G.W. Hull

Epitaxial growth of high Tc superconducting Nb3Ge on Nb3Ir

Nb3Ir polycrystalline films with the A15 structure deposited on sapphire were used as substrates for the epitaxial growth of Nb3Ge because of the favorable lattice parameter match. The experimental results clearly show that epitaxial growth indeed occurs and helps to extend the range of homogeneity of the A15 phase up to 26.3 at.% Ge as compared with the thermodynamic equilibrium boundary at 19 at.% Ge. Furthermore, epitaxy results in a considerable rise in the superconducting transition temperature for Ge‐rich samples together with a reduction in the transition width.

Epitaxial growth of high T/sub c/ superconducting Nb/sub 3/Ge on Nb/sub 3/Ir

Nb3Ir polycrystalline films with the A15 structure deposited on sapphire were used as substrates for the epitaxial growth of Nb3Ge because of the favorable lattice parameter match. The experimental results clearly show that epitaxial growth indeed occurs and helps to extend the range of homogeneity of the A15 phase up to 26.3 at.% Ge as compared with the thermodynamic equilibrium boundary at 19 at.% Ge. Furthermore, epitaxy results in a considerable rise in the superconducting transition temperature for Ge‐rich samples together with a reduction in the transition width.

The occurrence of superconductivity in sulfides, selenides, tellurides of Pt-group metals☆

Superconductivity has been discovered in Pd compounds with Se and Te, in IrTe3 and in PtTe. The superconducting transition temperature of a Pd-Se alloy containing 85 to 87 at.% Pd is 0.66°K which is unusually high for its valence-electron concentration. A homogeneity range exists for the hexagonal B81-type compound PdTe and for the trigonal C6-type compound PdTe2. The results of the low temperature heat capacity measurements of PdTe and PdTe1.04 show that the large change in the transition temperature with composition is accompanied by a large change in the linear heat capacity coefficient, γ.

Ferromagnetism in metallic FexTaS2 (x≈0.28)

Single crystals of FexTaS2 (x≈0.28) are metallic, ferromagnetic (Tc=73±5 °K), and have a large coercive force of 55 kOe at 4.2 °K. Mossbauer measurements show the iron to be high‐spin Fe2+, with a distribution of hyperfine fields at low temperatures. Electron microscopic observations, together with these results, suggest the presence of iron clusters.

Crystal chemistry and superconductivity of pressure-induced phases in the InTe system

Abstract In the InTe system, a pressure-induced Nad-type phase exists in the region In 0.80 Te to In 1.5 Te. Superconductivity exists in the whole range, with the maximum transition temperature occurring for the stoichiometric InTe. A hypothesis previously given for the metallic behavior of this phase and the decrease of transition temperature on either side of the stoichiometric InTe is further elaborated. It is proposed that the transformation to the NaCl-type structure removes the structural constraint on electron transfer existing in the normal InTe. A method for calculating carrier concentration is given and it is shown that the superconducting transition temperature is a function of carrier concentration. At least two other pressure-induced InTe phases exist. One is In 3 Te 4 which becomes superconducting at 1·25–1·15°K. In 3 Te 4 has the anri-Sn 4 As 3 structure with seven atoms in a rhombohedral unit cell, all lying on the threefold axis. The positional parameters of the atoms and interatomic distances are given and the coordination shown to be related to that found in the NaCl-type structure. Pressure-temperature experiments on normal In 2 Te 3 indicate that a pressureinduced phase with this (or approximately this) composition cannot be obtained metastably without the presence of the In 3 Te 4 and an unidentified phase. The pressure-induced In 2 Te 3 phase has the well-known Bi 2 Te 3 structure and is closely related to the In 3 Te 4 structure. Superconductivity tests and X-ray diffraction investigation lead to the conclusion that the In 3 Te 4 phases occurring with the In 2 Te 3 phase are sometimes not stoichiometric and in such cases usually contain excess tellurium.

Superconducting properties of a liquid‐infiltration Nb‐Nb3Sn composite formed during a low‐temperature reaction

A powder metallurgy based ‘‘liquid‐infiltration’’ method was used to produce multifilamentary Nb‐Sn composite wires. New heat treatments combining relatively low‐temperature aging (≤800 °C) and long reaction time (≥ one day) were used to form superconducting A15 Nb3Sn. This heat treatment can be used for large conductors and practical magnets. Transmission electron microscopy studies revealed that the A15 Nb3Sn was formed in fine filaments which were embedded in the ductile Nb matrix. Small, equiaxed A15 grains extended across the reacted filament. A Tc onset of 17.9 K with a 0.4‐K transition width was obtained. Excellent high‐field critical currents, overall Jc’s ≥104 A/cm2 in a field of 18 T at 4.2 K, were achieved.

Multifilamentary Nb-Nb 3 Sn composite by liquid infiltration method: Superconducting, metallurgical, and mechanical properties

A rapid solid-liquid reaction mechanism has been used to form A15 Nb 3 Sn in the liquid-infiltration processed Nb-Sn wire. Small, equiaxed A15 grains across the fine reacted filaments of 0.2-1.0 μm thickness were revealed with the transmission electron microscopy studies. A uniform Sn concentration near the stoichiometry was found in the A15 region. High inductive T c s of 17.9K with sharp transition widths ( c s of 104A/cm2at 19T and 4.2K were achieved. Mechanical properties of the reacted wire are no worse than those of typical commercial bronze-process Nb 3 Sn conductors, and e irrev is slightly higher.

Multifilamentary superconducting (NbTa)-Sn Composite wire by solid-liquid reaction for possible application above 20 tesla

Abstract Nb alloyed with Ta was employed in fabricating multifilamentary composite wires of (NbTa)-Sn using the liquid-infiltration process. The superconducting A15 phase was formed with subsequent heat treatments at 800–950°C by the solid-liquid reaction. High inductive T c s of 18.2K with sharp transition width ( c s of ∼1.6 × 10 4 A/cm 2 at 20T and 4.2K were obtained. It was found that 2 wt.% Ta in the Nb was sufficient in the enhancement of the overall J c at the high fields and in increasing the H c2 (4.2K) to 25T.