Synthesis and Characterization of Bulk and Thin Film Clathrates for Solid State Power Conversion Applications

Thin films of the type I clathrate Ba₈Ga₁₆Ge ₃₀ have been synthesized by the pulsed laser ablation technique. The relatively low ablation threshold of this material at the UV wavelength leads to the ejection of particulates during laser-target interaction. The optimum laser fluence for the formation of stoichiometric films with the lowest particle density was 2.5 J/cm² . Excitation of the UV laser generated plasma by a second pulsed CO₂ laser further reduced particulate ejection and produced broader expansion profiles leading to large area uniform films. Films deposited by this method on quartz substrates were polycrystalline and showed semiconducting behavior. High purity type II Na_xSi₁₃₆ clathrates in bulk form have been synthesized by solid state reactions. The electrical properties of Na _xSi₁₃₆ (0 < x < 24) clathrates show a clear dependence on Na content, with resistivities that span several orders of magnitude