High-efficiency thermoelectric materials require simultaneously high power factors and low thermal conductivities. Aligning band extrema to achieve high band degeneracy, as realized in PbTe, is one ...of the most efficient approaches to enhance power factor. However, this approach usually relies on band structure engineering, e.g., via chemical doping or strain. By employing first-principles methods with explicit computation of phonon and carrier lifetimes, here we show two full-Heusler compounds Li
TlBi and Li
InBi have exceptionally high power factors and low lattice thermal conductivities at room temperature. The expanded rock-salt sublattice of these compounds shifts the valence band maximum to the middle of the Σ line, increasing the band degeneracy by a factor of three. Meanwhile, resonant bonding in the PbTe-like sublattice and soft Tl-Bi (In-Bi) bonding interaction is responsible for intrinsic low lattice thermal conductivities. Our results present an alternative strategy of designing high performance thermoelectric materials.
Semiconducting half and, to a lesser extent, full Heusler compounds are promising thermoelectric materials due to their compelling electronic properties with large power factors. However, ...intrinsically high thermal conductivity resulting in a limited thermoelectric efficiency has so far impeded their widespread use in practical applications. Here, we report the computational discovery of a class of hitherto unknown stable semiconducting full Heusler compounds with ten valence electrons (X_{2}YZ, X=Ca, Sr, and Ba; Y=Au and Hg; Z=Sn, Pb, As, Sb, and Bi) through high-throughput ab initio screening. These new compounds exhibit ultralow lattice thermal conductivity κ_{L} close to the theoretical minimum due to strong anharmonic rattling of the heavy noble metals, while preserving high power factors, thus resulting in excellent phonon-glass electron-crystal materials.
The pursuit of thermoelectric materials poses a formidable challenge, given that numerous predicted candidates fail in real-world applications. An effective way to enhance the success rate of ...computer predictions is to focus on key elements shared by workable thermoelectrics. These elements include chalcogens (Q = S and Se), pentagons (III = &z.dbd;As, Sb, and Bi), coinage metals (I = &z.dbd;Cu, Ag, and Au), and post-transition metals (III/IV = &z.dbd;Ga, In, Ge, Sn, Pb). Here, we screen two types of coinage-based quaternary chalcogenides possessing these crucial thermoelectric elements: I-II-IV-Q
4
and I-II
2
-III-Q
4
. We found that the thermoelectric performance of these compounds originates from the unconventional I-Q bonding formed through strong coupling between the coinage d and chalcogen p orbitals. The d-p hybridization forms a filled antibonding state at the top of the valence band that not only weakens the I-Q bonds, which lowers the lattice thermal conductivity, but also generates a flat-and-dispersive and multi-valley degenerate valence band, resulting in a high p-type power factor. So, the higher the share of coinage metals and thus the I-Q bonding within the unit cell, the lower the lattice thermal conductivity is. Such soft I-Q bonds, when accompanied by breakage of local symmetry and corner-sharing tetrahedral units, suppress the lattice thermal conductivity down to the amorphous limit. For instance, Ag
2
PbGeS
4
demonstrates a lattice thermal conductivity of 0.15 W m
−1
K
−1
because of various anharmonic scattering processes caused by lone-pair-induced off-centering of Pb, weak Ag-Ag interactions, and disrupted corner-sharing networks, the combination that yields a
zT
exceeding two. Our findings highlight the potential of coinage-based quaternary chalcogenides as practical thermoelectric materials, paving the way for the development of customizable thermoelectrics.
The pursuit of thermoelectric materials poses a formidable challenge, given that numerous predicted candidates fail in real-world applications.
