Analysis of Ce- and Yb-Doped TAGS-85 Materials with Enhanced Thermoelectric Figure of Merit

Authors

  • E. M. Levin,

    Corresponding author
    1. Division of Materials Sciences and Engineering, Ames Laboratory of US DOE, Iowa State University, Ames, IA 50011–3020, USA
    2. Department of Physics and Astronomy, Iowa State University, Ames, IA 50011–3020, USA
    • Division of Materials Sciences and Engineering, Ames Laboratory of US DOE, Iowa State University, Ames, IA 50011–3020, USA.
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  • B. A. Cook,

    1. Division of Materials Sciences and Engineering, Ames Laboratory of US DOE, Iowa State University, Ames, IA 50011–3020, USA
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  • J. L. Harringa,

    1. Division of Materials Sciences and Engineering, Ames Laboratory of US DOE, Iowa State University, Ames, IA 50011–3020, USA
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  • S. L. Bud’ko,

    1. Division of Materials Sciences and Engineering, Ames Laboratory of US DOE, Iowa State University, Ames, IA 50011–3020, USA
    2. Department of Physics and Astronomy, Iowa State University, Ames, IA 50011–3020, USA
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  • R. Venkatasubramanian,

    1. Center for Solid State Energetics, RTI, International, Research Triangle Park, NC 27709, USA
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  • K. Schmidt-Rohr

    1. Division of Materials Sciences and Engineering, Ames Laboratory of US DOE, Iowa State University, Ames, IA 50011–3020, USA
    2. Department of Chemistry, Iowa State University, Ames, IA 50011–3020, USA
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Abstract

Doping of TAGS-85 with 1 at% Ce or Yb forms a dilute magnetic semiconductor system with non-interacting localized magnetic moments that obey the Curie law. X-ray diffraction patterns and slight broadening in 125Te NMR, attributed to paramagnetic effects, suggest that Ce and Yb atoms are incorporated into the lattice. 125Te NMR spin-lattice relaxation and Hall effect show similar hole concentrations of ≈1021 cm−3. At 700 K, the electric conductivity of the Ce- and Yb-doped samples is similar to that of neat TAGS-85, while the thermal conductivity and the Seebeck coefficient are larger by 6% and 16%, respectively. Possible mechanisms responsible for the observed increase in thermopower may include i) formation of resonance states near the Fermi level and ii) carrier scattering by lattice distortions and/or by paramagnetic ions. Due to the increase in the Seebeck coefficient up to 205 μV K−1, the thermoelectric power factor of Ce- and Yb-doped samples reaches 36 μW cm−1 K−2, which is larger than that measured for neat TAGS-85, 27 μW cm−1 K−2. The increase in the Seebeck coefficient overcomes the increase in the thermal conductivity, resulting in a total increase of the figure of merit by ≈25% at 700 K compared to that observed for neat TAGS-85.

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