Nuclear magnetic resonance study of vacancy and interstitial motion in scandium hydrides and deuterides
Nuclear Magnetic Resonance (NMR) methods have been used to study the nonstochiometric dihydrides and dideuterides of high purity scandium. For the first time, measurements have been made of the spin relaxation time T/sub 1/ and T/sub 2/ of all three nuclear species present (/sup 45/Sc, /sup 2/D, /sup 1/H) in a metal hydride (deuteride) system, permitting a comparison of the main features of both atomic and vacancy motion on the hydrogen sublattice. In the regions of the conventional diffusion induced /sup 45/Sc- and /sup 2/D-T/sub 1/ minima (<800 K), the relaxation rates are dominated by fluctuations of the quadrupolar interaction reflecting vacancy motion. The symmetric /sup 1/H-T/sub 1/ minimum can be well described by a Lorentzian (Debye) spectral density function. In contrast, the /sup 45/Sc-T/sub 1/ minimum shows for 1n(Sc-T/sub 1/) versus reciprocal temperature a substantially smaller slope on the high temperature side at high vacancy concentrations. (/sup 45/Sc-T/sub 1/) min saturates rapidly for vacancy concentrations larger than c/sub v/ > 0.03 and shows a weaker frequency dependence than expected. The jump-attempt frequencies ..nu../sub 0/ obtained from the /sup 45/Sc-T/sub 1/ data agree well with the values obtained from neutron scattering measurements, whereas the /sup 1/H-T/sub 1/ data yield anomalously low jump frequency prefactors. We interpret the departure of the /sup 45/Sc results from the Lorentzian model as indicating the formation of vacancy pairs and the importance of particle-particle interactions. The /sup 45/Sc- and /sup 2/D-T/sub 1/ data also reveal the importance of three particle correlations and conduction electron screening for the quadrupolar relaxation mechanism. At high temperatures (>800K), we have observed a new, previously unforeseen and essentially frequency independent decrease of T/sub 1/ and T/sub 2/ for all three nuclear species (/sup 45/Sc, /sup 2/D and /sup 1/H). This second, high temperature T/sub 1/ minimum suggests the formation of short-lived clusters on the H(D) sublattice.
- Research Organization:
- Ames Lab., IA (USA)
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 5317035
- Report Number(s):
- IS-T-1237; ON: DE86015767
- Resource Relation:
- Other Information: Thesis. Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
DEUTERIDES
INTERSTITIALS
NUCLEAR MAGNETIC RESONANCE
VACANCIES
SCANDIUM HYDRIDES
RELAXATION TIME
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DEUTERIUM COMPOUNDS
HYDRIDES
HYDROGEN COMPOUNDS
MAGNETIC RESONANCE
POINT DEFECTS
RESONANCE
SCANDIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
656000* - Condensed Matter Physics