Using first-principles density functional theory (DFT), we calculate the diffusivities of 32 different solute elements—all transition metals, together with Al and Si—in fcc cobalt within the ...formalism of the five-frequency model. For self-diffusion in fcc cobalt, we compare the accuracy of various approximations to the exchange-correlation energy functional of DFT in estimating the activation energy, and find that only the Perdew-Burke-Ernzerhof (PBE) approximation agrees well with experimental reports and all other functionals largely overestimate it. Our calculations also show that an accurate estimation of the self-diffusion coefficient requires explicit calculation of the effective jump frequency and vacancy formation entropy via phonons. Using accurate self-diffusion data and scaling all solute-related attempt frequencies with respect to the attempt frequency for self-diffusion using a simple relation involving the atomic mass and melting temperature of the solute yields solute diffusivities in excellent agreement with experiments, where such data is available. We find that large solutes spontaneously relax toward the nearest neighbor vacancy to relieve the misfit strain, and the extent of this relaxation correlates negatively with the migration energy. Thus, in general, larger solutes have lower migration energies and diffuse faster than smaller solutes in fcc cobalt. However, extremely large solutes, e.g., group III elements Sc, Y, Lu, tend to be trapped in an energy valley located halfway toward the vacancy, and monovacancy mediated diffusion may no longer be valid in such cases. Finally, for all the solutes considered, we systematically tabulate the diffusion-related quantities calculated—diffusion prefactors, migration and activation energies—constructing an extensive and accurate first-principles database for solute diffusion in fcc cobalt.
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The search for new thermoelectric materials that directly convert (waste) heat into electricity is a high-cost and time-consuming experimental effort. To facilitate this process, we perform a ...systematic screening for synthesizable and stable ABQ 3 (A and B are metals; Q = S, Se) compounds using first-principles density functional theory calculations. A total of 40 ABQ 3 compounds are predicted to be highly competent thermoelectric materials with nontoxic and earth-abundant advantages. The calculated power factors of some of them (e.g., n-type SnHfS3, p-type SbGaS3, n-type PbHfS3, and so forth) are comparable (even outperform) those of the well-known thermoelectric materials such as PbTe and Bi2Te3. The detailed analysis of electronic band structure reveals that either one or a combination of “pudding-mold” type band structure, high valley degeneracy, and high orbital degeneracy is responsible for the high PF computed in this family of materials. Taking two representative cases, we validate a low lattice thermal conductivity in ABQ 3 compounds by calculating the Boltzmann transport equation using the highly accurate anharmonic lattice dynamics methods. Third-order interatomic force constants reveal that the anharmonicity and soft phonon modes, rooted in the nature of unconventional chemical bonds between the B-site metals and chalcogen atoms, lead to an ultralow lattice thermal conductivity in this family of materials. The combination of intrinsically low lattice thermal conductivity and high power factor has realized highly efficient n-type and p-type ABQ 3 thermoelectric materials showing various anisotropic characteristics. Considering the thermal and moisture stability of chalcogenide perovskites, our results suggest that this unexplored family of materials is a host of highly efficient and practical thermoelectric materials awaiting further experimental validation.
Research interest in chemical gas detection has been directed towards developing highly selective bio-inspired and eco-friendly materials that allow the integration of sensors in daily human life, ...such as the Internet of Things (IoT). In this regard, chemical sensors for detecting air pollutants are urgently needed for environmental safety. For instance, acute exposure to the colorless nitrogen oxide (NO)-as an anthropogenic gas-causes several diseases such as methemoglobinemia, emphysema, and bronchiolitis, to name just three. In the present work, to find materials for sensing the dilute amount of NO, we use the density functional non-equilibrium Green's function formalism to thoroughly screen the bio-inspired metalloporphyrin (MPor) based junctions. The detailed analysis of adsorption energy, sensitivity, recovery time, and selectivity reveals that the nature of the central M, mainly its orbitals' energy ordering, affects the overall performance of MPors for sensor applications. We find that the the CrPor-based device is sensitive ( 0.85%) and also selective, in comparison with other pollutants like CO and CO
2
, toward NO detection. The contaminated sensor then can be recovered within 0.25 s at a small bias voltage of 0.5 V. The bio-inspired CrPor molecules are thus promising materials for designing superior NO nanoscale chemical sensors. Our computational approach provides a basis for the future optimization and development of gas nanosensors awaiting further experimental validations.
Chromium Porphyrin-based sensor under a small bias voltage achieves both high sensitivity and selectivity for sensing an extremely dilute amount of NO.
