Zintl Phase as Thermoelectric Materials: Synthesis, Structure and Properties of Yb 5 Al 2 Sb 6

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1044-U06-01

Zintl Phase as Thermoelectric Materials: Synthesis, Structure and Properties of Yb5Al2Sb6 Iliya Todorov1, Duck-Young Chung1, and Mercouri Kanatzidis1,2 1 Materials Science Division, Argonne National Laboratory, 9700 S. Cass Ave., Argonne, IL, 60439 2 Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208 ABSTRACT We present the synthesis, crystal structure, spectroscopic properties, and electronic structure of a new member of the Zintl family, Yb5Al2Sb6. The compound crystallizes in the Ba5Al2Bi6 structure type. A preliminary assessment of its thermoelectric properties including electrical conductivity, thermopower, and thermal conductivity are reported. Moreover, investigations of solid solutions of this phase, doping effects and chemical modifications will be presented. The room temperature conductivity, thermopower and thermal conductivity of Yb5Al2Sb6/0.5Ge were 1100 S/cm, 20 ┬ÁV/K, and 3.8 W/m.K, respectively. INTRODUCTION In recent years considerable attention has been paid on intermetallic compounds as a new candiate of theremoelectric materials. Specifically, electronically balanced Zintl phase system possess thermal stability at very high temperature, fairly small band gap, complex anionic frameworks stabilized by weakly bounded electropositive cations and thus low lattice thermal conductivity [1]. Zintl phases are an understudied class of compounds for high temperature thermoelectric applications despite their compositional and structural diversity. A major drawback of this class of compounds is that most of them are air- and moisture sensitive primarily due to the highly electropositive elements, such as alkali, alkaline-earth metals and the elements with unusual oxidation states. However, substitution of these elements in particular system of interest with proper rare-earth metals may drastically improve the stability of these compounds [2]. Also, in some intermetallic materials, the f-electrons of rare-earth elements are known to be responsible for unusual electronic transport properties, especially, high thermopower [3]. A recent successful example from the Zintl class of compounds is Yb14MnSb11.8 [4]. This compound has demonstrated the thermoelectric figure of merit ZT of 1.0 at 1223 K. This finding provides a strong indication that this class of materials could be full of new thermoelectric candidates. Here we describe the structure of new member of the Zintl family, Yb5Al2Sb6. The compound crystallizes in the Ba5Al2Bi6 structure type and is isostructural and isoelectronic to the recently reported Yb5In2Sb6 [5]. Investigations of phase formation, chemical modifications, and doping effects on this compound and the preliminary charge transport property and thermal conductivity are also discussed. EXPERIMENT Initially, Yb5Al2Sb6 was found as a minor phase from reaction with nominal composition YbAlSbGe. After the stoichiometry of the compound was elucidated from its structure determination, the new compound Yb5Al2Sb6 was synthesized as single phase. The sta