Electrical and thermoelectric properties of p-Ag2Te in the β phase

Aliev, F. A.

doi:10.1134/1.1610118

Cited by 16 publications

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“…This feature exhibits a hysteresis between heating up and cooling down measurements, and strengthens as the Ag 2 Te concentration is increased. This may result from the β → α , monoclinic-to-cubic phase transition of Ag 2 Te, [ 33 ] in which an obvious resistivity enhancement and other electrical transport abnormalities have been reported in the literature. [ 33 ] However, the effect of this transition on lattice thermal conductivity and Seebeck coeffi cient is very weak (Figure 8a & 9 c ).…”

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“…This is also evident from the quick crossover of the Seebeck coeffi cient as well as the Hall coeffi cient, as shown in Figure 3b for the Ag5.5 sample, indicating a typical mixed conduction by both electrons and holes. We speculate that the β → α , monoclinic to cubic, phase transition [ 33 ] of Ag 2 Te at this temperature (see Figure 1a ) might also be responsible for the resistivity peaks. One might expect Ag 2 Te to be a p-type dopant in PbTe in analogy to Na 2 Te and K 2 Te where Na + or K + substitute for Pb + 2 .…”

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High Thermoelectric Performance in PbTe Due to Large Nanoscale Ag2Te Precipitates and La Doping

et al. 2010

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wileyonlinelibrary.comAdv. Funct. Mater. 2011, 21, 241-249 the infl uence of nano-particle content, density and size, as well as the infl uence from alloy-scattering and electronic doping effects. In this article, we describe the controlled synthesis and thermoelectric properties of fi ne and uniformly dispersed Ag 2 Te precipitates embedded in PbTe. In contrast to many previously studied PbTe-based systems, [ 5 , 10 , 11 , 13-16 ] the Ag 2 Te precipitates are much larger (50-200 nm), are not isostructural to PbTe and do not introduce considerable electronic doping effect to PbTe. We show that these precipitates scatter the phonons effectively, leading to a low lattice thermal conductivity which approaches the minimum expected of PbTe above 650 K. Moreover, doping with La independently optimizes the carrier concentration and results in a thermoelectric fi gure of merit of 1.6 in La-doped PbTe-Ag 2 Te composites at 775 K. This value is about twice that of the state-of-the-art n-type PbTe [ 1 , 26 ] and arises from the low lattice thermal conductivity at this temperature. (PbTe)1 MicrostructureThe pseudo-binary phase diagram of PbTe-Ag 2 Te (see Figure 1 ) [27][28][29] shows signifi cant and strongly temperature dependent solubility of Ag 2 Te in PbTe. Similar behavior in the PbTe-Sb 2 Te 3 phase diagram has been harnessed to yield Widmanstätten precipitates of Sb 2 Te 3 in a matrix of PbTe. [ 25 ] Here, we utilize the variance in maximum solubility of Ag 2 Te in PbTe, which is about 7-11 mol.% [ 27 , 29 ] at the eutectic temperature of ∼ 970 K and quickly drops to about 1 mol.% at ∼ 770 K. [ 27 ] From these features, one can expect that after melting (step 1 in Figure 1 ) and homogenizing the solid solution at ∼ 970 K (step 2 in Figure 1 ), Ag 2 Te precipitates will be obtained during a lower temperature anneal at ∼ 770 K (step 3 in Figure 1 ).Four compositions of (PbTe) 1 − x (Ag 2 Te) x are considered here ( x = 1.3, 2.7, 4.1, 5.5), all of which have compositions ( Table 1 ) greater than the solubility limit for Ag 2 Te at the annealing temperature (770 K). Following this thermal treatment, Ag-rich precipitates are observed to be homogeneously distributed in the PbTe matrix, as shown by fi eld emission scanning electron microscopy images ( Figure 2 a ). As the Ag 2 Te content increases, the Ag 2 Te is incorporated as a solid solution in the PbTe matrix [27][28][29] ). The open circle at 773 K shows the experimental Ag solubility in PbTe, [ 27 ] consistent with the current study. Starting with a homogeneous melt at a composition of Ag5.5 (point 1), the sample is quenched and then annealed within the single phase region (point 2) for homogenization. Phase separation is then achieved by annealing at 773 K (point 3). up to the solubility limit ( ∼ 1%) at the annealing temperature. [ 27 ] Beyond the solubility limit, the volume fraction of Ag 2 Te particles increases with increasing Ag 2 Te content in the mixture (Figure 2 ), but the Ag content in the PbTe matrix remains constant. The solubility limit is dir...

