Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Ionic conductivity measurements have been made on pure and strontium- and sulphide-doped sodium chloride and the data analysed by means of a non-linear least squares fitting routine. The purpose of this investigation was two-fold. First, the question as to what types of defects occur in NaCl needed to be resolved. Recent work on KCl indicated that a small concentration of Frenkel defects was present on both sub-lattices in addition to Schottky defects, which have been assumed to predominate in alkali halides. Secondly, a wide variety of values for the anion vacancy migration energy have been given in the literature and it was hoped that the present investigation would help to resolve the correct value of this defect energy. The analysis of the data indicated that Schottky defects do indeed predominate in NaCl. A value of 0.744 eV was determined for the anion migration enthalpy.;In addition to this, calculations were carried out with new potentials for SrCl{dollar}\sb2{dollar} and Na{dollar}\sb2{dollar}S using the HADES code. The main purpose of these calculations was to develop potentials to be used in defect calculations of NaCl containing Sr{dollar}\sp{lcub}2+{rcub}{dollar} and S{dollar}\sp{lcub}2-{rcub}{dollar} impurities; however the availability of these potentials made it possible to carry out additional calculations on SrCl{dollar}\sb2{dollar} and Na{dollar}\sb2{dollar}S. Although the problem of low defect migration energies commonly found in defect calculations of fluorites still persisted, some improvements were made with SrCl{dollar}\sb2{dollar}. No defect calculations on Na{dollar}\sb2{dollar}S had been done previously.;An investigation of the quasi-harmonic approximation was carried out with a set of temperature dependent potentials for NaCl, KCl, and KBr. In the past, quasi-harmonic calculations have been undertaken only with potentials developed at 0 K. However, a lattice which is strain-free at 0 K is no longer at equilibrium at higher temperatures. The temperature dependent potentials were developed over a wide temperature range by fitting to the physical properties of the crystal at 50 K intervals and minimizing the bulk lattice strain. The resulting defect energies were compared to values calculated using the potentials of Catlow, Diller, and Norgett developed at 0 K, and additional thermodynamic properties were calculated in the quasi-harmonic approximation.



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