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An NMR investigation of metal hydrides / Mourad Belhoul

Public ISBD Titre : An NMR investigation of metal hydrides Type de document : texte imprimé Auteurs : Mourad Belhoul, Auteur ; G. A. Styles, Directeur de thèse Editeur : Midlands : University of Warwick Année de publication : 1983 Importance : 253 f. Présentation : ill. Format : 30 cm. Note générale : Thèse de Doctorat : Physiques : Midlands, University of Warwick : 1983 Bibliogr. [17] f. Annexe f. 254 - 272 Langues : Anglais (eng) Mots-clés : Nuclear  magnetic  resonance Hydrogen  diffusion Spin-lattice  relaxation Index. décimale : D003583 Résumé : Pulsed nuclear magnetic resonance has been used for the investigation of YHx where x = 1.72, 1.81, 1.92 and 1.98, YD₁̣₈₈, YH₁̣₉₈ doped with 20, 50, 100, 200 and 915 ppm Gd, TiH₁̣₇₄ doped with 150, 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 YH₁̣₉₈ 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 T₁ clearly indicates that the d-density of states at the Fermi energy remains constant in the β-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 YD₁̣₈₈ may be accounted for by some 20 ppm residual Gd impurity present in the sample. T₁ data for YH₁̣₉₈ 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 T₁ at concentrations of Gd as low as 2 ppm. The spin-lattice relaxation data for TiH₁̣.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 [Pd₀.₉₂Y₀.₀₈]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. An NMR investigation of metal hydrides [texte imprimé] / Mourad Belhoul, Auteur ; G. A. Styles, Directeur de thèse . - Midlands : University of Warwick, 1983 . - 253 f. : ill. ; 30 cm. Thèse de Doctorat : Physiques : Midlands, University of Warwick : 1983 Bibliogr. [17] f. Annexe f. 254 - 272 Langues : Anglais (eng) Mots-clés : Nuclear  magnetic  resonance Hydrogen  diffusion Spin-lattice  relaxation Index. décimale : D003583 Résumé : Pulsed nuclear magnetic resonance has been used for the investigation of YHx where x = 1.72, 1.81, 1.92 and 1.98, YD₁̣₈₈, YH₁̣₉₈ doped with 20, 50, 100, 200 and 915 ppm Gd, TiH₁̣₇₄ doped with 150, 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 YH₁̣₉₈ 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 T₁ clearly indicates that the d-density of states at the Fermi energy remains constant in the β-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 YD₁̣₈₈ may be accounted for by some 20 ppm residual Gd impurity present in the sample. T₁ data for YH₁̣₉₈ 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 T₁ at concentrations of Gd as low as 2 ppm. The spin-lattice relaxation data for TiH₁̣.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 [Pd₀.₉₂Y₀.₀₈]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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Code-barres	Cote	Support	Localisation	Section	Disponibilité	Spécialité	Etat_Exemplaire
D003583	D003583	Papier	Bibliothèque centrale	Thèse de Doctorat	Disponible