J.L. Jorda

A New metallurgical investigation of the niobium-aluminium system

Abstract Previously published phase diagrams of the Nb-Al system are quantitatively contradictory in the niobium-rich region. To clarify the situation we applied new methods for the study of transformations and equilibrium phase fields at high temperatures. A revised accurate phase diagram is presented.

The physical and structural properties of superconducting A15-type Nb-Sn alloys

Bulk samples covering the entire homogeneity range of the Nb-Sn A15-phase were prepared by a new method: levitation melting under high argon pressure. The variations of the lattice parameter, superconducting transition temperature, resistivity and critical field slope were measured as a function of composition. A low-temperature X-ray diffraction study was undertaken in order to fix the compositional limit of the tetragonal phase. The theoretical expectations for the critical field slopes at the transition temperature, Tc, based on actually-observed alloy parameters, were found to be in good agreeement with measured values.

The phase diagram of the niobium-germanium system

Abstract The NbGe equilibrium phase diagram has been investigated by means of X-ray diffractometry, metallography, hardness measurements, microprobe analysis and differential thermal analysis up to 2200 °C. For temperatures higher than 1870 °C, the solidus lines were determined by thermal analysis on levitating samples. Particular attention was devoted to the homogeneity range of the superconducting A15 phase. We have found that the Ge-rich limit of this phase varies with temperature from 20 ± 1 at.% Ge at 1600 °C to 23 ± 1 at.% Ge at 1865 °C, the eutectic temperature. It is thus shown that the stoichiometric composition Nb 3 Ge is not reached in this system.

Phase relations and superconductivity in the binary Re-Si system

Abstract The phase diagram of the Re-Si system was reinvestigated by means of high temperature methods of analysis. We found several modifications to the existing diagram. An extended rhenium solid solution (up to 10 at.% Si) was established with a rapid quenching technique. Within this terminal solid solution, the superconducting transition temperature increased from 1.7 to 5.2 K. The phase corresponding to the “Re 5 Si 3 ” compound was homogeneous at 33 at.% Si. The peritectically formed equiatomic compound decomposed eutectoidally at 1650 °C and was superconducting at 1.5 K. The compound ReSi 2 was found to be off stoichiometric, occurring at the composition ReSi 1.8 .

On the formation and stability of the A15 phase in the Niobium-Gallium system

Abstract The Nb-rich portion of the Nb-Ga equilibrium phase diagram has been investigated up to 50 at.% Ga by means of X-ray diffractometry, metallography, hardness measurements and microprobe analysis. The direct observation of the phase relations at temperatures up to 2200 °C has been carried out independently by differential thermal analysis and a complementary technique, that of “simultaneous stepwise heating”. Particular attention was given to the high temperature part of the A15 phase. The Ga-rich limit of this phase was found to depend strongly on the temperature: it extends from 21 at.% Ga at 1000 °C to 25 at.% Ga at 1740 °C, the eutectic temperature.

Phase relations, thermochemistry and superconductivity in the ZrRh system

Abstract The phase relations in the ZrRh system were reinvestigated by differential thermal analysis, levitation thermal analysis, X-ray analysis electron microprobe analysis, microstructural examinations and measurements of the superconducting transition temperatures. A new complete phase diagram is presented. Owing to the occurrence of martensitic transformations; the central part of the diagram is particularly complicated. Observed enthalpies of formation are given for three intermediate compounds.

New ternary germanides RPd2Ge of the YPd2Si type

Abstract The crystal structures of the compounds RPd 2 Ge (R  all the lanthanides except Pm and Yb), YPd 2 Ge and YPd 2 Ga were found to be of the YPd 2 Si type (orthorhombic; space group, Pnma ; Z = 4). The YPd 2 Si type is an ordered derivative of the Fe 3 C type. Metallurgical, crystallographic and magnetic properties are reported and a comparison with the Heusler phases YPd 2 B (BIn, Sn, Pb and Bi) is made.

The V3Si phase: Type of formation and homogeneity range

Abstract Previously published phase diagrams of the V-Si system show either a peritectic or a congruent formation of the A15 phase V 3 Si. The present work, based on accurate high temperature investigations, establishes that the congruent formation is correct. A careful examination of the silicon-rich boundary of the A15 phase reveals a significant variation with temperature.

Superconductivity and phase relations in the Pd-Se system

Abstract The phase diagram of the Pd-Se system was reinvestigated between 0 and 40 at.% Se by differential thermal analysis, metallography and X-ray diffraction. The existence of the compounds Pd9Se2, Pd4Se, Pd7Se2, Pd34-Se11 and Pd7Se4 was confirmed. The alloys containing the Pd9Se2 phase have a characteristic lamellar structure which was investigated in detail by metallography, transmission electron microscopy and electron probe microanalysis. The compounds Pd9Se2, Pd7Se2 and Pd34Se11 are superconducting below 0.64, 0.53 and 2.66 K respectively. At the eutectic composition of 30 at.% Se, a superconducting amorphous phase with Tc = 2.04 K was obtained by liquid quenching. Almost temperature-independent small paramagnetic susceptibilities were found from 4.2 to 295 K for the superconducting compounds.

Phase relations in the vicinity of the compound YBa2Cu3O7 − δ at constant oxygen pressure

Abstract The phase relations in part of the BaOY2O3CuO system were investigated by differential thermal analysis coupled with thermographimetric measurements, X-ray and microprobe analysis, microstructural examinations in a light microscope and in a scanning electron microscope and inductive measurements of the superconducting transition temperatures. The superconducting compound YBa2Cu3O7 − δ shows no homogeneity range with respect to the metallic constituents. Solidus temperature for the pseudobinary BaCuO2CuO and formation temperatures for the compounds in the copper-rich part of the phase diagram are given.