Electronic transport properties of pnictogen-substituted skutterudites with alkaline-earth fillers
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Electronic transport properties of pnictogen-substituted skutterudites with alkaline-earth fillers Semi Bang1, An Li2, Dae Hyun Wee1,*, Marco Fornari3, and Boris Kozinsky2 1
Department of Environmental Science and Engineering, Ewha Womans University, Seoul, 120-
750, Korea. 2
Research and Technology Center, Robert Bosch LLC, Cambridge, MA, U.S.A.
3
Department of Physics, Central Michigan University, Mt. Pleasant, MI, U.S.A.
* Corresponding Author: [email protected] ABSTRACT The materials class of skutterudites is one of the promising thermoelectric materials due to its decent electronic properties and cage-like structural feature that can be filled with guest atoms. First principles calculations have been performed in order to investigate electronic band structures and related transport properties of pnictogen-substitued skutterudites filled with alkaline-earth elements (MxCo4A6Te6 where M=Ca, Sr, or Ba, A=Ge or Sn, and x=0.5 or 1). The Seebeck coefficient and the power factor, which are electronic transport properties related to thermoelectricity, are computed by using the Boltzmann transport formalism within the constantrelaxation-time-approximation. The results are compared against the corresponding properties of the unfilled pnictogen-substitued ternary skutterudites (CoA1.5Te1.5) to identify the effects of filling, based on which the potential of filled pnictogen-substituted skutterudites for thermoelectric applications is evaluated. The possible changes in the ionic character of the interatomic bonding, which was suspected to be an important scattering source, are probed by analyzing the projected density of states. INTRODUCTION Thermoelectric materials can be used for recovering waste heat energy by directly converting heat to electricity. Such thermoelectric electricity generation may be realized in a relatively compact power generation system compared to conventional heat engines, since the direct conversion through thermoelectric materials does not require any moving part, resulting in a fully solid-state device. Potential and present applications of thermoelectric materials include waste heat recovery in vehicles, spot cooling in computers or in other small-scales electronic devices. However, despite all the advantages of thermoelectric materials, their low energy conversion efficiency greatly limits their range of applications [1]. It remains an important task for the research community to discover new thermoelectric materials or to enhance the performance of existing thermoelectric materials in order to realize the full potential of thermoelectric energy conversion. The dimensionless figure of merit ZT is used as an indicator of thermoelectric performance of a material. ZT is defined as ZT=S2σT/κ, where S is Seebeck coefficient, σ is the electrical conductivity, and κ is the total thermal conductivity, which is typically given by κ = κL (lattice thermal conductivity) + κe (electronic thermal conductivity). As suggested by the formula, a high power factor S2σ and a small thermal conductivity κ are b
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