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High Thermoelectric Performance in PbTe Due to Large Nanoscale Ag2Te Precipitates and La Doping

et al. 2010

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“…16 is the sign change of the Seebeck coefficient near 400 K for the pseudo-binary composite (PbTe) 1−x (Ag 2 Te) x . The two composites with different synthesis methods commonly have a dip feature of electrical conductivity (peak of electrical resistivity) near 420 K. One possible explanation for the decreased electrical conductivity and Seebeck coefficient near 420 K in the case of the PbTe/Ag 2 Te extrinsic composites is the α-(monoclinic) to β-(cubic) structural phase transition of Ag 2 Te at 415 K. 16,22 Below the temperature of the structure phase transition at 415 K, the Seebeck coefficient becomes n-type with decreasing electrical conductivity.…”

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“…22 The electronic band structure of α-Ag 2 Te with a strong Te 4p-Ag 4d hybridization shifts the Te 4p-orbital upward and pushes down the Ag 4d band, resulting in the formation of a semiconducting energy band gap, and the Fermi level resides at the top of the valence band maximum, indicating p-type carriers in a α-phase. 23 The electronic band structure of β-Ag 2 Te shows that the Fermi level is pinned near the conduction band minimum.…”

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Thermoelectric properties of p-type PbTe/Ag2Te bulk composites by extrinsic phase mixing

Lee

Rhyee

2015

AIP Advances

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We investigated the thermoelectric properties of PbTe/Ag2Te bulk composites, synthesized by hand milling, mixing, and hot press sintering. From x-ray diffraction and energy dispersive x-ray spectroscopy measurements, we observed Ag2Te phase separation in the PbTe matrix without Ag atom diffusion. In comparison with previously reported pseudo-binary (PbTe)1−x(Ag2Te)x composites, synthesized by high temperature phase separation, the PbTe/Ag2Te bulk composites fabricated with a low temperature phase mixing process give rise to p-type conduction of carriers with significantly decreased electrical conductivity. This indicates that Ag atom diffusion in the PbTe matrix changes the sign of the Seebeck coefficient to n-type and also increases the carrier concentration. Effective p-type doping with low temperature phase separation by mixing and hot press sintering can enhance the thermoelectric performance of PbTe/Ag2Te bulk composites, which can be used as a p-type counterpart of n-type (PbTe)1−x(Ag2Te)x bulk composites.

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“…It is found in the papers [4,5] that dispersion law for electrons conforms to the Kane model, in this case electron concentration is determined in the following way:…”

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Resonance Scattering of Electrons in Ag₂Te

et al. 2011

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The temperature dependences of electric conductivity σ, the Hall coefficient R of p-Ag 2 Te in 4.2-200 K temperature interval for acceptor concentration N a ≤ 6 × 10 16 cm −3 were investigated. The minimum σ(T ) was observed for all samples in ≈ 50 ÷ 80 K temperature interval. It was observed that the depth of minimum is increased with N a decrease. It was shown that the part resonance scattering of electrons in minimum of σ(T ) and maximum of |α n (T )| region is 16-18%.

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Electrical and thermoelectric properties of p-Ag2Te in the β phase

Cited by 16 publications

References 1 publication

High Thermoelectric Performance in PbTe Due to Large Nanoscale Ag2Te Precipitates and La Doping

High Thermoelectric Performance in PbTe Due to Large Nanoscale Ag2Te Precipitates and La Doping

Thermoelectric properties of p-type PbTe/Ag2Te bulk composites by extrinsic phase mixing

Resonance Scattering of Electrons in Ag₂Te

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Electrical and thermoelectric properties of p-Ag2Te in the β phase

Cited by 16 publications

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High Thermoelectric Performance in PbTe Due to Large Nanoscale Ag2Te Precipitates and La Doping

High Thermoelectric Performance in PbTe Due to Large Nanoscale Ag2Te Precipitates and La Doping

Thermoelectric properties of p-type PbTe/Ag2Te bulk composites by extrinsic phase mixing

Resonance Scattering of Electrons in Ag2Te

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Resonance Scattering of Electrons in Ag₂Te