Dynamic doping and Cottrell atmosphere optimize the thermoelectric performance of n-type PbTe

High thermoelectric energy conversion efficiency requires a large figure-of-merit, zT, over a broad temperature range. To achieve this, we optimize the carrier concentrations of n-type PbTe from room up to hot-end temperatures by co-doping Bi and Ag. Bi is an efficient n-type dopant in PbTe, often leading to excessive carrier concentration at room temperature. As revealed by density functional theory calculations, the formation of Bi and Ag defect complexes is exploited to optimize the room temperature carrier concentration. At elevated temperatures, we demonstrate the dynamic dissolution of Ag2Te precipitates in PbTe in situ by heating in a scanning transmission electron microscope. The release of n-type Ag interstitials with increasing temperature fulfills the requirement of higher carrier concentrations at the hot end. Moreover, as characterized by atom probe tomography, Ag atoms aggregate along parallel dislocation arrays to form Cottrell atmospheres. This results in enhanced phonon scattering and leads to a low lattice thermal conductivity. As a result of the synergy of dynamic doping and phonon scattering at decorated dislocations, an average zT of 1.0 is achieved in n-type Bi/Ag-codoped PbTe between 400 and 825 K. Introducing dopants with temperature-dependent solubility and strong interaction with dislocation cores enables simultaneous optimization of the average power factor and thermal conductivity, providing a new concept to exploit in the field of thermoelectrics

Exceptionally low thermal conductivity realized in the chalcopyrite CuFeS2 via atomic-level lattice engineering

© 2022 Elsevier LtdDesigning irregular but desirable atomic arrangements in crystal lattices of solids can greatly change their intrinsic physical properties beyond expectations from common doping and alloying. However, structures of solids are generally determined by thermodynamic preferences during solid-state reactions, strictly restricting delicate atomic-level lattice engineering. Here, we report a new strategy of realizing desirable defect architecture in a highly predictable way to control thermal and charge transport properties of solids. Introducing unusually high concentration indium to the tetragonal chalcopyrite CuFeS2 to form the Cu1−xInxFeS2 (x = 0–0.12) system stabilizes the highly unusual local structure, namely, high-temperature polymorph of cubic zinc blende structure in the surrounding matrix and displaced In+ cation with 5s2 lone pair electrons from the Cu+ sublattice. This substantially suppresses notoriously high lattice thermal conductivity of tetrahedrally networked CuFeS2 to record-low values ~0.79 W m−1 K−1 at 723 K through multiscale scattering and softening mechanisms of heat-carrying phonon, approaching its theoretical lower limit. Consequently, one of the highest thermoelectric figures of merit, ZT, among chalcopyrite sulfides is achieved. Our design principle utilizes standard potentials and ionic radius of constituent elements, thereby readily applicable to designing various classes of solids. Remarkably, we directly imaged the atomic-level structure of positional disorder stabilizing the high-temperature phase and off-centered In+ from the ideal position employing a scanning transmission electron microscope. This observation shows how our material design strategy works, and provides important understanding for how local structures in solids form when either compatible or incompatible atoms are introduced to the crystal lattices.11Nsciescopu

High‐Performance Industrial‐Grade CsPbBr3 Single Crystal by Solid–Liquid Interface Engineering

Abstract All‐inorganic metal halide perovskite CsPbBr3 crystal is regarded as an attractive alternative to high purity Ge and CdZnTe for room temperature γ‐ray detection. However, high γ‐ray resolution is only observable in small CsPbBr3 crystal; more practical and deployable large crystal exhibits very low, and even no detection efficiency, thereby thwarting prospects for cost‐effective room temperature γ‐ray detection. The poor performance of large crystal is attributed to the unexpected secondary phase inclusion during crystal growth, which traps the generated carriers. Here, the solid–liquid interface during crystal growth is engineered by optimizing the temperature gradient and growth velocity. This minimizes the unfavorable formation of the secondary phase, leading to industrial‐grade crystals with a diameter of 30 mm. This excellent‐quality crystal exhibits remarkably high carrier mobility of 35.4 cm2 V−1 s−1 and resolves the peak of 137Cs@ 662 keV γ‐ray at an energy resolution of 9.91%. These values are the highest among previously reported large crystals

