High-temperature transport properties of complex antimonides with anti-Th3P4 structure

Polycrystalline samples of R4Sb3 (R = La, Ce, Smand Yb) and Yb4-xR¢xSb3 (R¢ = Sm and La) have been quantitatively synthesized by high-temperature reaction. They crystallize in the anti-Th3P4 structure type (I ¯43d, no. 220). Structural and chemical characterizations have been performed by X-ray diffraction and electron microscopy with energy dispersive X-ray analysis. Powders have been densified by spark plasma sintering (SPS) at 1300 ◦C under 50 MPa of pressure. Transport property measurements show that these compounds are n-type with low Seebeck coefficient except for Yb4Sb3 that shows a typical metallic behavior with hole conduction. By partially substituting Yb by a trivalent rare earth we successfully improved the thermoelectric figure of merit of Yb4-xR¢xSb3 up to 0.75 at 1000 ◦C

High efficiency thermoelectric power generation using Zintl-type materials

The invention disclosed herein relates to thermoelectrically-active p-type Zintl phase materials as well as devices utilizing such compounds. Such thermoelectric materials and devices may be used to convert thermal energy into electrical energy, or use electrical energy to produce heat or refrigeration. Embodiments of the invention relate to p-type thermoelectric materials related to the compound Yb.sub.14MnSb.sub.11

Yb14MnSb11 as a High-Efficiency Thermoelectric Material

Yb14MnSb11 has been found to be wellsuited for use as a p-type thermoelectric material in applications that involve hotside temperatures in the approximate range of 1,200 to 1,300 K. The figure of merit that characterizes the thermal-to-electric power-conversion efficiency is greater for this material than for SiGe, which, until now, has been regarded as the state-of-the art high-temperature ptype thermoelectric material. Moreover, relative to SiGe, Yb14MnSb11 is better suited to incorporation into a segmented thermoelectric leg that includes the moderate-temperature p-type thermoelectric material CeFe4Sb12 and possibly other, lower-temperature p-type thermoelectric materials. Interest in Yb14MnSb11 as a candidate high-temperature thermoelectric material was prompted in part by its unique electronic properties and complex crystalline structure, which place it in a class somewhere between (1) a class of semiconducting valence compounds known in the art as Zintl compounds and (2) the class of intermetallic compounds. From the perspective of chemistry, this classification of Yb14MnSb11 provides a first indication of a potentially rich library of compounds, the thermoelectric properties of which can be easily optimized. The concepts of the thermoelectric figure of merit and the thermoelectric compatibility factor are discussed in Compatibility of Segments of Thermo - electric Generators (NPO-30798), which appears on page 55. The traditional thermoelectric figure of merit, Z, is defined by the equation Z = alpha sup 2/rho K, where alpha is the Seebeck coefficient, rho is the electrical resistivity, and k is the thermal conductivity

Thermoelectric Higher Manganese Silicide: Synthetized, sintered and shaped simultaneously by selective laser sintering/Melting additive manufacturing technique

Complex geometry legs were advantageous to obtain higher thermoelectric potential due to a better thermal dissipation. Among all industrial processes, additive manufacturing using a selective laser sintering (SLS) or melting (SLM) techniques is the most promising to obtain such complex-shape legs without machining step. In this work, for the first time, Higher Manganese Silicide (HMS) sheet samples were synthetized, sintered and shaped simultaneously by additive manufacturing from ball milled manganese and silicon powder. Impact of surface power density and scanning rate of the laser on the microstructural and structural properties was discussed for some SLS/M parameters. Characterizations have shown that both densification and pure HMS phase can be obtained by SLS/M

Thermoelectric Inhomogeneities in (Ag(sub 1-y)SbTe2)(sub x)(PbTe)(sub 1-x)

A document presents a study of why materials of composition (Ag1 ySbTe2)0.05 (PbTe)0.95 [02. In the study, samples of (AgSbTe2)0.05(PbTe)0.95, (Ag0.67SbTe2)0.05 (PbTe)0.95, and (Ag0.55SbTe2)0.05(PbTe)0.95 were prepared by melting followed, variously, by slow or rapid cooling. Analyses of these samples by x-ray diffraction, electron microscopy, and scanning-microprobe measurements of the Seebeck coefficient led to the conclusion that these materials have a multiphase character on a scale of the order of millimeters, even though they appear homogeneous in x-ray diffraction and electron microscopy. The Seebeck measurements showed significant variations, including both n-type and p-type behavior in the same sample. These variations were found to be consistent with observed variations of ZT. The rapidly quenched samples were found to be less inhomogeneous than were the furnace-cooled ones; hence, rapid quenching was suggested as a basis of research on synthesizing more nearly uniform high-ZT samples

Stability and thermoelectric performance of doped higher manganese silicide materials solidi fied by RGS (ribbon growth on substrate) synthesis

Large scale deployment of thermoelectric devices requires that the thermoelectric materials have stable electrical, thermal and mechanical properties under the conditions of operation. In this study we examine the high temperature stability of higher manganese silicide (HMS) materials prepared by the RGS (ribbon growth on substrate) technique. In particular we characterize the effect of element substitution on the structural and electrical changes occurring at the hot side of temperatures of thermoelectric devices relevant to this material (600°C). Only by using suitable substitution (4% vanadium at the Mn site) can we obtain temperature-independent structural parameters in the range 20°C - 600°C, a condition that results in stable electrical properties. Additionally, we show that 4% vanadium substitution at the Mn site offers the best thermoelectric figure of merit among the different compositions reported here with ZTmax=0.52, a value comparable to the state of the art for HMS materials. Our analysis suggests that ionized impurity scattering is responsible for the better performance of this material

