Abstract
Gravitational waves emitted from stellar binary black hole (sBBH) mergers can be gravitationally lensed by intervening galaxies and detected by future ground-based detectors. A great amount ...of effort has been put into the estimation of the detection rate of lensed sBBH originating from the evolution of massive binary stars (EMBS channel). However, sBBHs produced by the dynamical interaction in dense clusters (dynamical channel) may also be dominant in our universe and their intrinsic distribution of physical properties can be significantly different from those produced by massive stars, especially mass and redshift distribution. In this paper, we investigate the event rate of lensed sBBHs produced via the dynamical channel by Monte Carlo simulations and the number is
16
−
12
+
4.7
yr
−1
for the Einstein telescope and
24
−
17
+
6.8
yr
−1
for Cosmic Explorer, of which the median is about ∼2 times the rate of sBBHs originating from the EMBS channel (calibrated by the local merger rate density estimated for the dynamical and the EMBS channel, i.e.,
∼
14
−
10
+
4.0
and
19
−
3.0
+
42
Gpc
−
3
yr
−
1
, respectively). Therefore, one may constrain the fraction of both the EMBS and dynamical channels through the comparison of the predicted and observed number of lensed sBBH events statistically.
For several decades, thermoelectric advancements have largely relied on the reduction of lattice thermal conductivity (κL). According to the Boltzmann transport theory of phonons, κL mainly depends ...on the specific heat, the velocity, and the scattering of phonons. Intensifying the scattering rate of phonons is the focus for reducing the lattice thermal conductivity. Effective scattering sources include 0D point defects, 1D dislocations, and 2D interfaces, each of which has a particular range of frequencies where phonon scattering is most effective. Because acoustic phonons are generally the main contributors to κL due to their much higher velocities compared to optical phonons, many low‐κL thermoelectrics rely on crystal structure complexity leading to a small fraction of acoustic phonons and/or weak chemical bonds enabling an overall low phonon propagation velocity. While these thermal strategies are successful for advancing thermoelectrics, the principles used can be integrated with approaches such as band engineering to improve the electronic properties, which can promote this energy technology from niche applications into the mainstream.
Phonon transport is reviewed, considering its guiding principles, and including a summary of newly proven strategies and further considerations for κL‐minimization. Most of the strategies presented can effectively reduce the lattice thermal conductivity, which leads to a great increase in thermoelectric performance in many materials.
The autoimmune disease amyopathic dermatomyositis–associated interstitial lung disease, which is related to anti–melanoma differentiation–associated protein 5 antibodies, is often rapidly ...progressive. Patients who received glucocorticoids and tofacitinib had improved survival.
GeTe-based alloys have been intensively considered as p-type thermoelectrics for about 50 years, yet existing literature barely discussed the thermoelectric properties of pristine GeTe at high ...temperatures (300–800 K). This work first backs to a fundamental understanding on the thermoelectric transport properties inherent to p-type GeTe, based on more than 50 samples synthesized with expected carrier concentrations ranging from 1 × 1020 to 3 × 1021 cm–3. A thermoelectric figure of merit zT as high as ∼1.7 is found inherent to this compound when it is optimally doped with a Hall carrier concentration of 2.2 ± 10% × 1020 cm–3, offering a reference substance to expose the origins for the high zT in historical GeTe-based alloys. Guided by the above knowledge, further alloying Te with Se in samples with an optimal carrier concentration enables a reduction on the lattice thermal conductivity by ∼40% and eventually leads to a further enhancement on zT (up to 2.0) by ∼20%. This work demonstrates not only GeTe as an inherently high performance thermoelectric matrix compound but also its availability for further improvements by additional strategies.
Optimization of carrier concentration plays an important role on maximizing thermoelectric performance. Existing efforts mainly focus on aliovalent doping, while intrinsic defects (e.g., vacancies) ...provide extra possibilities. Thermoelectric GeTe intrinsically forms in off-stoichiometric with Ge-vacancies and Ge-precipitates, leading to a hole concentration significantly higher than required. In this work, Sb2Te3 having a smaller cation-to-anion ratio, is used as a solvend to form solid solutions with GeTe for manipulating the vacancies. This is enabled by the fact that each substitution of 3 Ge2+ by only 2 Sb3+ creates 1 Ge vacancy, because of the overall 1:1 cation-to-anion ratio of crystallographic sites in the structure and by the charge neutrality. The increase in the overall Ge-vacancy concentration facilitates Ge-precipitates to be dissolved into the matrix for reducing the hole concentration. In a combination with known reduction in hole concentration by Pb/Ge-substitution, a full optimization on hole concentration is realized. In addition, the resultant high-concentration point defects including both vacancies and substitutions strongly scatter phonons and reduce the lattice thermal conductivity to the amorphous limit. These enable a significantly improved thermoelectric figure of merit at working temperatures of thermoelectric GeTe.
