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Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Douglas S. McGregor / Strengthening the crystal lattice of lanthanide halides, which are brittle, anisotropic, ionic crystals may increase the availability and ruggedness of these scintillators for room-temperature γ-ray spectroscopy applications. Eight dopants for CeBr[subscript]3, including CaBr[subscript]2, SrBr[subscript]2, BaBr[subscript]2, ZrBr[subscript]4, HfBr[subscript]4, ZnBr[subscript]2, CdBr[subscript]2, and PbBr[subscript]2, were explored at two different doping levels, 500ppm and 1000ppm, in an effort to identify potential aliovalent strengthening agents which do not adversely affect scintillation performance. All dopants and doping levels exhibited improved ingot yields over the undoped case, indicating an improvement in the ease of crystal growth. Scintillation performance was gauged using four key metrics. Scintillation emission spectra or, rather, radioluminescence spectra were recorded using x-ray irradiation. Total light yield was estimated through pulse height comparison with bismuth germanate (BGO) scintillators. Scintillation kinetics were checked by measuring single interaction pulses directly output by a fast response PMT. Finally, light yield proportionality was measured using a Compton coincidence system. Samples from each ingot were harvested to benchmark their performance with the four metrics. Of the eight dopants explored, only BaBr[subscript]2 and PbBr[subscript]2 clearly altered scintillation spectral emission characteristics significantly. The remaining dopants, CaBr[subscript]2, SrBr[subscript]2, ZrBr[subscript]4, HfBr[subscript]4, CdBr[subscript]2 and ZnBr[subscript]2, altered scintillation performance to a lesser degree. No dopant appeared to affect light yield proportionality, nor did any drastically alter the light decay characteristics of CeBr[subscript]3. HfBr[subscript]4 and ZnBr[subscript]2-doped CeBr[subscript]3 exhibited the highest light yields, significantly higher than the undoped CeBr[subscript]3 samples tested. Finally, aliovalent doping appeared to greatly improve CeBr[subscript]3 ingot yields, regardless of the dopant, thus it is a promising method for improving crystal strength while not deleteriously affecting scintillation performance. HfBr[subscript]4 and ZnBr[subscript]2 both demonstrated high performance without any noticeable negative side-effects and are prime candidates for future study.

Polymer electrolytes are widely used as ion transport media in vital applications such as energy storage devices and electrochemical displays. To further develop these materials, it is important to understand their ionic conductivity mechanisms. It has long been thought that ionic conduction in a polymer electrolyte occurs in the amorphous phase, while the crystalline phase is insulating. However, this picture has recently been challenged by the discovery of the crystalline system LiXF6∙PEO6 (X=P, As or Sb) which exhibits higher conductivity than its amorphous counterpart. Their structures comprise interlocking hemi-helical PEO-chain pairs containing Li+ ions and separating them from the XF6- anions. The first Molecular Dynamics (MD) simulation study of the LiPF6∙PEO6 system is presented in this thesis. Although its conductivity is too low for most applications at ambient temperature, it can be enhanced by iso- and aliovalent anion doping. It is shown that the diffraction-determined structure is well reproduced on simulating the system using an infinite PEO-chain model. The Li-Oet coordination number here becomes 6 instead of 5; minor changes also occur in the polymer backbone configuration. The crystallographic asymmetric unit and diffraction profiles are also reproduced. On simulating a shorter-chain system (n=22), more resembling the real material, the structure retains its double hemi-helices, but the polymer adopts a more relaxed conformation, facilitating the formation of Li+-PF6- pairs. Infinite-chain simulation shows the ionic conduction to be dominated by anion motion, in contrast to earlier NMR results. The effects of doping are also reproduced. Shortening the polymer chain-length has the effect of raising the transport number for lithium, thereby bring it into better agreement with experiment. It can be concluded that it is critical to take polymer chain-length and chain-termination into account when modelling ionic conductivity mechanisms in crystalline polymer electrolytes.