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" An NMR investigation of metal hydrides "
Belhoul, Mourad
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Latin Dissertation
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| Record Number
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828475
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TLets348135
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| Main Entry
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Belhoul, Mourad
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| Title & Author
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An NMR investigation of metal hydrides\ Belhoul, Mourad
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| College
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University of Warwick
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| Date
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1983
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| student score
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1983
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| Degree
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Thesis (Ph.D.)
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| Abstract
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Pulsed nuclear magnetic resonance has been used for the investigation of YHx where x = 1.72, 1.81, 1.92 and 1.98, YD1.88, YH1.98 doped with 20, 50, 100, 200 and 915 ppm Gd, TiH1.74 doped with150, 500 and 104 ppm Mn and [Pd0.92y0.08]H0.51 • The Proton relaxation times T1 and T2 have been measured for'most of the samples at the resonance frequencies 7 and 45 MHz and for the range of temperature 120 K to about 1300 K. Measurements of the diffusion coefficient have also been performed at 7 MHz for YH1.98 and [Pd0. 92Y0.08]H0.51. T1 and T2 data for YHx show that the activation energy for hydrogen diffusion decreases by about a factor of two as the hydrogen concentration increases from x = 1.72 to x = 1.98. This is interpreted as due to the result of a large H-H repulsive interaction which increases with hydrogen concentration. The electronic contribution to T. clearly indicates that the d-density of states at the Fermi energy remains constant in the b-phase of yttrium hydride. The anomalous behaviour observed for both T1 and T2 at temperatures above 800 K is interpreted in terms of a highly correlated hydrogen motion at these temperatures. The behaviour of T1 for YD1.88 may be accounted for by some 20 ppm residual Gd impurity present in the sample. T1 data for YH1.98 doped with Gd show that an additional relaxation time arises from dipolar coupling between the proton nuclear spin and the local magnetic moment of the impurity. This process shows an effect on the observed T-j at concentrations of Gd as low as 2 ppm. The spin-lattice relaxation data for TiH1.74 doped with Mn reveal that the hydrogen diffusion is much faster in the vicinity of Mn than it is in the bulk and also shows that [Ti1-y, Mny ]Hx is a bottlenecked system. The activation energy deduced from the direct diffusion coefficient measurements in [Pdn,92Y0.08]H0.51 is consistent with a partially ordered sample. The much lower activation energy deduced from the T1 minimum indicates that the main contribution to T1 is due to paramagnetic impurity induced relaxation.
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QC Physics
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University of Warwick
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