Enhancing thermoelectric performance of Sb2Te3 through swapped bilayer defects

Lattice defects are typically used to tailor the thermoelectric properties of materials. It is desirable that such defects improve the electrical conductivity, while, at the same time, reduce the thermal conductivity, for an overall improvement on the thermoelectric properties of materials. Here, we report on an extended defect in Sb2Te3 consisting of swapped bilayers with chemical intermixing of Sb and Te atoms, which can be generated and effectively manipulated in polycrystalline samples through synthetic methods and thermal treatments. The swapped bilayers bridge the spatial gaps between the Sb2Te3 quintuple-layer blocks, enhancing the charge carrier mobility and thus the electrical conductivity. These defects also result in a reduced lattice thermal conductivity through suppressing phonon transport. These synergistic effects contribute together to an improved thermoelectric quality factor and an enhanced figure of merit (zT) value in Sb2Te3

Atomic Level Defect Structure Engineering for Unusually High Average Thermoelectric Figure of Merit in n-Type PbSe Rivalling PbTe

Realizing high average thermoelectric figure of merit (ZT(ave)) and power factor (PFave) has been the utmost task in thermoelectrics. Here the new strategy to independently improve constituent factors in ZT is reported, giving exceptionally high ZT(ave) and PFave in n-type PbSe. The nonstoichiometric, alloyed composition and resulting defect structures in new Pb1+xSe0.8Te0.2 (x = 0-0.125) system is key to this achievement. First, incorporating excess Pb unusually increases carrier mobility (mu(H)) and concentration (n(H)) simultaneously in contrast to the general physics rule, thereby raising electrical conductivity (sigma). Second, modifying charge scattering mechanism by the authors' synthesis process boosts a magnitude of Seebeck coefficient (S) above theoretical expectations. Detouring the innate inverse proportionality between n(H) and mu(H); and sigma and S enables independent control over them and change the typical trend of PF to temperature, giving remarkably high PFave approximate to 20 mu W cm(-1) K-2 from 300 to 823 K. The dual incorporation of Te and excess Pb generates unusual antisite Pb at the anionic site and displaced Pb from the ideal position, consequently suppressing lattice thermal conductivity. The best composition exhibits a ZT(ave) of approximate to 1.2 from 400 to 823 K, one of the highest reported for all n-type PbQ (Q = chalcogens) materials.11Nsciescopu

Exceptionally High Average Power Factor and Thermoelectric Figure of Merit in n-type PbSe by the Dual Incorporation of Cu and Te

© 2020 American Chemical Society. Thermoelectric materials with high average power factor and thermoelectric figure of merit (ZT) has been a sought-after goal. Here, we report new n-type thermoelectric system CuxPbSe0.99Te0.01 (x = 0.0025, 0.004, and 0.005) exhibiting record-high average ZT similar to 1.3 over 400-773 K ever reported for n-type polycrystalline materials including the state-of-the-art PbTe. We concurrently alloy Te to the PbSe lattice and introduce excess Cu to its interstitial voids. Their resulting strong attraction facilitates charge transfer from Cu atoms to the crystal matrix significantly. It follows the increased carrier concentration without damaging its mobility and the consequently improved electrical conductivity. This interaction also increases effective mass of electron in the conduction band according to DFT calculations, thereby raising the magnitude of Seebeck coefficient without diminishing electrical conductivity. Resultantly, Cu0.005PbSe0.99Te0.01 attains an exceptionally high average power factor of similar to 27 mu W cm(-1) K-2 from 400 to 773 K with a maximum of similar to 30 mu W cm(-1) K-2 at 300 K, the highest among all n- and p-type PbSe-based materials. Its similar to 23 mu W cm(-1) K-2 at 773 K is even higher than similar to 21 mu W Cal(-1) K-2 of the state-of-the-art n-type PbTe. Interstitial Cu atoms induce the formation of coherent nanostructures. They are highly mobile, displacing Pb atoms from the ideal octahedral center and severely distorting the local microstructure. This significantly depresses lattice thermal conductivity to -0.2 Wm(-1) K-1 at 773 K below the theoretical lower bound. The multiple effects of the dual incorporation of Cu and Te synergistically boosts a ZT of Cu0.005PbSe0.99Te0.01 to similar to 1.7 at 773 K11sciescopu

Engineering an atomic-level crystal lattice and electronic band structure for an extraordinarily high average thermoelectric figure of merit in n-type PbSe

