Role of Nanostructuring and Microstructuring in Silver Antimony Telluride Compounds for Thermoelectric Applications

Cojocaru‐Mirédin, Oana; Abdellaoui, Lamya; Nagli, Michael; Zhang, Siyuan; Yu, Yuan; Scheu, Christina; Raabe, Dierk; Wuttig, Matthias; Amouyal, Yaron

doi:10.1021/acsami.7b00689

Cited by 32 publications

(30 citation statements)

References 73 publications

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“…APT is indeed a remarkable method for 3D atomistic distribution analysis that determines the composition at the nanoscale and allows for the identification of NPs. [ 20,21 ] Hence, the present work enables a better understanding of the nature of the NPs in TAGS‐ x thin‐film thermoelectric chalcogenides, which further confirms the role of nanostructures for the thermoelectric performance. Thin‐film thermoelectrics are indeed very relevant for cooling application [ 22 ] and for power generation.…”

Section: Introductionsupporting

confidence: 70%

Employing Interfaces with Metavalently Bonded Materials for Phonon Scattering and Control of the Thermal Conductivity in TAGS‐x Thermoelectric Materials

Rodenkirchen

Cagnoni

Jakobs

et al. 2020

Adv Funct Materials

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The thermoelectric compound (GeTe) x (AgSbTe 2 ) 1−x , in short (TAGS-x), is investigated with a focus on two stoichiometries, i.e., TAGS-50 and TAGS-85. TAGS-85 is currently one of the most studied thermoelectric materials with great potential for thermoelectric applications. Yet, surprisingly, the lowest thermal conductivity is measured for TAGS-50, instead of TAGS-85. To explain this unexpected observation, atom probe tomography (APT) measurements are conducted on both samples, revealing clusters of various compositions and sizes. The most important role is attributed to Ag 2 Te nanoprecipitates (NPs) found in TAGS-50. In contrast to the Ag 2 Te NPs, the matrix reveals an unconventional bond breaking mechanism. More specifically, a high probability of multiple events (PME) of ≈60% is observed for the matrix by APT. Surprisingly, the PME value decreases abruptly to ≈20-30% for the Ag 2 Te NPs. These differences can be attributed to differences in chemical bonding. The precipitates' PME value is indicative of normal bonding, i.e., covalent bonding with normal optical modes, while materials with this unconventional bond breaking found in the matrix are characterized by metavalent bonding. This implies that the interface between the metavalently bonded matrix and covalently bonded Ag 2 Te NP is partly responsible for the reduced thermal conductivity in TAGS-50.

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Section: Introductionsupporting

confidence: 70%

Employing Interfaces with Metavalently Bonded Materials for Phonon Scattering and Control of the Thermal Conductivity in TAGS‐x Thermoelectric Materials

Rodenkirchen

Cagnoni

Jakobs

et al. 2020

Adv Funct Materials

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“…Conversely, κ l -values increase from 6 h aging up to 48 h aging, which seems to deviate from the trend introduced before. This is explained by the role of the degree of matrix supersaturation in scattering phonons, as utilized by us previously [28,37]. The as-quenched sample comprises non-equilibrium, strained, and super-saturated PbTe solid solution that relaxes upon aging.…”

Section: Electronic Transport Propertiesmentioning

confidence: 99%

Microstructure Evolution of Ag-Alloyed PbTe-Based Compounds and Implications for Thermoelectric Performance

et al. 2017

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Abstract:We investigate the microstructure evolution of Ag-alloyed PbTe compounds for thermoelectric (TE) applications with or without additions of 0.04 at. % Bi. We control the nucleation and temporal evolution of Ag 2 Te-precipitates in the PbTe-matrix applying designated aging heat treatments, aiming to achieve homogeneous dispersion of precipitates with high number density values, hypothesizing that they act as phonon scattering centers, thereby reducing lattice thermal conductivity. We measure the temperature dependence of the Seebeck coefficient and electrical and thermal conductivities, and correlate them with the microstructure. It is found that lattice thermal conductivity of PbTe-based compounds is reduced by controlled nucleation of Ag 2 Te-precipitates, exhibiting a number density value as high as 2.7 × 10 20 m −3 upon 6 h aging at 380 • C. This yields a TE figure of merit value of ca. 1.4 at 450 • C, which is one on the largest values reported for n-type PbTe compounds. Subsequent aging leads to precipitate coarsening and deterioration of TE performance. Interestingly, we find that Bi-alloying improves the alloys' thermal stability by suppressing microstructure evolution, besides the role of Bi-atoms as electron donors, thereby maintaining high TE performance that is stable at elevated service temperatures. The latter has prime technological significance for TE energy conversion.

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“…Hence the atomic structure and the resulting properties in these distinct areas must be explored in detail, too. Adequate tools are transmission electron microscopy (TEM) [13], atom probe tomography [14,15], and scanning probe microscopy [16,17]. Among these, scanning tunneling microscopy (STM) and spectroscopy (STS) provide the advantage that the electronic density of states (DOS) close to the Fermi level E F is probed simultaneously, down to the atomic length scale with submeV resolution [18,19].…”

Section: Introductionmentioning

confidence: 99%

Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5

et al. 2017

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Scanning tunneling microscopy (STM) and spectroscopy (STS) in combination with density functional theory (DFT) calculations are employed to study the surface and subsurface properties of the metastable phase of the phase-change material Ge 2 Sb 2 Te 5 as grown by molecular beam epitaxy. The (111) surface is covered by an intact Te layer, which nevertheless permits the detection of the more disordered subsurface layer made of Ge and Sb atoms. Centrally, we find that the subsurface layer is significantly more ordered than expected for metastable Ge 2 Sb 2 Te 5 . First, we show that vacancies are nearly absent within the subsurface layer. Secondly, the potential fluctuation, tracked by the spatial variation of the valence band onset, is significantly less than expected for a random distribution of atoms and vacancies in the subsurface layer. The strength of the fluctuation is compatible with the potential distribution of charged acceptors without being influenced by other types of defects. Thirdly, DFT calculations predict a partially tetrahedral Ge bonding within a disordered subsurface layer, exhibiting a clear fingerprint in the local density of states as a peak close to the conduction band onset. This peak is absent in the STS data implying the absence of tetrahedral Ge, which is likely due to the missing vacancies required for structural relaxation around the shorter tetrahedral Ge bonds. Finally, isolated defect configurations with a low density of 10 −4 nm −2 are identified by comparison of STM and DFT data, which corroborates the significantly improved order in the epitaxial films driven by the buildup of vacancy layers.

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Role of Nanostructuring and Microstructuring in Silver Antimony Telluride Compounds for Thermoelectric Applications

Cited by 32 publications

References 73 publications

Employing Interfaces with Metavalently Bonded Materials for Phonon Scattering and Control of the Thermal Conductivity in TAGS‐x Thermoelectric Materials

Employing Interfaces with Metavalently Bonded Materials for Phonon Scattering and Control of the Thermal Conductivity in TAGS‐x Thermoelectric Materials

Microstructure Evolution of Ag-Alloyed PbTe-Based Compounds and Implications for Thermoelectric Performance

Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5

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