are presented.Comment: 4 pages, 5 figure
Aligned crystallite powder of NdFeAsOF: magnetic hysteresis and penetration depth
We report the basal-plane critical current and superfluid density of
magnetically aligned NdFeAsOF powder. This sample has
individual crystallite grains permanently oriented with their c axis along the
external field. Magnetic irreversibilities at high field suggest strong flux
pinning of basal-plane critical currents, with monotonic field dependence and
no evidence of the "fishtail" effect. The small particles provide a sensitive
indicator of \textit{dc} flux penetration, and allow analysis of the
temperature dependence of plane London penetration depth
, which is quadratic at low . This feature may not
necessarily be due to the nodes in the gap, but may be rather a sign of a
strong pair-breaking. A quantitative determination of the absolute magnitude of
is hindered by the need for accurate knowledge of the
particle size distribution.Comment: 6 pages, 6 figure
Microstructure and In Situ Observations of Undercooling for Nucleation of β-Sn Relevant to Lead-Free Solder Alloys
Difficult nucleation of β-Sn during solidification of tin and tin-based lead-free solder alloys can result in high degrees of undercooling of the liquid prior to solidification. The undercooling can produce solder joints with large grains, anisotropic behavior, and undesirable mechanical properties. This paper describes our examination of the amount of undercooling of tin on both graphite (non-wetting) and copper (wetting) surfaces using in situ x-ray diffraction. The microstructure was further characterized by optical microscopy, scanning electron microscopy, and electron backscattering diffraction imaging microscopy. Undercoolings as high as 61°C were observed for Sn solidified on graphite, while lower undercoolings, up to 30°C, were observed for Sn solidified on copper. The microstructure of the high purity Sn sample solidified on graphite showed very few grains in the cross-section, while the commercially pure Sn sample solidified with only one grain and was twinned. Tin solidified on copper contained significant amounts of copper in the tin, intermetallic phase formation at the interface, and a eutectic microstructure