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Deuterium site occupancy and phase boundaries in ZrNiDx (0.87<=x<=3.0)

Bowman, R. C., Jr. and Adolphi, Natalie L. and Hwang, Son-Jong and Kulleck, J. G. and Udovic, T. J. and Huang, Q. and Wu, H. (2006) Deuterium site occupancy and phase boundaries in ZrNiDx (0.87<=x<=3.0). Physical Review B, 74 (18). Art. No. 184109. ISSN 1098-0121. doi:10.1103/PhysRevB.74.184109.

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ZrNiDx samples with compositions between x=0.87 and x=3.0 were investigated by 2H 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 beta phase shows a single phase with two well-resolved resonances at +11.5 and −1.7 ppm, 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 +11.5 ppm 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 gamma phase, corresponding to an upper composition for the beta 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 (beta+gamma) and clearly show that the two inequivalent sites observed at x=0.88 cannot be attributed to the sites normally occupied in the gamma phase. For ZrNiD2.75, NPD results indicate a gamma-phase boundary of x=2.86±0.03 at 300 K, increasing to 2.93±0.02 at 180 K and below, in general agreement with the phase boundary estimated from the NVS and MAS-NMR spectra of ZrNiD1.87. Rigid-lattice 2H 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.

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Bowman, R. C., Jr.0000-0002-2114-1713
Hwang, Son-Jong0000-0002-3210-466X
Additional Information:© 2006 The American Physical Society (Received 7 June 2006; revised 18 August 2006; published 8 November 2006) The authors appreciate helpful conversations with M.S. Conradi and also the assistance of M. Prina with the preparation of some of the ZrNi(H/D)x samples at JPL. N.L.A. gratefully acknowledges support from Research Corporation (Grant No. CC4705) and the NSF (Grant No. DMR-9804094). This research was partially performed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautical and Space Administration. The NMR facility at Caltech was supported by the National Science Foundation under Grant No. 9724240 and partially supported by the MRSEC Program of the National Science Foundation under Grant No. DMR-0080065.
Funding AgencyGrant Number
Research Corp.CC4705
Subject Keywords:zirconium compounds; nickel compounds; magic angle spinning; X-ray diffraction; vibrational states; neutron diffraction; phase diagrams; spectral line intensity
Issue or Number:18
Record Number:CaltechAUTHORS:BOWprb06
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:6391
Deposited By: Archive Administrator
Deposited On:06 Dec 2006
Last Modified:08 Nov 2021 20:33

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