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Title: Nuclear spin relaxation in conducting liquids
Author: Moore, David Shaw
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1972
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Measurements have been made of the motions of atoms and conduction electrons in a number of liquid metallic and liquid semiconducting elements and alloys as a function of composition and temperature using the method of nuclear magnetic resonance (NMR). A description of a coherent NMR pulse spectrometer constructed in the course of the work is given. Nuclear spin-lattice relaxation r2.te measurements have been made for 27Al in Al-Si, 115 In in Bi-In and In-Sb, l21Sb in Bi-Sb and In-Sb, and 209 Bi in Bi-In, Bi-Pb, Bi-Sb and Bi-Sn. Where resonance shifts wore not already available in the literature these have also been measured (with the exception of that of 27A1). These relaxation rates are compared to those calculated from the resonance shifts using the Korringa relationship. An additional relaxation rate appears showing a broad maximum in the middle of the composition range for all the nuclei observed except 27 AI, being as much as eight times as large as the extra rate in the pure metal. This is identified as arising from the fluctuations of the electric field gradients due to the ionic motions interacting with the quadrupole moment of the nucleus. This has led to an extension by Sholl of his theory of electric quadrupolar relaxation in pure liquid metals to the case of liquid alloys to explain these results. The theoretical expression contains two integral terms; the first arising from the two body correlation function, the second arising from the three body correlation function. To fit the theoretical expression to the experimental data it is shown to be necessary to set the second term near to the magnitude of the first but opposite in sign, and then good agreement can be obtained. In order to discuss the data in terms of this theory three simplifying assumption') must be made. It is shown that the assumptions concerning radial distribution functions and self-diffusion coefficients are reasonable, whereas that concerning the representation of the electric field gradient may not be. Nuclear resonance shifts and spin-lattice relaxation rates t:or 125Te in liquid Te-Tl alloys have been measured in the range Te 100 to Tl 70. At 750 K the shift, measured with respect to solid tellurium decreases from + 0.38% to - 0.08% across the composition range whereas the relaxation rate remains approximately constant at 5 x l10³s over most of the range. Correlation of the temperature dependences of the total magnetic suceptibility and the shift shows that the changes in shift are principally clue to changes in density of states at the Fermi level rather than in the electronic wavefunction at tellurium nuclei. In the region near TeTl 2 where the density of states is low the relaxation rate is considerably shorter than that predicted from the Korringa relationship and the observed shift. This is interpreted as due to partial localisation of the conduction electrons.
Supervisor: Not available Sponsor: Science Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics