Degree Type

Dissertation

Date of Award

1988

Degree Name

Doctor of Philosophy

Department

Physics and Astronomy

First Advisor

R. G. Barnes

Abstract

Pulsed nuclear magnetic resonance methods have been used to investigate the properties of various metal-hydrogen systems including ZrH[subscript] x, ScH[subscript] x, NbH[subscript] x, VH[subscript] x etc. For pure dihydride-phase samples of ZrH[subscript] x, the spin-lattice relaxation time T[subscript]1 has been measured as a function of temperature in the temperature range from 10 K to 1300 K at 12.2 MHz and 40 MHz. These measurements show that the activation energy E[subscript] a for hydrogen diffusion first increases smoothly from 0.57 eV/atom at x = 1.58 to 0.63 eV/atom at x = 1.93 and then increases quite rapidly near the stoichiometric limit, reaching 1.06 eV/atom at x = 1.98;T[subscript]1 measurements at temperatures below 300 K reveal that the d-band electronic states are split due to the Jahn-Teller effect. For ZrH[subscript] x samples doped with paramagnetic impurity ions (Mn, Cr, Fe), an additional spin-lattice relaxation rate R[subscript]1 p was observed. The rate R[subscript]1 p increases in the sequence Fe-Cr-Mn and also increases sharply with increasing hydrogen concentration in each case. The former result is consistent with the observation that the tendency towards localized-moment formation in Zr increases in the same sequence, whereas the latter may be accounted for by the anti-trapping behavior of these impurities;For dilute solid solution [alpha]-phase Sch[subscript] x, we measured T[subscript]1 of both [superscript]1H and [superscript]45Sc as a function of temperature to investigate hydrogen diffusion. The activation energy E[subscript] a = 0.54 eV/atom and attempt frequency [nu][subscript] o = 1. x 10[superscript]14 Hz were obtained. The absence of a prefactor anomaly in this dilute system is consistent with the hypothesis that such anomalies in other systems may result from repulsive particle-particle interactions at the saddle point;We have also observed anomalous behavior of the proton spin-lattice relaxation time T[subscript]1 at high temperatures (up to 1300 K) for hydrogen in faced-centered-cubic (fcc) dihydride phases of ZrH[subscript] x, TiH[subscript] x, YH[subscript] x and LaH[subscript] x and in the body-centered cubic (bcc) solid solution phases of NbH[subscript] x, VH[subscript] x and their alloys. In addition to the usual T[subscript]1 minimum, T[subscript]1 decreases sharply at higher temperatures, contrary to the expectation that T[subscript]1 would return to the value T[subscript]1 e determined by the conduction electron contribution to the total relaxation rate. This decrease in T[subscript]1 may have its origin in highly correlated hydrogen motion at high temperature. ftn*DOE Report IS-T-1359. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.

DOI

https://doi.org/10.31274/rtd-180813-11860

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Jinwoo Han

Language

en

Proquest ID

AAI8825917

File Format

application/pdf

File Size

142 pages

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