Thermoelectric properties of nanostructured (Pb 1-m Sn m Te) 1-x (PbS) x with Pb and Sb precipitates
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1044-U03-15
Thermoelectric properties of nanostructured (Pb1-mSnmTe) 1-x (PbS) x with Pb and Sb precipitates. Steven N. Girard1, Joseph R. Sootsman1, Chia-Her Lin2, John Androulakis2, and Mercouri G. Kanatzidis1 1 Chemistry, Northwestern University, Evanston, IL, 60208-3113 2 Chemistry, Michigan State University, East Lansing, MI, 48824 ABSTRACT We report the physical characterization and thermoelectric properties of (Pb0.95Sn0.05Te)0.92(PbS)0.08 containing excess Pb and Sb prepared using the matrix encapsulation technique. Samples of (Pb0.95Sn0.05Te)0.92(PbS)0.08 : Pb 0.5 - 4 at. % rapidly quenched from the melt show microscale Pb inclusions that increase the thermal conductivity while slightly increasing the power factor, compared to (Pb0.95Sn0.05Te)0.92(PbS)0.08. Samples of (Pb0.95Sn0.05Te)0.92(PbS)0.08 : Pb 0.5%, Sb 2% prepared using the same technique show microscale Sb and Pb inclusions that upon heating cause rapid PbS and Sb segregation from the PbTe matrix. This behavior significantly alters the microstructure and degrades the transport properties of the material. INTRODUCTION Advances in the nanostructuring of thermoelectric materials have increased the thermoelectric figure of merit ZT, defined as ZT= (S2σT/κ), where S is the Seebeck coefficient or thermoelectric power, σ is electrical conductivity, T is temperature and κ is thermal conductivity. One important feature of nanostructured thermoelectric materials is the reduction of total thermal conductivity κtot, which is the sum of the lattice κlat and electronic κelec thermal contributions. This reduction in thermal conductivity is a result of phonon scattering at the interfaces of nanoscale inclusions within the material.[1-5] We recently proposed matrix encapsulation[6] and spinodal decomposition/ nucleation and growth phenomena[7] as two useful approaches to nanostructure bulk thermoelectric materials. In the matrix encapsulation technique, a small concentration of a semi- or insoluble minor phase is introduced into the bulk matrix and nanostructuring is achieved through rapid quenching of the material from the melt.[6,8] Nanostructuring achieved through spinodal decomposition and nucleation and growth in the thermoelectric material (Pb1-mSnmTe)1-x(PbS)x at m=0.05, x=0.04, 0.08, 0.16 has been demonstrated as a method to obtain exceptional reduction in the lattice thermal conductivity and enhanced figure of merit. These systems are not solid solutions, but rather phase separate into distinct nanoscale PbTe and PbS regions that help scatter phonons while not significantly altering the flow of charge carriers. A ZT of ~1.5 was optimized for (Pb0.95Sn0.05Te)0.92(PbS)0.08.[7] Of particular interest in nanostructured bulk thermoelectric materials is the ability to affect the electronic transport of the material by altering the scattering parameter λ. Heremans et al. demonstrated that Pb nanoprecipitates within bulk PbTe can significantly increase the thermopower of the material by altering λ, however thermal conductivity was not reduced.[8] The aim of this
