Thermoelectric Properties of the Pseudobinary Alloy (Ag0.365Sb0.558Te)0.975(GeTe)0.025 Prepared by Spark Plasma Sintering (original) (raw)
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Phase equilibria of Ag–Sb–Te thermoelectric materials
Acta Materialia, 2011
The ternary Ag-Sb-Te system is important for thermoelectric applications because the AgSbTe 2 ternary compound has a high figureof-merit and because Ag-Sb-Te is a subsystem of the very promising quaternary Pb-Ag-Sb-Te thermoelectric alloys. In this study we prepared equilibrated Ag-Sb-Te ternary alloys at 250 and 400°C. These alloys were metallographically examined, and their microstructures and equilibrium phases were determined. Based on the phase equilibria information available in the literature and the experimental results determined in this study, the isothermal sections of the ternary Ag-Sb-Te system at 250 and 400°C were constructed. The AgSbTe 2 compound is stable at 400°C but not at 250°C. Moreover, high-resolution transmission electronic microscopy images of the ternary AgSbTe 2 compound and its crystal structure were determined. The crystal structure of AgSbTe 2 is rock salt (NaCl type), and its homogeneous compositional regime is determined to be 49.0-53.0 at.% Te and 28.0-30.0 at.% Sb. The solubilities of Ag in the Sb-Te binary compounds, c and d, at 400°C are as high as 8.6 and 5.7 at.%, respectively.
Fabrication of Ag–Sn–Sb–Te based thermoelectric materials by MA-PAS and their properties
Starting from elemental powder mixtures of AgSn 18 SbTe 20 and Sn 50 Te 50 , P-type AgSn 18 SbTe 20 and Sn 50 Te 50 bulk thermoelectric materials were fabricated by a combined process of mechanical alloying (MA) and plasma activated sintering (PAS). It was found that SnTe compound could be easily synthesized after milling only for 1 h. Prolonging the milling time, Ag and Sb atoms diffused into the lattice of the primary SnTe compound gradually and SnTe-based solid solution was formed. The electrical resistivity and Seebeck coefficient of the as-PASed samples were measured from 323 K to 723 K. The maximum power factor of 1.98 × 10 −3 Wm −1 K −2 was obtained at 673 K for AgSn 18 SbTe 20 and it was higher than that of the material with similar composition from previous published literature.
Preparation and thermoelectric properties of AgPb m SbTe 2+ m alloys
Journal of Alloys and Compounds, 2009
Hydrothermally synthesized AgPbmSbTe2+m (m=10–18) nanopowders were pressure-less sintered at 450–480°C for 5h in Ar. The samples show large positive Seebeck coefficient but low electrical conductivity and the AgPb18SbTe20 sample shows higher power factors. The hot pressed AgPb10SbTe12 sample was highly densified with grain size down to nanoscale, and the sample has inhomogeneous Seebeck coefficient. Obviously different thermoelectric properties have been
a b s t r a c t (GeTe) x (AgSbTe 2 ) 100Àx : TAGS thermoelectrics are an attractive class of materials due to their combination of non-toxicity and good conversion efficiency at mid-temperature ranges. In the present work, we have utilized energy and time efficient high-pressure gas atomization and spark-plasma sintering techniques for large-scale preparation of samples with varying composition (i.e., (GeTe) x (AgSbTe 2 ) 100Àx where x ¼ 75, 80, 85, and 90). High-temperature x-ray diffraction was used to understand the phase transformation mechanism of the as-atomized powders. Detailed high-resolution transmission electron microscopy of the sintered samples revealed the presence of nanoscale precipitates, antiphase, and twin boundaries. The nanoscale twins and antiphase boundaries serve as phonon scattering centers, leading to the reduction of total thermal conductivity in TAGS-80 and 90 samples. The maximum ZT obtained was 1.56 at 623 K for TAGS-90, which was~94% improvement compared to values previously reported. The presence of the twin boundaries also resulted in a high fracture toughness (K IC ) of the TAGS-90 sample due to inhibition of dislocation movement at the twin boundary.
