ABSTRACT
YMn2 forms either interstitial YMn2Hx hydrides for x < or = 4.5 or a complex YMn2H6 hydride when submitted to high hydrogen pressure. These compounds have been studied by inelastic neutron scattering (INS) in order to clarify the different modes of H vibration. The INS spectra of YMn2Hx hydrides are strongly dependent on the H content. YMn2H6 and YMn2D6 show broad bands, also observed by Raman and IR spectroscopy, assigned to H-Mn-H (or D) and Mn-H bending and stretching modes. Both ErMn2D6 and ErMn1.8Fe0.2D6 show, in addition to the H vibration mode, an intense band at 215 cm(-1) which has been attributed to a magnetic excitation of Er3+ in view of its momentum transfer dependence.
ABSTRACT
The exposure of (Ti(1-x)Zr(x))Co(2.00) intermetallic alloys to hydrogen at high pressure caused (Ti(1-x)Zr(x))Co(2.00) (x = 0.50-0.90) hydrides in the alloy. The crystalline structural, electronic, and magnetic properties of parent alloys and of their hydrides were determined by using XRD (X-ray powder diffraction) and XAS (X-ray absorption spectrometry) and by the use of SQUID (a superconducting quantum interference device). Hydrogenation did not alter the crystal structure of the parent alloy, but it did increase the volume of the unit cell. An in situ Co K-edge XAS study of the hydride revealed that the valence state of Co increased during discharge (which is the release of hydrogen from the hydride). Hydrogenation of the parent alloy also reduced the magnetic moment. A possible mechanism of discharge for the hydride is also proposed.
ABSTRACT
DyMn(2)D(6) has been prepared by applying high gaseous deuterium pressure on DyMn(2). This phase is isostructural with other RMn(2)D(6) (R = Y, Er) compounds and crystallizes with a K(2)PtCl(6) type structure having an ordered anion and a partially disordered cation arrangement because Dy and half the Mn atoms are randomly substituted in the same 8c site. The reverse susceptibility follows a Curie-Weiss law with an effective moment of 10 µ(B) similar to that of DyMn(2). Short range magnetic order, corresponding to ferromagnetic correlations, is observed in the neutron patterns up to 10 K and can be attributed to Dy-Dy interactions. The decomposition of the deuteride into Mn and DyD(2), studied by thermal gravimetric analysis, occurs between 470 and 650 K. A further deuterium desorption takes place above 920 K.