The development of cost-effective and eco-friendly sensor materials is needed to realize the application of detectors in daily life-such as in the internet of things. In this regard, monitoring air ...pollutants such as carbon monoxide (CO) and carbon dioxide (CO
), mainly emitted by anthropogenic sources from daily human activities, is of great importance. In particular, developing a susceptible and portable CO
sensor raises a dilemma because of the chemical inertness and non-polarity of CO
molecules. We find that porphyrin-based materials, exploited by nature in biological systems, are a playground to search for such sensor materials. Using density functional non-equilibrium Green's function formalism, we fully screen all 3d metalloporphyrin (MPor) based devices to find efficient CO and CO
gas sensors. Our detailed analysis of the adsorption energy, molecular orbitals, transmission spectra, sensitivity, and recovery time reveals that the nature of central M alters the efficiency of MPor gas detectors. We find that CO and CO
can be monitored using, respectively, CoPor- and TiPor-based devices. The estimated sensitivity is around 100%, along with a fast recovery time at very low bias voltages (
≥ 0.5 V), which turn metalloporphyrins into promising candidates for the widespread development of enhanced CO and CO
sensors awaiting further experimental validations.
The synthesis of materials in high-pressure experiments has recently attracted increasing attention, especially since the discovery of record breaking superconducting temperatures in the ...sulfur-hydrogen and other hydrogen-rich systems. Commonly, the initial precursor in a high pressure experiment contains constituent elements that are known to form compounds at ambient conditions, however the discovery of high-pressure phases in systems immiscible under ambient conditions poses an additional materials design challenge. We performed an extensive multi component
ab initio
structural search in the immiscible Fe-Bi system at high pressure and report on the surprising discovery of two stable compounds at pressures above 36 GPa, FeBi
2
and FeBi
3
. According to our predictions, FeBi
2
is a metal at the border of magnetism with a conventional electron-phonon mediated superconducting transition temperature of
T
c
= 1.3 K at 40 GPa.
We report the discovery of novel iron-bismuth compounds, FeBi
2
and FeBi
3
, at high-pressure.
Previous studies have shown that a large solid-state entropy of reduction increases the thermodynamic efficiency of metal oxides, such as ceria, for two-step thermochemical water splitting cycles. In ...this context, the configurational entropy arising from oxygen off-stoichiometry in the oxide, has been the focus of most previous work. Here we report a different source of entropy, the onsite electronic configurational entropy, arising from coupling between orbital and spin angular momenta in lanthanide f orbitals. We find that onsite electronic configurational entropy is sizable in all lanthanides, and reaches a maximum value of ≈4.7 k
per oxygen vacancy for Ce
/Ce
reduction. This unique and large positive entropy source in ceria explains its excellent performance for high-temperature catalytic redox reactions such as water splitting. Our calculations also show that terbium dioxide has a high electronic entropy and thus could also be a potential candidate for solar thermochemical reactions.Solid-state entropy of reduction increases the thermodynamic efficiency of ceria for two-step thermochemical water splitting. Here, the authors report a large and different source of entropy, the onsite electronic configurational entropy arising from coupling between orbital and spin angular momenta in f orbitals.
Intermetallic compounds with sizable band gaps are attractive for their unusual properties but rare. Here, we present a new family of stable semiconducting quaternary Heusler compounds, designed ...based on the 18-electron rule and discovered by means of high-throughput ab initio calculations based on the 18-electron rule. The 99 new semiconductors reported here adopt the ordered quaternary Heusler structure with the prototype of LiMgSnPd (F4̅3m, No. 216) and contain 18 valence electrons per formula unit. They are realized by filling the void in the half Heusler structure with a small and electropositive atom, i.e., lithium. These new stable quaternary Heusler semiconductors possess band gaps in the range of 0.3 to 2.5 eV, and exhibit some unusual properties different from conventional semiconductors, such as strong optical absorption, giant dielectric screening, and high Seebeck coefficient, which suggest these semiconductors have potential applications as photovoltaic and thermoelectric materials. While this study opens up avenues for further exploration of this novel class of semiconducting quaternary Heuslers, the design strategy used herein is broadly applicable across a potentially wide array of chemistries to discover new stable materials.
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