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1044-U06-12

Thermoelectric Properties of La-doped BaSi2 and (Ba,Sr)Si2 Solid Solutions Kohsuke Hashimoto, Ken Kurosaki, Hiroaki Muta, and Shinsuke Yamanaka Division of Sustainable Energy and Environmental Engineering, Graduate School of Engineering, Osaka University, Yamadaoka 2-1, Suita, 565-0871, Japan ABSTRACT We studied the thermoelectric properties of BaSi2 and SrSi2. The polycrystalline samples were prepared by spark plasma sintering (SPS). The electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) were measured above room temperature. The maximum values of the dimensionless figure of merit (ZT) were 0.01 at 954 K for BaSi2 and 0.09 at 417 K for SrSi2. We tried to enhance the ZT values of BaSi2 and SrSi2 by preparing and characterizing Ladoped BaSi2 and (Ba,Sr)Si2 solid solution. INTRODUCTION Thermoelectric materials are capable of convert waste heat into usable electricity [1]. The effectiveness of a material for thermoelectric applications is determined by the dimensionless figure of merit, ZT = (S2/ρ)T/κ, where S is the Seebeck coefficient, σ the electrical conductivity, κ the thermal conductivity, and T the absolute temperature [2]. The electrical properties are determined by the power factor, defined as S2σ or S2/ρ, where ρ is the electrical resistivity. The ZT value of the materials used in current devices is approximately 1. However, present highperformance thermoelectric materials consist of toxic and/or rare elements such as bismuth and tellurium. Semiconductor metal silicides have attracted attention as candidates of new thermoelectric materials because they are environmentally friendly. For example, the thermoelectric properties of FeSi2 and Mg2Si have been widely studied, and an excellent ZT value (= 1.1) was achieved in the n-type Mg2(Si,Sn) system [3]. However, other alkaline-earth silicides, especially the silicides of barium and strontium, have been less explored as thermoelectric materials. Recently, BaSi2 has been studied as a potential candidate for thin-film solar cell material, because it has a large absorption coefficient and a suitable band gap energy (1.13 eV) [4,5]. SrSi2 has been found to be a detector of infrared rays, because it has a narrow band gap energy (0.035 eV) [6]. At atmospheric pressure and room temperature, BaSi2 and SrSi2 crystallize with the orthorhombic BaSi2-type structure (space group: Pnma) and the cubic SrSi2type structures (space group: P4332), respectively [7]. In this paper, we investigated the thermoelectric properties above room temperature of the semiconductor alkaline-earth silicides: BaSi2 and SrSi2. Furthermore, we tried to improve the thermoelectric properties of BaSi2 and SrSi2. EXPERIMENT Polycrystalline samples of BaSi2, SrSi2, La-doped BaSi2, i.e., Ba1-xLaxSi2 (x = 0.02, 0.04, 0.08), and (Ba,Sr)Si2 solid solution, i.e., BaxSr1-xSi2 (x = 0.04), were prepared by spark plasma sintering (SPS). BaSi2 (>99 %, lumps), SrSi2 (>99 %, powder), LaSi (>99.9 %, powder), and Si

(>99 %, powder) were used as starting materials. The start