High-efficiency thermoelectric materials require a high conductivity. It is known that a large number of degenerate band valleys offers many conducting channels for improving the conductivity without ...detrimental effects on the other properties explicitly, and therefore, increases thermoelectric performance. In addition to the strategy of converging different bands, many semiconductors provide an inherent band nestification, equally enabling a large number of effective band valley degeneracy. Here we show as an example that a simple elemental semiconductor, tellurium, exhibits a high thermoelectric figure of merit of unity, not only demonstrating the concept but also filling up the high performance gap from 300 to 700 K for elemental thermoelectrics. The concept used here should be applicable in general for thermoelectrics with similar band features.
Compared to commercially available p‐type PbTe thermoelectrics, SnTe has a much bigger band offset between its two valence bands and a much higher lattice thermal conductivity, both of which limit ...its peak thermoelectric figure of merit, zT of only 0.4. Converging its valence bands or introducing resonant states is found to enhance the electronic properties, while nanostructuring or more recently introducing interstitial defects is found to reduce the lattice thermal conductivity. Even with an integration of some of the strategies above, existing efforts do not enable a peak zT exceeding 1.4 and usually involve Cd or Hg. In this work, a combination of band convergence and interstitial defects, each of which enables a ≈150% increase in the peak zT, successfully accumulates the zT enhancements to be ≈300% (zT up to 1.6) without involving any toxic elements. This opens new possibilities for further improvements and promotes SnTe as an environment‐friendly solution for conventional p‐PbTe thermoelectrics.
A combination of band convergence by alloying with MnTe and interstitial defect scattering by alloying with Cu2Te, each of which enables an ≈150% increase in the peak thermoelectric figure of merit, zT of SnTe, successfully accumulates the zT enhancements to be ≈300% without involving any toxic elements. This promotes SnTe as an eco‐friendly solution for p‐PbTe thermoelectrics.
To minimize the lattice thermal conductivity in thermoelectrics, strategies typically focus on the scattering of low-frequency phonons by interfaces and high-frequency phonons by point defects. In ...addition, scattering of mid-frequency phonons by dense dislocations, localized at the grain boundaries, has been shown to reduce the lattice thermal conductivity and improve the thermoelectric performance. Here we propose a vacancy engineering strategy to create dense dislocations in the grains. In Pb
Sb
Se solid solutions, cation vacancies are intentionally introduced, where after thermal annealing the vacancies can annihilate through a number of mechanisms creating the desired dislocations homogeneously distributed within the grains. This leads to a lattice thermal conductivity as low as 0.4 Wm
K
and a high thermoelectric figure of merit, which can be explained by a dislocation scattering model. The vacancy engineering strategy used here should be equally applicable for solid solution thermoelectrics and provides a strategy for improving zT.
Phonon scattering by nanostructures and point defects has become the primary strategy for minimizing the lattice thermal conductivity (κL) in thermoelectric materials. However, these scatterers are ...only effective at the extremes of the phonon spectrum. Recently, it has been demonstrated that dislocations are effective at scattering the remaining mid‐frequency phonons as well. In this work, by varying the concentration of Na in Pb0.97Eu0.03Te, it has been determined that the dominant microstructural features are point defects, lattice dislocations, and nanostructure interfaces. This study reveals that dense lattice dislocations (≈4 × 1012 cm−2) are particularly effective at reducing κL. When the dislocation concentration is maximized, one of the lowest κL values reported for PbTe is achieved. Furthermore, due to the band convergence of the alloyed 3% mol. EuTe the electronic performance is enhanced, and a high thermoelectric figure of merit, zT, of ≈2.2 is achieved. This work not only demonstrates the effectiveness of dense lattice dislocations as a means of lowering κL, but also the importance of engineering both thermal and electronic transport simultaneously when designing high‐performance thermoelectrics.
Eu‐doping effectively converges the valence bands of PbTe, while Na‐doping enables dense lattice dislocations, leading to an extremely low lattice thermal conductivity (κL) of <0.4 W m−1 K−1. This contributes to a high zT of ≈2.2, opening new possibilities for advancing thermoelectrics through dislocation and band‐engineering approaches.
Advancing thermoelectric n‐type Mg3Sb2 alloys requires both high carrier concentration offered by effective doping and high carrier mobility enabled by large grains. Existing research usually ...involves chalcogen doping on the anion sites, and the resultant carrier concentration reaches ≈3 × 1019 cm−3 or below. This is much lower than the optimum theoretically predicted, which suggets that further improvements will be possible once a highly efficient dopant is found. Yttrium, a trivalent dopant, is shown to enable carrier concentrations up to and above ≈1 × 1020 cm−3 when it is doped on the cation site. Such carrier concentration allows for in‐depth understand of the electronic transport properties over a broad range of carrier concentrations, based on a single parabolic band approximation. As well as reasonably high carrier mobility in coarse‐grain materials sintered by hot deforming and fusing of large pieces of ingots synthesized by melting, higher thermoelectric performance than earlier experimentally reported for n‐type Mg3Sb2 is found. In particular, the thermoelectric figure of merit, zT, is even higher than that of any known n‐type thermoelectric, including Bi2Te3 alloys, within 300–500 K. This might pave the way for Mg3Sb2 alloys to become a realistic material for n‐type thermoelectrics for sustainable applications.
Yttrium is found to be an effective dopant for obtaining electron concentrations as high as ≈1020 cm−3 in Mg3SbBi. This leads to extraordinary thermoelectric performance and high thermal stability.
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