81 research outputs found
High-performance thermoelectric energy conversion: A tale of atomic ordering in AgSbTe2
No full textThe highly enhanced thermoelectric figure of merit, zT ≈ 2.6 at 573 K, obtained recently in Cd-doped polycrystalline AgSbTe2 by Roychowdhury et al. ( Science 2021, 371, 722) brings it to the forefront of thermoelectric and energy materials research. Ag/Sb cationic ordering in polycrystalline AgSbTe2 was a challenging issue for a long time: their ordered arrangement in the cationic sublattice in polycrystalline samples remained elusive despite multiple theoretical predictions and experimental studies. Recently, selective cation doping has been used to enhance the Ag/Sb ordering, and cation ordered nanoscale (2–4 nm) domains were observed in polycrystalline AgSbTe2, which reduce lattice thermal conductivity. The enhanced cation ordering also delocalizes disorder-induced localized electronic states, and consequently the electronic transport enhances. In this Focus Review, we provide the details of the rational design of a high-performance thermoelectric material using the recently developed atomic order–disorder optimization strategy with AgSbTe2 as an example. Atomic disorder is ubiquitous in most thermoelectric materials, and the atomic order–disorder optimization strategy applies to a large variety of thermoelectric materials
Slight Symmetry Reduction in Thermoelectrics
No full textThermoelectric research on germanium telluride (GeTe) has been mainly focused on the enhancement of its performance in the high-temperature cubic phase since the 1960s. Recently in Joule, Pei and co-workers achieved an unprecedented thermoelectric figure of merit in rhombohedral-phase GeTe by exploiting slight symmetry breaking in the structure, which simultaneously improved the electronic properties and reduced the lattice thermal conductivity
Effect of In and Cd co-doping on the thermoelectric properties of Sn1−xPbxTe
No full textPristine tin telluride (SnTe) with a similar electronic structure to PbTe shows inferior thermoelectric performance owing to high p-type hole concentration (1021 cm−3), high lattice thermal conductivity, κlatt (∼2.8 W mK−1 at room temperature) and large energy gap between light and heavy hole valence bands. Interestingly, 30 mol% substitution of lead in SnTe decreases the excess hole carrier concentration and lattice thermal conductivity (∼0.67 W m−1K−1 at 300 K) significantly. Here, we report the promising thermoelectric performance in Sn0.70Pb0.30Te by enhancing the Seebeck coefficient via the co-adjuvant effect of resonant level formation and valence band convergence. We obtain a Seebeck coefficient value of ∼141 μV K−1 at 300 K, which further increases to ∼260 μV K−1 at 708 K for Sn0.70Pb0.30Te—3% Cd and 0.50% In sample. This is one of the highest S values for SnTe based system, to the best of our knowledge. In and Cd have discrete but complementary roles to augment the Seebeck coefficient value of Sn0.70Pb0.30Te where In acts as a resonant dopant and Cd serves as valence band convergent, respectively, as demonstrated by the well-known Pisarenko plot of SnTe. Finally, we have achieved a maximum thermoelectric figure of merit, zT, of ∼0.82 at 654 K for Sn0.70Pb0.30Te—3% Cd and 0.25% In sample
The journey of tin chalcogenides towards high-performance thermoelectrics and topological materials
No full textSn-Chalcogenides are recognized as high performance thermoelectrics and topological insulators due to their unique crystal and electronic structures and lattice dynamics.</p
FIGURE 5 in A new species of Cephalaeschna Selys, 1883 (Odonata: Anisoptera: Aeshnidae) from Neora Valley National Park, West Bengal, India, with notes on C. acanthifrons Joshi & Kunte, 2017 and C. viridifrons (Fraser, 1922)
No full textFIGURE 5: A. Cephalaeschna acanthifrons holotype from Arunachal Pradesh, thorax [Photo by Subhajit Mazumder]; B. Cephalaeschna viridifrons from Neora Valley National Park, West Bengal, India [Photo by the author]; C. C. acanthifrons, face [Photo by Subhajit Mazumder]; D. C. viridifrons from Neora Valley National Park, face [Photo by the author]; E. C. viridifrons from Neora Valley National Park, abdomen dorsal view [Photo by the author]; F. C. acanthifrons holotype, anal appendages [Photo by Shantanu Joshi, NCBS]; G. C. viridifrons from Assam, anal appendages (reproduced from Asahina 1981a); H. C. viridifrons from Nepal, anal appendages (reproduced from Asahina 1981a); I. C. viridifrons from Neora Valley National Park, anal appendages [Photo by the author].Published as part of Dawn, Prosenjit, 2021, A new species of Cephalaeschna Selys, 1883 (Odonata: Anisoptera: Aeshnidae) from Neora Valley National Park, West Bengal, India, with notes on C. acanthifrons Joshi & Kunte, 2017 and C. viridifrons (Fraser, 1922), pp. 371-380 in Zootaxa 4949 (2) on page 378, DOI: 10.11646/zootaxa.4949.2.10, http://zenodo.org/record/463619
Enhanced thermoelectric performance in topological crystalline insulator n-type Pb0.6Sn0.4Te by simultaneous tuning of the band gap and chemical potential
No full textTailoring the electronic structure of topological crystalline insulators (TCIs) is necessary to enhance their thermoelectric (TE) performance. p-Type chemical doping in a TCI such as Pb0.6Sn0.4Te exhibited a significantly high TE figure of merit (zT), but the n-type Pb0.6Sn0.4Te is still elusive and is urgently needed for thermoelectric applications. Herein, we report enhanced thermoelectric performance in n-type iodine (I) doped Pb0.6Sn0.4Te. Aliovalent I− doping in the Te2− sublattice of Pb0.6Sn0.4Te widens the band gap via breaking of local crystal mirror symmetry, which decreases the bipolar conduction and pushes the Seebeck maxima towards high temperatures. Iodine doping in Pb0.6Sn0.4Te significantly increases the n-type carrier concentration and shifts the chemical potential (Fermi level) inside the conduction band of Pb0.6Sn0.4Te, thus improving the electrical transport properties. We report a maximum zT of 1.05 in the n-type Pb0.60Sn0.40Te0.995I0.005 sample at 620 K, which is 483% higher than pristine Pb0.6Sn0.4Te
