Fundamental investigations of skutterudite phase formation by the modulated elemental reactant method

The traditional methods of solid-state inorganic synthesis, whether by the high temperature annealing of finely ground reactants or the preparation of a fluid or flux containing the reactants, provide very little information about the mechanism of the reaction itself. In the case of annealed reactant powders there are often multiple phases which nucleate in the reaction process, and differential diffusion rates of reactants through the crystalline phases formed at the interfaces presents a very complicated system from which it is nearly impossible to determine the mechanism of the reaction. For reactions performed in a fluid phase, the reaction process is complicated by the components of the fluid itself, which may impact the reaction mechanism. The ideal synthesis system for examining solid-state reaction mechanisms is to nucleate single pure phases from intimately mixed (or homogeneous) reactants. The Modulated Elemental Reactant method pioneered by the Johnson Lab provides just such an opportunity. This dissertation contains studies directed at understanding the interrelationship of composition, nucleation and diffusion using this synthesis method in several solid-state reactions.;The composition dependence of the nucleation energy of a metastable binary crystalline phase nucleating from a homogenous mixture of reactants has been measured and is presented here. Additionally, a study of the composition dependence of the nucleation energy of a similar ternary phase is also presented to examine the effect of the addition of the ternary species on the nucleation behavior of the phase.;The successful synthesis of a new metastable binary phase with the skutterudite crystal structure, NiSb3, is also shown. The existence of this phase was hypothesized after careful comparison of the Co-Sb and Ni-Sb phase diagrams showed a general similarity in the shape of the diagram above ∼50% Sb with the exception of a skutterudite phase present only in the Co-Sb system. The ability to use phase diagram comparison to predict the existence of new metastable phases, and then to successfully prepare them, is a potentially very powerful technique in solid-state synthesis.;The preparation of new inorganic multilayers composed of alternating layers of different crystalline phases (including some metastable phases) is also presented here as a study of the potential for using this synthesis method to produce these types of structures using phases with no preferred orientation.;This dissertation includes my previously published co-authored materials.