Improved thermoelectric properties of AgSbTe2 based compounds with nanoscale Ag2Te in situ precipitates (original) (raw)
Related papers
Journal of Nanoscience and Nanotechnology, 2017
We report on rapid solidification of an Ag 16 7 Sb 30 0 Te 53 3 compound using planar flow casting to stabilize the-AgSbTe 2 single phase and avoid precipitation of the interconnected Sb 2 Te 3 phase, which leads to deterioration of thermoelectric properties. Rapidly solidified samples are in form of flakes with different thickness (60-400 m). Precipitation of Sb 2 Te 3 phase is fully inhibited in thin flakes (thickness below 100 m), which consist of an homogeneous-AgSbTe 2 matrix, whereas isolated Sb 2 Te 3 precipitates, dispersed throughout the-AgSbTe 2 matrix, were found in thick flakes (thickness above 100 m). The lattice parameter of the-AgSbTe 2 phase progressively increases with the cooling rate, indicating progressive supersaturation of the matrix for high degree of supercooling. Bulk specimens were prepared by hot pressing of the rapidly solidified flakes to evaluate thermoelectric properties. After sintering of the rapidly solidified flakes, the differential scanning calorimetry (DSC) traces indicates partial decomposition of the non equilibrium-AgSbTe 2 into the stable phases. Measurements of the thermoelectric transport properties indicate the positive effects of rapid solidification on thermal conductivity and Seebeck coefficient and its negative effect on electrical conductivity, suggesting an operative way to improve thermoelectric performance.
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.
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.
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.
Enhanced thermoelectric performance in Bi-doped p-type AgSbTe 2 compounds
2013
The influence of bismuth (Bi) substitution on the thermoelectric properties of AgSbTe 2 compounds was investigated and compared with the undoped AgSbTe 2. The addition of Bi dopants not only resulted in a reduction in thermal conductivity but also markedly increased the thermopower in the Ag(Sb 1Àx Bi x)Te 2 series. Additional phonon scatterings were created by Bi doping and led to a reduction of thermal conductivity. The lattice thermal conductivity is significantly reduced which could be ascribed to enhancement of phonon scattering by dopants with greater atomic weight. In addition, the thermopower was enhanced, which was attributed to the electron-filtering effects caused by the nanoscaled microstructures. Because of the extremely low thermal conductivity (0.48 Wm À1 K À1) and moderate power factor of AgBi 0.05 Sb 0.95 Te 2 , a maximum ZT value of (1.04 6 0.08) was reached at 570 K; yielding an enhancement of greater than 10% compared with an undoped AgSbTe 2. this result shows promising thermoelectric properties in the medium temperature range. V
arXiv (Cornell University), 2023
The present study demonstrates a large enhancement in the Seebeck coefficient and ultralow thermal conductivity (TE) in Sb 2 Te 3-AgSbTe 2 nanocomposite thin film. The addition of Ag leads to the in-situ formation of AgSbTe 2 secondary phase nano-aggregates in the Sb 2 Te 3 matrix during the growth resulting in a large Seebeck coefficient and reduction of the thermal conductivity. A series of samples with different amounts of minor AgSbTe 2 phases are prepared to optimize the TE performance of Sb 2 Te 3 thin films. Based on the experimental and theoretical evidence, it is concluded that a small concentration of Ag promotes the band flattening and induces a sharp resonatelike state deep inside the valence band of Sb 2 Te 3 , concurrently modifying the density of states (DOS) of the composite sample. In addition, the electrical potential barrier introduced by the band offset between the host TE matrix and the secondary phases promotes strong energy-dependent carrier scattering in the composite sample, which is also responsible for enhanced TE performance. A contemporary approach based on scanning thermal microscopy is performed to experimentally obtain thermal conductivity values of both the in-plane and cross-plane directions, showing a reduced in-plane thermal conductivity value by ~ 58% upon incorporating the AgSbTe 2 phase in the Sb 2 Te 3 matrix. Benefitting from the synergistic manipulation of electrical and thermal transport, a large ZT value of 2.2 is achieved at 375 K. The present study indicates the importance of a combined effect of band structure modification and energy-dependent charge carrier scattering along with reduced thermal conductivity for enhancing TE properties.
SnTe–AgBiTe 2 as an efficient thermoelectric material with low thermal conductivity
J. Mater. Chem. A, 2014
SnTe–AgBiTe2 is not only a solid solution but a nanocomposite. The alloying effect coupled with intense interface scattering leads to considerably decreased lattice thermal conductivity. Bi is much more powerful in neutralizing holes than Sb, giving rise to a much higher Seebeck coefficient. A high ZT was then obtained.
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