High performance thermoelectric materials and devices based on GeTe
No full textThermoelectric materials have received recent attention due to their ability to convert waste heat to electrical energy directly and reversibly. Inorganic materials, especially Bi2Te3, PbTe and Si–Ge based alloys, have been investigated in the temperature range of 300–1000 K, among which PbTe based materials have been extensively studied, and reported to be the leading thermoelectric materials for mid-temperature power generation. However, environmental concern limits their large scale production due to the toxic nature of Pb. As an alternative, GeTe-rich alloys such as TAGS (GeTe–AgSbTe2) have been largely investigated since the 1960s. Most recently, some of the new materials in the GeTe family have been introduced such as Ge0.87Pb0.13Te, the homologous series of Sb2Te3(GeTe)n and Ge0.9Sb0.1Te, and are reported to exhibit high thermoelectric performance, inherently formed nano and microstructure modulations, and high thermal and mechanical stability. These collective enhanced properties of GeTe-rich alloys have generated great interest in investigating further new GeTe based alloys for intermediate temperature thermoelectric applications. In order to provide the fundamental understanding, technological insights, and to further promote the GeTe based alloys, we hereby present a review on (i) the crystal structure, nano/microstructure, phase transition, electronic structure, and thermoelectric properties of GeTe, (ii) correlation of compositional and microstructure modulations and thermoelectric properties of doped GeTe, TAGS based alloys, Ge–Pb–Te materials, and Ge–Sb–Te materials, (iii) mechanical properties, (iv) past and present devices based on GeTe materials and (v) future directions
Reduction of thermal conductivity through nanostructuring enhances the thermoelectric figure of merit in Ge1−xBixTe
No full textA promising thermoelectric figure of merit, zT, of ∼1.3 at 725 K was obtained in high quality crystalline ingots of Ge1−xBixTe. The substitution of Bi3+ in a Ge2+ sublattice of GeTe significantly reduces the excess hole concentration due to the aliovalent donor dopant nature of Bi3+. Reduction in carrier density optimizes electrical conductivity, and subsequently enhances the Seebeck coefficient in Ge1−xBixTe. More importantly, a low lattice thermal conductivity of ∼1.1 W m−1 K−1 for Ge0.90Bi0.10Te was achieved, which is due to the collective phonon scattering from meso-structured grain boundaries, nano-structured precipitates, nano-scale defect layers, and solid solution point defects. We have obtained a reasonably high mechanical stability for the Ge1−xBixTe samples. The measured Vickers microhardness value of the high performance sample is ∼165 HV, which is comparatively higher than that of state-of-the-art thermoelectric materials, such as PbTe, Bi2Te3, and Cu2Se
Observation of chiral surface state in superconducting NbGe2
No full textPublisher Copyright: © 2025 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by Max Planck Society.The interplay between topology and superconductivity in quantum materials presents opportunities for exploring novel quantum phenomena. In this study, we investigate the topological properties and superconductivity of the nonsymmorphic chiral superconductor NbGe2 using high-resolution angle-resolved photoemission spectroscopy (ARPES), transport measurements, and ab initio calculations. The ARPES data revealed exotic chiral surface states on the (100) surface originating from the inherent chiral crystal structure. Our ab initio calculations suggest that NbGe2's electronic structure may include elusive Weyl fermions, highlighting its potential for topological superconductivity. Furthermore, we uncovered the signatures of van Hove singularities, which may enhance many-body interactions. Additionally, transport measurements demonstrated that NbGe2 exhibits superconductivity below 2K. Overall, our comprehensive results provide strong experimental evidence that NbGe2 is a promising platform for investigating the interplay between nontrivial band topology, possible Weyl fermions, vHSs, and superconductivity in chiral quantum materials.Peer reviewe
Effect of potassium doping on electronic structure and thermoelectric properties of topological crystalline insulator
No full textTopological crystalline insulator (TCI), Pb0.6Sn0.4Te, exhibits metallic surface states protected by crystal mirror symmetry with negligibly small band gap. Enhancement of its thermoelectric performances needs tuning of its electronic structure particularly through engineering of its band gap. While physical perturbations tune the electronic structure of TCI by breaking of the crystal mirror symmetry, chemical means such as doping have been more attractive recently as they result in better thermoelectric performance in TCIs. Here, we demonstrate that K doping in TCI, Pb0.6Sn0.4Te, breaks the crystal mirror symmetry locally and widens electronic band gap, which is confirmed by direct electronic absorption spectroscopy and electronic structure calculations. K doping in Pb0.6Sn0.4Te increases p-type carrier concentration and suppresses the bipolar conduction via widening a band gap, which collectively boosts the thermoelectric figure of merit (ZT) to 1 at 708 K
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