Improved Thermoelectric Performance in Yb_(14)Mn_(1−x)Zn_xSb_(11) by the Reduction of Spin-Disorder Scattering

Rare-earth transition metal compounds Yb_(14)Mn_(1−x)Zn_xSb_(11), isostructural with Ca_(14)AlSb_(11), have been prepared using a metal flux growth technique for thermoelectric property measurements (with x = 0.0, 0.2, 0.3, 0.4, 0.7, 0.9, and 1.0). Single-crystal X-ray diffraction and electron microprobe analysis data indicate the successful synthesis of a solid-solution for the Yb_(14)Mn_(1−x)Zn_xSb_(11) structure type for 0 0.4. High-temperature (298 K–1275 K) measurements of the Seebeck coefficient, resistivity, and thermal conductivity were performed on hot-pressed, polycrystalline samples. As the concentration of Zn increases in Yb_(14)Mn_(1−x)Zn_xSb_(11), the Seebeck coefficient remains unchanged for 0 ≤ x ≤ 0.7 indicating that the free carrier concentration has remained unchanged. However, as the nonmagnetic Zn^(2+) ions replace the magnetic Mn^(2+) ions, the spin disorder scattering is reduced, lowering the resistivity. Replacing the magnetic Mn^(2+) with non magnetic Zn^(2+) provides an independent means to lower resistivity without deleterious effects to the Seebeck values or thermal conduction. Alloying the Mn site with Zn reduces the lattice thermal conductivity at low temperatures but has negligible impact at high temperatures. The reduction of spin disorder scattering leads to an ∼10% improvement over Yb_(14)MnSb_(11), revealing a maximum thermoelectric figure of merit (zT) of ∼1.1 at 1275 K for Yb_(14)Mn_(0.6)Zn_(0.4)Sb_(11)

Improved Thermoelectric Performance in Yb_(14)Mn_(1−x)Zn_xSb_(11) by the Reduction of Spin-Disorder Scattering

Rare-earth transition metal compounds Yb_(14)Mn_(1−x)Zn_xSb_(11), isostructural with Ca_(14)AlSb_(11), have been prepared using a metal flux growth technique for thermoelectric property measurements (with x = 0.0, 0.2, 0.3, 0.4, 0.7, 0.9, and 1.0). Single-crystal X-ray diffraction and electron microprobe analysis data indicate the successful synthesis of a solid-solution for the Yb_(14)Mn_(1−x)Zn_xSb_(11) structure type for 0 0.4. High-temperature (298 K–1275 K) measurements of the Seebeck coefficient, resistivity, and thermal conductivity were performed on hot-pressed, polycrystalline samples. As the concentration of Zn increases in Yb_(14)Mn_(1−x)Zn_xSb_(11), the Seebeck coefficient remains unchanged for 0 ≤ x ≤ 0.7 indicating that the free carrier concentration has remained unchanged. However, as the nonmagnetic Zn^(2+) ions replace the magnetic Mn^(2+) ions, the spin disorder scattering is reduced, lowering the resistivity. Replacing the magnetic Mn^(2+) with non magnetic Zn^(2+) provides an independent means to lower resistivity without deleterious effects to the Seebeck values or thermal conduction. Alloying the Mn site with Zn reduces the lattice thermal conductivity at low temperatures but has negligible impact at high temperatures. The reduction of spin disorder scattering leads to an ∼10% improvement over Yb_(14)MnSb_(11), revealing a maximum thermoelectric figure of merit (zT) of ∼1.1 at 1275 K for Yb_(14)Mn_(0.6)Zn_(0.4)Sb_(11)

Robust, Transparent Hybrid Thin Films of Phase-Change Material Sb2S3 Prepared by Electrophoretic Deposition

Thin films of polyethylenimine-stabilized Sb2S3 are prepared via electrophoretic deposition (EPD), showing strong adhesion between the deposited layers and the underlying substrate, with the films being crystallized via annealing. For amorphous films, thicknesses can be freely tuned from 0.2 to 1 μm, shrinking to 0.1–0.5 μm when crystallized, while retaining a crack- and defect-free surface, thus not impacting their good stability and maintaining their optical properties. Through UV–vis spectroscopy and subsequent modeling of the obtained spectra, it was concluded that the materials after annealing showed a reduced band gap and a demonstrably increased refractive index (n) and carrier concentration. The use of EPD for this material shows the viability of rapidly creating stable thin films of phase-change materials

Measuring thermoelectric transport properties of materials

In this review we discuss considerations regarding the common techniques used for measuring thermoelectric transport properties necessary for calculating the thermoelectric figure of merit, zT. Advice for improving the data quality in Seebeck coefficient, electrical resistivity, and thermal conductivity (from flash diffusivity and heat capacity) measurements are given together with methods for identifying possible erroneous data. Measurement of the Hall coefficient and calculation of the charge carrier concentration and mobility is also included due to its importance for understanding materials. It is not intended to be a complete record or comparison of all the different techniques employed in thermoelectrics. Rather, by providing an overview of common techniques and their inherent difficulties it is an aid to new researchers or students in the field. The focus is mainly on high temperature measurements but low temperature techniques are also briefly discussed