Jean-Louis Soubeyroux

Etude par diffraction de neutrons de la solution solide Pb1−xBixF2+x: Correlations entre structure et conductivité ionique

Bragg neutron diffraction studies have been carried out on the fluorite-type solid solutions Pb 1− x Bi x F 2+ x (0≤ x ≤0.50). The distribution of fluorine atoms between normal and interstitial sites as a function of the substitution rate is determined. Electrical and structural data are correlated. These results are compared with those obtained from the Ca 1− x Y x F 2+ x solution.

Structural study of the hydrides NiTiHx (X = 1.0 and 1.4)

Abstract The hydrides NiTiH x ( x = 1.0 and 1.4) have been prepared by a two-step method comprising an electrochemical treatment followed by a hydrogen gas pressure charging. The hydrides so obtained have a crystal structure of tetragonal symmetry and the hydrogen location has been determined by powder neutron diffraction. Hydrogen atoms occupy two octahedral sites. The hydrides do not present any structural phase transition as a function of temperature, in contrast to the parent alloy NiTi. The crystal structure is compared with other filled alloys of CsCl-type structure.

Magnetoelastic transition and antiferro-ferromagnetic ordering in the system MnFeP1-yAsy

Abstract Neutron diffraction experiments have been performed on a range of hexagonal structures in the MnFeP 1− y As y system which exhibit a magnetoelastic transformation. Local transformations accompanying both the hexagonal crystal structure and the magnetic ordering have been measured. The anisotropic changes observed in the unit cell parameters arise primarily from the expansion of the shortest Fe-Fe distance when the compounds transform from the antiferro- to the ferromagnetic state. Substitution of As for P favours such as a transition via the preferential expansion of selected basal interatomic bond lengths. The incommensurate type of antiferromagnetic ordering indicates some competing interatomic exchange interactions. The net result of these phenomena is that the magnetic moment of iron increases markedly and adopts a more localized weak ferromagnetic state.

Neutron powder diffraction study of the desorption of deuterium in Nd2Fe17Dx≈5

Abstract We report on the location of interstitial deuterium in Nd2Fe17 and on the desorption process. The hydrogen atoms fill both octahedral and tetrahedral sites. Powder neutron diffraction experiments have permitted us to point out a difference in stability between the interstitial sites. The role of each site on the structural and magnetic properties is discussed.

Thermal treatments for biaxially textured Cu-Ni alloys for YBCO coated conductors

We have studied the thermal treatments necessary to texture Cu-Ni alloys in view of applications as substrate for the YBCO coated conductors. Several alloy compositions chosen in order to avoid magnetism of the tapes have been elaborated by the rolling (RABiTS) method. Analyzes of the texture as a function of annealing temperature have been done by X-ray and neutron diffractions, pole figures by EBSD and X-rays. The results show that the annealing temperature is dependant of the alloy composition and must be determined precisely for each composition. Good biaxial textures have been obtained on these cheap alloys.

Phase stability and neutron diffraction studies of Laves phases Zr(Cr1−xMx)2 with M = (Cu0.5Ni0.5) and 0 < x < 0.2 and their hydrides

Abstract Laves phases of composition Zr(Cr 1− x M x ) 2 with M = (Cu 0.5 Ni 0.5 ) and 0 ⩽ x ⩽ 0.2 have been synthesised with the hexagonal C14- and/or cubic C15-type structures. By X-ray and neutron diffraction we have determined the structures of the alloys, and in particular the sites for the 3d metal substitution. The position of the hydrogen atoms in the structures and the occupation of the different sites of the hydrides have been determined. Purity and quality of polycrystalline alloys have been checked by using scanning electron microscopy and energy dispersive X-ray analysis techniques. The effects of the M/Cr substitution have been studied for phase stability, maximum hydrogen content and hydrogen site stability and analyzed in view of applications as electrodes in H M batteries.

Role of the (H,C,N) interstitial elements on the magnetic properties of iron-rare earth permanent magnet alloys

Abstract A comparison is made between the intermetallic compounds R2Fe14B, R2Fe17 and RFe12−xMx (R = rare earth metal and M = Ti, Mo) and their interstitial derivatives (hydrides, carbides and nitrides). The role of the different interstitial elements on the magnetic properties will be reviewed through their crystal structure (in particular the localization of the interstitial) and through experimental work done by magnetic susceptibility, Curie point measurements and neutron diffraction.

Advances on fluorine ion conductors, basic and applied research

Abstract Fluorides which are insulators, often possess a high anionic conductivity due to weak chemical bonding of the F - ion. The examination of the known ionic conductors allows us to point out some general criteria characteristic of high mobility of F - . The mechanisms of conduction determined on the basis of neutron diffraction are described. The possibility of utilization of such materials for thermodynamic measurements, specific electrodes, solid state batteries, electrochromic devices and gas sensors are examined.

Nitrogen gas pressure synthesis and neutron diffraction study of R2Fe17N3 with RCe and Nd

Abstract A variant synthesis route has been developed using high pressure nitrogen gas, leading to a lower reaction temperature and time and a higher nitrogen content. Here we report on a structural and magnetic study of Ce 2 Fe 17 ,N 3 and Nd 2 Fe 17 N 3 synthesized by this method. The compounds have been investigated by means of neutron powder diffraction at 2 and 300 K. The impact of nitrogen insertion on the iron and rare earth magnetic moments is discussed. Finally, enlightening comparisons are made with some iron nitrides (Fe 4 N and Fe 16 N 2 ). The refined site-dependent iron magnetic moments appear to vary significantly with the interatomic distances between iron and nitrogen.

Physical properties of bulk amorphous glasses: influence of physical aging and onset of crystallisation

Measurements of the dynamic shear modulus and of the internal friction are performed in a bulk amorphous Zr57–Ti5–Cu20–Ni8–Al10 (at.%) alloy, both during heating and cooling with different cooling rates and different frequencies. The kinetic aspect of the glass transition is demonstrated. The onset of the crystallisation process induces a modulus increase and an internal friction decrease, due to the decrease of the atomic mobility resulting from the crystallisation process. Experimental results are well described using a physical model of the mechanical response of the amorphous material and especially of the characteristic times of the atomic mobility.