Studies on the reactivity of coinage metals and rare earth metals in alkali metal/polytelluride fluxes

Over the past decade, the polychalcogenide flux method has become an established technique for discovering new solid state compounds. The advantage to using molten fluxes is that they allow the reaction system to choose its own route (either kinetic or thermodynamic) without forcing it to a certain stoichiometry or structure type. The materials discovered by this method can be used for a wide variety of applications, including batteries, lasers, non-linear optics, photovoltaics, composites, and thermoelectrics. In order to maximize the probability that the compounds formed will possess new structure types, a quaternary system was explored in which two metals with very different coordination preferences, namely a coinage metal and a rare earth metal, were reacted in an alkali metal/polychalcogenide flux. Explorations in this system with sulfur and selenium proved to be successful, and so we decided to expand this chemistry into the polytelluride system. As a result, several new compounds were discovered and most notably, the structure types formed were very different than those previously found in the sulfur and selenium systems. Many of the compounds contain stacking layers that can be described as a square Te net. These Te nets have a propensity to distort, which gives rise to subtle crystallographic superstructures.; In this dissertation, the synthesis, structure, and physicochemical properties of many new phases will be reported. In systems where only a rare earth metal reacted in a molten A₂Te_x flux, the family of compounds ALn₃Te₈ was discovered whose members include CsCe ₃Te₈, RbCe₃Te₈, KCe₃Te ₈, and KNd₃Te₈. Several quaternary phases of the type A_wM_xLn_yTe_z were also discovered by reacting both a coinage metal and a rare earth metal in a molten A ₂Te_x flux, including CsCuUTe₃, RbCuUTe₃, KCuUTe₃, KCuCeTe₄, RbCuCeTe₄, Na_0.8 Ag_1.2CeTe₄, K_2.5Ag_4.5Ce ₂Te₉, K_2.5Ag_4.5La₂Te ₉, K₂Ag₃CeTe₄, Rb₂Cu ₃CeTe₅, KCu₂EuTe₄, Na_0.2Ag _2.8EuTe₄, and K_0.65Ag₂Eu_1.35Te ₄. In the case where a flux was not used, the ternary phase Cu _xUTe₃ (x = 0.25 and 0.33) was discovered. Finally, the cage compounds A₂MCu₈Te₁₀ (K₂BaCu ₈Te₁₀, Rb₂BaCu₈Te₁₀, Cs ₂BaCu₈Te₁₀, and Rb₂EuCu₈Te ₁₀) were investigated for their promising thermoelectric properties.