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Solid-State Proton Nuclear Magnetic Resonance Studies of Hydrogen Site Occupancies, Electronic Structure Properties, and Diffusion Behavior in Transition Metal Hydrides

Citation

Bowman, Robert Clark, Jr. (1983) Solid-State Proton Nuclear Magnetic Resonance Studies of Hydrogen Site Occupancies, Electronic Structure Properties, and Diffusion Behavior in Transition Metal Hydrides. Dissertation (Ph.D.), California Institute of Technology. https://resolver.caltech.edu/CaltechETD:etd-05152003-105639

Abstract

Solid-state NMR techniques have been used to measure the proton lineshapes, Knight shifts, and relaxation times in several transition metal hydrides. The objective of these studies is to obtain a better understanding of the roles of host metal structure and substitutional alloying on the hydrogen site occupancy, the electronic structure properties, and diffusion mechanisms.

An improved method for observing the rigid-lattice proton lineshapes and extracting the second moments has been developed. Comparisons of the experimental second moments for polycrystalline samples with the values calculated from Van Vleck formulas for nuclear dipolar interactions have indicated that only tetrahedral interstitial sites are occupied by the protons in TiHx, ZrHx, crystalline TiCuH0.94, Ti2CuH1.9, and Zr2PdHx (with x < 2) while both tetrahedral and octahedral sites can be occupied in amorphous a-TiCuH1.4, Ti2CuH2.6, and Zr2PdHx (x > 2).

The proton Knight shifts and low-temperature spin-lattice relaxation times have been related to the local densities of electron states at the Fermi levels N(EF) in Ti1-yVyHx, TiCr1.8Hx, TiCr1.9Hx, TiCuHx, Ti2CuHx, ZrHx, and Zr2PdHx. The dominant conduction electron hyperfine interaction for protons is a transferred "core-polarization" of the paired hydrogen 1s electrons through spin exchange with the unpaired metal d electrons. The proton NMR parameters have confirmed that decreases in N(EF) through a Jahn-Teller type mechanism are associated with the temperature and composition dependent tetragonal distortions in Ti1-yVyH1.95 and ZrHx (where 1.75 ≤ x ≤ 2.0). The proton NMR results are consistent with recent band theory calculations and photoemission spectra. Unusual N(EF) increases with hydrogen content, which are supported by independent magnetic susceptibility data, have been observed in TiCr1.8Hx, TiCr1.9Hx, and Ti2CuHx. The proton parameters suggest that significant differences in N(EF) for the crystalline and amorphous phases of TiCuHx and Zr2PdHx may reflect a smearing of energy levels in the disordered phases.

The proton rotating-frame relaxation times for Ti1-yCuyHx indicate both crystal structure and hydrogen site occupancies greatly influence diffusion behavior. A significant enhancement in hydrogen mobility for amorphous a-TiCuH1.4 has been confirmed; but, short range order is probably retained in the structure of a-TiCuH1.4. Reductions in activation energies are observed when octahedral sites exist in the diffusion paths between tetrahedral sites.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Chemistry
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Goddard, William A., III
Thesis Committee:
  • Goddard, William A., III (chair)
  • Chan, Sunney I.
  • Bercaw, John E.
  • Johnson, William Lewis
  • Rhim, Won-Kyu
Defense Date:30 August 1982
Additional Information:Thesis file (PDF) missing pp. 177.
Funders:
Funding AgencyGrant Number
CaltechUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Record Number:CaltechETD:etd-05152003-105639
Persistent URL:https://resolver.caltech.edu/CaltechETD:etd-05152003-105639
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/0022-2364(82)90299-2DOIArticle adapted for Chapter 3.
https://doi.org/10.1103/PhysRevB.26.2652DOIArticle adapted for Chapter 4.
https://doi.org/10.1103/PhysRevB.24.2232DOIArticle adapted for Chapter 5.
https://doi.org/10.1103/PhysRevB.27.1474DOIArticle adapted for Chapter 6.
https://doi.org/10.1016/0167-577X(82)90024-6DOIArticle adapted for Chapter 7.
https://doi.org/10.1103/PhysRevB.26.6362DOIArticle adapted for Chapter 8.
ORCID:
AuthorORCID
Bowman, Robert Clark, Jr.0000-0002-2114-1713
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1809
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:15 May 2003
Last Modified:02 Dec 2020 01:22

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