Thermoelectric properties of partially filled skutterudites RxCo4Sb12 (R = Ce and Nd) synthesized under high pressures

We report the thermoelectric properties of the partially Ce or Nd filled skutterudite compounds CexCo4Sb12 and NdxCo4Sb12 prepared under high pressures and temperatures. The samples were characterized by X-ray diffraction. The actual filling ratio x of Ce or Nd was estimated by scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDX). SEM-EDX results indicate that the maximum x values of Ce and Nd can be increased to 0.37 and 0.33, respectively. These values have been considered the highest for any CexCo4Sb12 and NdxCo4Sb12 reported thus far. The electrical resistivity, thermal conductivity, and Seebeck coefficient measurements of the compounds were performed from 5 to 760 K. Furthermore, the Hall coefficient and specific heat of the compounds were also measured below 300 K. The Seebeck and Hall coefficients of both Ce- and Nd-filled samples exhibited the n-type conductor behavior. The maximum dimensionless figure-of-merit (ZT) values of CexCo4Sb12 and NdxCo4Sb12 were determined to be 0.26 and 0.48 at 700K, respectively. (C) 2018 The Japan Society of Applied Physic

Thermoelectric Properties of As-Based Zintl Compounds Ba_1–<i>x</i>K_<i>x</i>Zn₂As₂

As-based Zintl compounds Ba_1–<i>x</i>K_<i>x</i>Zn₂As₂ were prepared by solid-state reaction followed by hot pressing. Ba_1–<i>x</i>K_<i>x</i>Zn₂As₂ (<i>x</i> ≤ 0.02) crystallizes in the α-BaCu₂S₂-type structure (space group <i>Pnma</i>) upon cooling from 900 °C, whereas it crystallizes in the ThCr₂Si₂-type structure (space group <i>I</i>4<i>/mmm</i>) for <i>x</i> ≥ 0.04. The lattice thermal conductivities are almost equivalent for both crystal structures with relatively low values of 0.8–1.1 W/mK at 773 K. The values are comparable to those of Sb-based Zintl compounds, though Ba_1–<i>x</i>K_<i>x</i>Zn₂As₂ consists of As atoms, which are lighter than Sb atoms. The electrical resistivity and Seebeck coefficient decreases with increasing <i>x</i>, indicating successful hole doping by K substitution. The dimensionless figure-of-merit ZT is 0.67 at 900 K for <i>x</i> = 0.02, opening a new class of thermoelectric materials with the As-based 122 Zintl compounds

Microstructural Control and Thermoelectric Properties of Misfit Layered Sulfides (LaS)_1+<i>m</i>TS₂ (T = Cr, Nb): The Natural Superlattice Systems

We investigated the high-temperature thermoelectric properties of misfit layered <i>n</i>-type (LaS)_1.20CrS₂ and <i>p</i>-type (LaS)_1.14NbS₂. The samples were prepared by CS₂ sulfurization of 6 or 12 h duration and then consolidated using pressure-assisted sintering to produce randomly and highly oriented samples whose microstructures were tunable. Transmission electron microscopy analysis showed that perfectly layered structures containing some stacking faults had formed. The randomly and highly oriented natural superlattices provided ultralow lattice thermal conductivities (as low as ∼0.9 and ∼0.5 W K^–1 m^–1, respectively, at 950 K) perpendicular to the pressing axis. The improved electrical conductivities of the oriented CrS₂ and NbS₂ samples resulted in high power factors of 170 and 410 μW K^–2 m^–1, respectively. The highly oriented texture produced the highest thermoelectric figure of merit <i>ZT</i> of 0.14 at 950 K among the (LaS)_1.20CrS₂ system, whereas the weakly/randomly oriented texture produced the highest <i>ZT</i> of 0.15 at 950 K among the (LaS)_1.14NbS₂ system. These misfit layered sulfides exhibit phonon glass–electron crystal behavior and provide tremendous opportunities for further enhancing <i>ZT</i> by optimizing the thermoelectric properties

Thermoelectric properties of partially filled skutterudites RxCo4Sb12 (R = Ce and Nd) synthesized under high pressures

application/pdfWe report the thermoelectric properties of the partially Ce or Nd filled skutterudite compounds CexCo4Sb12 and NdxCo4Sb12 prepared under high pressures and temperatures. The samples were characterized by X-ray diffraction. The actual filling ratio x of Ce or Nd was estimated by scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDX). SEM-EDX results indicate that the maximum x values of Ce and Nd can be increased to 0.37 and 0.33, respectively. These values have been considered the highest for any CexCo4Sb12 and NdxCo4Sb12 reported thus far. The electrical resistivity, thermal conductivity, and Seebeck coefficient measurements of the compounds were performed from 5 to 760 K. Furthermore, the Hall coefficient and specific heat of the compounds were also measured below 300 K. The Seebeck and Hall coefficients of both Ce- and Nd-filled samples exhibited the n-type conductor behavior. The maximum dimensionless figure-of-merit (ZT) values of CexCo4Sb12 and NdxCo4Sb12 were determined to be 0.26 and 0.48 at 700K, respectively. (C) 2018 The Japan Society of Applied Physic