We stabilize multiscale defect structures involving interstitial Cu, displaced Pb and Se atoms from the regular lattice points, dislocations prompted by scarce anion vacancies, and nanoscale mosaics driven thermodynamically by the new composition CuxPb(Se0.8Te0.2)(0.95) (x = 0-0.0057). Directly observing their atomic-resolution structures, employing a spherical aberration-corrected scanning transmission electron microscope and atom probe tomography, uncovers formation mechanisms, helping understand how they affect bulk transport properties. They independently manipulate the physical quantities determining the thermoelectric figure of merit, ZT. Carrier concentration dynamically boosts electrical conductivity with rising temperature while negligibly damaging carrier mobility. The significantly increased effective mass of electrons in the conduction band above the theoretical prediction gives a high magnitude of Seebeck coefficients. Consequently, the best composition achieves a remarkably high average power factor of & SIM;24 & mu;W cm(-1) K-2 from 300 to 823 K, with a substantially depressed lattice thermal conductivity of & SIM;0.2 W m(-1) K-1 at 723 K. With a ZT of & SIM;0.55 at 300 K, an average ZT is & SIM;1.30 from 400 to 823 K, the highest for all n-type polycrystalline thermoelectric systems including PbTe-based materials. The achievement in this work greatly escalates the predictability in designing defect structures for high thermoelectric performance, and demonstrates that PbSe can eventually outperform PbTe in thermoelectrics.11Nsciescopu

Exceptionally High Average Power Factor and Thermoelectric Figure of Merit in ntype PbSe by the Dual Incorporation of Cu and Te

© 2020 American Chemical Society. Thermoelectric materials with high average power factor and thermoelectric figure of merit (ZT) has been a sought-after goal. Here, we report new n-type thermoelectric system CuxPbSe0.99Te0.01 (x = 0.0025, 0.004, and 0.005) exhibiting record-high average ZT similar to 1.3 over 400-773 K ever reported for n-type polycrystalline materials including the state-of-the-art PbTe. We concurrently alloy Te to the PbSe lattice and introduce excess Cu to its interstitial voids. Their resulting strong attraction facilitates charge transfer from Cu atoms to the crystal matrix significantly. It follows the increased carrier concentration without damaging its mobility and the consequently improved electrical conductivity. This interaction also increases effective mass of electron in the conduction band according to DFT calculations, thereby raising the magnitude of Seebeck coefficient without diminishing electrical conductivity. Resultantly, Cu0.005PbSe0.99Te0.01 attains an exceptionally high average power factor of similar to 27 mu W cm(-1) K-2 from 400 to 773 K with a maximum of similar to 30 mu W cm(-1) K-2 at 300 K, the highest among all n- and p-type PbSe-based materials. Its similar to 23 mu W cm(-1) K-2 at 773 K is even higher than similar to 21 mu W Cal(-1) K-2 of the state-of-the-art n-type PbTe. Interstitial Cu atoms induce the formation of coherent nanostructures. They are highly mobile, displacing Pb atoms from the ideal octahedral center and severely distorting the local microstructure. This significantly depresses lattice thermal conductivity to -0.2 Wm(-1) K-1 at 773 K below the theoretical lower bound. The multiple effects of the dual incorporation of Cu and Te synergistically boosts a ZT of Cu0.005PbSe0.99Te0.01 to similar to 1.7 at 773 K11sciescopu

Bulk Metamaterials Exhibiting Chemically Tunable Hyperbolic Responses

© 2021 American Chemical Society.Extraordinary properties of traditional hyperbolic metamaterials, not found in nature, arise from their man-made subwavelength structures causing unique light-matter interactions. However, their preparation requiring nanofabrication processes is highly challenging and merely provides nanoscale two-dimensional structures. Stabilizing their bulk forms via scalable procedures has been a sought-goal for broad applications of this technology. Herein, we report a new strategy of designing and realizing bulk metamaterials with finely tunable hyperbolic responses. We develop a facile two-step process: (1) self-assembly to obtain heterostructured nanohybrids of building blocks and (2) consolidation to convert nanohybrid powders to dense bulk pellets. Our samples have centimeter-scale dimensions typically, readily further scalable. Importantly, the thickness of building blocks and their relative concentration in bulk materials serve as a delicate means of controlling hyperbolic responses. The resulting new bulk heterostructured material system consists of the alternating h-BN and graphite/graphene nanolayers and exhibits significant modulation in both type-I and type-II hyperbolic resonance modes. It is the first example of real bulk hyperbolic metamaterials, consequently displaying the capability of tuning their responses along both in-plane and out-of-plane directions of the materials for the first time. It also distinctly interacts with unpolarized and polarized transverse magnetic and electronic beams to give unique hyperbolic responses. Our achievement can be a new platform to create various bulk metamaterials without complicated nanofabrication techniques. Our facile synthesis method using common laboratory techniques can open doors to broad-range researchers for active interdisciplinary studies for this otherwise hardly accessible technology.11Nsciescopu