Thermoelectric power of graphite intercalation compounds with iodine monobromide

Abstract

Graphite intercalation compounds (GICs) with interhalogens, iodine monochloride (ICl-GICs) and iodine monobromide (IBr-GICs), are acceptor-type materials. They have a layer structure, and consequently, their thermoelectric power (TEP) along the basal plane (in-plane) is quite different from that in the vertical direction (c-axis). The in-plane TEP shows an approximately linear temperature dependence at low temperatures, which is ascribed to the diffusion term, and levels off above 200 K. This behavior stems from a phonon drag effect. However, the c-axis TEP shows approximately linear temperature dependence, which is a characteristic feature of the diffusion term. By choosing an appropriate set of parameters, the theory developed by Sugihara is found to give good agreement with the observed TEP results. We discuss the similarities and differences of both in-plane and c-axis TEP of IBr-GICs and ICl-GICs.