Electron spin resonance studies of doped alumina and aluminium nitride

Abstract

In the first part of this thesis, Electron Paramagnetic Resonance (E.P.R.) techniques have been used to study the behaviour of gadohnium, chromium and iron in aluminium oxide single crystals and powders. E.P.R. single crystal spectra were recorded at room temperature for all three systems (with the dopant at various concentrations for the chromium case). The linewidth data extracted from these spectra of the single crystals showed good agreement with previously published results. The single crystal Spin-Hamiltonian parameters were used in computer simulations developed to predict the powder spectra for the chromium/aluminium oxide and iron/aluminium oxide systems and this allowed a comparison with the corresponding experimentally observed powder spectra due to Cr(^3+) and Fe(^3+ to) be made. The experimental linewidths have been interpreted in terms of dipolar and exhange broadening theories in order to show which mechanisms apply to different dopants. In all the three systems, the main effect is dipolar broadening and exchange interactions are very small at the dopant concentration levels examined. For both forms of specimen (i.e. single crystal or powder) the Kittel-Abrahams' theory gave the best agreement with experiment. The second part of the thesis was concerned with the elucidation of the structural and electrical nature of aluminium nitride using Electron Spin Resonance at room and low temperatures with related techniques including dielectric measurements. The results have been reported and discussed. It is shown that for the purer grade aluminium nitride both the permittivity and the dielectric loss are very nearly independent of frequency suggesting that the material behaves as a hopping conductor with electrical properties very similar to those of aluminium oxide, which is widely accepted as a useful substrate material in very large scale integration high performance packaging. In the less pure forms of aluminium nitride the major impurity was identified as iron whose presence was shown to be consistent with the higher values of permittivity observed. Finally, as part of a general survey of the dielectric behaviour of oxide and nitrogen ceramics, a comparison was drawn between the aluminium oxide-aluminium nitride ceramic systems.