Neutron Scattering Studies of Fluorite Compounds.
Abstract
Available from UMI in association with The British Library. Requires signed TDF. The properties of some important compounds with the fluorite structure have been investigated using neutron scattering techniques. All of the compounds in this study have important technological applications, as well as being of intrinsic scientific interest. Inelastic neutron scattering and high temperature technology have been used to measure phonon energies in thorium dioxide at temperatures above 3000K. These phonon energies have been used to determine the elastic constants as a function of temperature. Thorium dioxide provides an interesting comparison with uranium dioxide which has been studied in order to try and establish the cause of the anomalously large enthalpy of this compound. Quasielastic neutron scattering has been used to demonstrate that the dynamic ionic-disorder which occurs in ThO_2 behaves in a similar way to that observed in UO _2 at high temperature. Whilst at only 12K, splittings have been measured in the crystal field excitations of UO_2 which have a significant effect on the theoretical analysis of its thermodynamic properties. This experiment was performed using neutrons scattered with a high energy transfer. Elastic and quasielastic diffuse scattering have both been used to investigate the vacancy-stabilised cubic structure of yttria doped zirconia. Computer modelling of the measured neutron scattering intensities has played a vital role in this part of the study. By the combination of neutron scattering measurements and computational techniques a three part model has been developed for the defect structure in yttria-stabilised zirconia which can explain the ionic conductivity in this compound. Ionic disorder has been observed in the anti-fluorite compounds lithium oxide and magnesium silicide at high temperature, using diffuse quasielastic neutron scattering. The full phonon energy dispersion relation and the elastic constants at high temperature have also been determined in magnesium silicide from inelastic neutron scattering measurements.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1987
- Bibcode:
- 1987PhDT.......172H
- Keywords:
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- Physics: Elementary Particles and High Energy