Reduced thermal conductivity in Pb-alloyed AgSbTe2 thermoelectric materials
Acta Materialia, 2012
Pb-alloyed AgSbTe 2 (Pb x Ag 20 Sb 30Àx Te 50 (x = 3, 4, 5 and 6)) composites were synthesized using a modified Bridgman method with a graphite mold to form plate-like samples. The Bridgman-grown specimens were dense, with few solidification cavities, and were sufficiently mechanically robust for a variety of electronic/thermal transport measurements. Inhomogeneity was found on the grain boundary, and was embedded with the nanoprecipitates of d-Sb 2 Te with a feature size of 100 nm of the 5 at.% Pb and 6 at.% Pb specimens. A combined effect of alloying, inhomogeneity and nanoprecipitates leads to a low thermal conductivity of 0.3-0.4 W m À1 K À1 , which approaches the theoretical minimum thermal conductivity of the amorphous material (j min $ 0.36 W m À1 K À1 ). A peak of the zT value, ranging from 0.7 to 0.8, is achieved at 425 K. Further annealing at 673 K increases the grain size and causes a reduction in the value of the zT peak to 0.4.
In this work, it is demonstrated that a higher electrical conductivity can be obtained when Ag atoms, as a transition metal, replaces Bi atoms in the n-type Bi 2-x Ag x Se 3 system. As a result of differences in the atomic mass and size between Ag and Bi, larger Seebeck coefficient is obtained. The concerned Bi 2-x Ag x Se 3 alloys were prepared by melting in high temperature. Identifications of the microstructure and surface morphology were carried out via X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) attached with the energy dispersive x-ray (EDX) unit. All samples are polycrystalline. Seebeck coefficient, electrical and thermal conductivities were measured over the temperature range 300 e473K. Notable enhancement in the electrical conductivity is obtained. The thermoelectric power factor is calculated showing its maximum value at 260 mW/mK 2. High electrical conductivity and high Seebeck coefficient of some of the doped alloys resulted in a promising figure of merit (ZT). The largest ZT is calculated at 0.23 at 473K for the Bi 1.8 Ag 0.20 Se 3 sample.
Journal of Alloys and Compounds, 2010
Ternary Ag x Sb 2−x Te 3−x thermoelectric materials have been prepared with x value varying from 0.78 to 0.93. By adjusting the Ag 2 Te ratio, double-phased in situ nanocomposites were obtained with the nanostructured Ag 2 Te embedded in the AgSbTe 2 matrix when x > 0.81. The high-resolution transmission electron microscopy observation showed that the Ag 2 Te precipitates were in situ formed as nanodots and nanoscale lamellar structures. Compared with the single-phased samples of x = 0.78 and 0.81, the Seebeck coefficient of the nanocomposite samples exhibited significant improvement over the entire measured temperature range and the electrical conductivity also slightly increased, resulting in the increase of the power factor. At the same time, the thermal conductivity of the nanocomposite samples slightly decreased. The optimization of both the power factor and the thermal conductivity contributed to the notable improvement in figure of merit ZT by a factor of ∼40% at 670 K.
MRS Proceedings, 2005
The structural and thermoelectric properties of the AgSbTe 2 -SnTe quaternary system were studied. Powder averaged x-ray diffraction of Ag 0.85 SnSb 1.15 Te 3 indicates a cubic NaCltype structure in contrast with the single crystal refinements, which point towards tetragonal symmetry. Furthermore, high-resolution electron microscopy imaging revealed the system to be a nano-composite formed by thermodynamically driven compositional fluctuations rather than a solid solution as it was viewed in the past. The lattice thermal conductivity attains very low values, which is in accord with recent theories on thermal transport in heterogeneous systems. The charge transport properties of the system exhibit a rich physical behavior highlighted in the coexistence of an almost metallic carrier concentration (~5×10 21 cm -3 ) with a large thermoelectric power response of ~160 μV/K at 650 K. This is attributed to a heavy hole effective mass that is almost six times that of the electron rest mass.
Low-Temperature Thermoelectric Properties of β-Ag2Se Synthesized by Hydrothermal Reaction
Journal of Electronic Materials, 2011
β-Ag2Se is a narrow-bandgap semiconductor with a high electrical conductivity, reasonably large Seebeck coefficient, and low thermal conductivity. It is regarded as a potential candidate for thermoelectric applications. In this work, we prepared powders of β-Ag2Se by hydrothermal reaction at 180°C. The spark plasma sintering technique was employed to form compact samples. The thermoelectric properties were measured in a temperature range between 20 K and 350 K. A maximum figure of merit of over 0.6 was found around room temperature. Theoretical calculations were carried out to estimate the Seebeck coefficient of β-Ag2Se, reproducing the experimental trend qualitatively.