Structure and transport properties of dense polycrystalline Clathrate-ii (k, ba)16(ga, sn)136 synthesized by a new approach employing SPS

Abstract

Tin clathrate-II framework-substituted compositions are of current interest as potentialthermoelectric materials for medium-temperature applications. A review of the literature revealsdifferent compositions reported with varying physical properties, which depend strongly on theexact composition as well as the processing conditions. We therefore initiated an approach wherebysingle crystals of two different (K, Ba)16(Ga, Sn)136 compositions were first obtained, followed bygrinding of the crystals into fine powder for low temperature spark plasma sintering consolidationinto dense polycrystalline solids and subsequent high temperature transport measurements. PowderX-ray refinement results indicate that the hexakaidecahedra are empty, K and Ba occupying onlythe decahedra. Their electrical properties depend on composition and have very low thermalconductivities. The structural and transport properties of these materials are compared to thatof other Sn clathrate-II compositions.