Showing papers by "Thomas Henry Tiefel published in 1987"

Composite electrical interconnection medium comprising a conductive network, and article, assembly, and method

Abstract: An electrical interconnection medium is made as a composite of electrically conducting, magnetic particles in a nonconductive matrix material. Particles are magnetically aligned into a network which extends in at least two dimensions as, e.g., in a sheet or layer medium. A layer medium may further include additional, larger conductive particles which may be magnetically aligned into columns extending the thickness of the medium; typically, in this case, the medium serves as an anisotropically conductive medium in the direction of the columns, with slight in-plane conductivity imparted by the network aiding the dissipation of electrostatic charge.

Fabrication of oxide superconductors by melt growth method

Abstract: Superconductive oxide bodies such as wires, ribbons, rods, and other bulk bodies can be fabricated by a process that comprises melting precursor material, cooling at least of the melt such that a solid body of a desired shape results, and heat treating the solid body in an oxygen-containing atmosphere The precursor material exemplarily is in the form of pressed superconductive oxide powder The re-solidified superconductive material is relatively dense, typically textured, with relatively large grain size, and has improved properties, eg, higher critical current density An exemplary technique for melting of the precursor material is zone melting

Superconducting Properties of YBa2Cu3O7-δ Doped with Various Metals and Oxides

Abstract: The interactions of YBa2Cu3O7-δ type high Tc superconductors with other metals and oxides are of significant technical importance because of the need for i) proper stabilizing normal metal for composite superconductor wire, ii) nonreactive crucible materials for melt processing or crystal growth, and iii) suitable nonpoisonous substrate materials for thin film/thick film superconducting devices. For these reasons, and also for the purpose of exploring possible improvements in Tc, Jc and mechanical properties, the effects of various metal and oxide additions (1–40% by weight) have been investigated. It is shown that many of the elements in the periodic table deteriorate the superconducting properties to a various degree ranging from a broadened transition or reduced Tc to a complete elimination of the superconducting behavior. However, silver, gold and cadmium were relatively benign or slightly improved the properties. These benign materials have potential for practical application in superconducting composites.

Critical Current Density of the YBa2Cu3O7-δ Superconductor as Affected by Microstructuralxontrol

Abstract: The recent discovery of the YBa2Cu3O7-δ type high Tc superconductors stimulated worldwide R&D interest in this field. However, the relatively low critical current density (Jc) in the polycrystalline, bulk superconductors (as well as its significant deterioration in weak magnetic fields) has been a major roadblock to the rapid technical advancement toward applications. In this paper, we investigated the effect of processing and microstructural control on Jc of the superconductor. Improved Jc values of -3100 A/cm2 at 77K with somewhat reduced field dependence have been obtained through appropriate microstructural modifications.

Effect of Temperature Cycles on the Critical Current Density of YBa2Cu3O7-δ

Abstract: The transport Jc of the polycrystalline YBa2Cu3O7-δ superconductor seems to be dominated by weak links between high Jc regions as evidenced by low Jc values and their strong field dependence. The possible effects of thermal expansion-contraction and the tetragonal-orthorhombic transformation on the weak links and the Jc values were investigated by repeated thermal cycling of sintered pellets between -196°C and various high temperatures (600–850°C) using a furnace heating and cooling in an oxygen atmosphere. While more than a five-fold decrease in Jc from -400 to -70 A/cm2 (at 77K in zero field) is observed after 5 temperature cycles between -196’C and 850°C, only a slight decrease (to -370 Atm2) is noticed after 5 cycles between -196*C to 600°C, the temperature span of which is not all that much smaller than the former cycles. Transmission electron microscopy analysis clearly indicates that the drastic deterioration in Jc by repeated phase transformation is caused by increased amount of microcracks on (001) basal planes near the grain boundaries. The results will be discussed in terms of the large thermal expansion anisotropy of this layer-structured compound.