Deuterium site occupancy and phase boundaries in ZrNiDx(0.87x3.0)

R. C. Bowman, Jr., Natalie L. Adolphi, Son-Jong Hwang, J. G. Kulleck, T. J. Udovic, Q. Huang, and H. Wu
Phys. Rev. B 74, 184109 – Published 8 November 2006

Abstract

ZrNiDx samples with compositions between x=0.87 and x=3.0 were investigated by H2 magic-angle spinning nuclear magnetic resonance spectroscopy (MAS-NMR), powder x-ray diffraction (XRD), neutron vibrational spectroscopy (NVS), and neutron powder diffraction (NPD). The rigid-lattice MAS-NMR spectrum for a ZrNiD0.88 sample in the triclinic β phase shows a single phase with two well-resolved resonances at +11.5 and 1.7ppm, indicating that two inequivalent D sites are occupied, as was observed previously in ZrNiD1.0. For ZrNiD0.88, the ratio of spectral intensities of the two lines is 1:0.76, indicating that the D site corresponding to the +11.5ppm line has the lower site energy and is fully occupied. Similarly, the neutron vibrational spectra for ZrNiD0.88 clearly confirm that at least two sites are occupied. For ZrNiD1.0, XRD indicates that 5% of the metal atoms are in the γ phase, corresponding to an upper composition for the β phase of x=0.90±0.04, consistent with the MAS-NMR and neutron vibrational spectra indicating that x=0.88 is single phase. The MAS-NMR and NVS of ZrNiD1.87 indicate a mixed-phase sample (β+γ) and clearly show that the two inequivalent sites observed at x=0.88 cannot be attributed to the sites normally occupied in the γ phase. For ZrNiD2.75, NPD results indicate a γ-phase boundary of x=2.86±0.03 at 300K, increasing to 2.93±0.02 at 180K and below, in general agreement with the phase boundary estimated from the NVS and MAS-NMR spectra of ZrNiD1.87. Rigid-lattice H2 MAS-NMR spectra of ZrNiD2.75 and ZrNiD2.99 show a ratio of spectral intensities of 1.8±0.1:1 and 2.1±0.1:1 (Zr3Ni:Zr3Ni2), respectively, indicating complete occupancy of the lower-energy Zr3Ni2 site, consistent with the NPD results. For each composition, the correlation time for deuterium hopping was determined at the temperature where resolved peaks in the MAS-NMR spectrum coalesce due to motion between inequivalent D sites. The measured correlation times are consistent with previously determined motional parameters for ZrNiHx.

    • Received 7 June 2006

    DOI:https://doi.org/10.1103/PhysRevB.74.184109

    ©2006 American Physical Society

    Authors & Affiliations

    R. C. Bowman, Jr.1,*, Natalie L. Adolphi2, Son-Jong Hwang3, J. G. Kulleck1, T. J. Udovic4, Q. Huang4, and H. Wu4,5

    • 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA
    • 2New Mexico Resonance, Albuquerque, New Mexico 87106, USA
    • 3The Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
    • 4NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8562, USA
    • 5Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742-2115, USA

    • *Please correspond with Robert Bowman at JPL Mail Stop 79-24. FAX: 1-818-393-4878. Electronic address: robert.c.bowman-jr@jpl.nasa.gov

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    Issue

    Vol. 74, Iss. 18 — 1 November 2006

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