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The thermoelectric properties of polycrystalline binary narrow-bandgap intermetallic RuGa3 and RuIn3 compounds have been investigated in the temperature range from 373 K to 973 K. These compounds exhibit semiconductor-like transport properties with large Seebeck coefficients of -560 μV/K and 280 μV/K at 373 K for RuGa3 and RuIn3, respectively. The Seebeck coefficient of RuGa3 changed rapidly from large negative to large positive values around 500 K, which is consistent with our calculation based on the full-potential-linearized-augmented-plane-wave method. In contrast, RuIn3 is a p-type material at its operating temperature. The dimensionless figures of merit ZT of pure compounds reached maximum values of 0.13 and 0.17 at about 973 K and 773 K, respectively. The potential maximum ZT value was evaluated using the Boltzmann transport equation and can exceed unity by electron- or hole-doping for both compounds. By substituting Co for Ru in RuIn3, n-type thermoelectric materials (ZTmax = 0.10 at 473 K) were obtained. We suggest that ZT will be enhanced by further effective electron-doping. [ABSTRACT FROM AUTHOR]

The electrical and thermal transport properties of quaternary icosahedral Al71-xGaxPd20Mn9 (x=0,2,3,4) quasicrystals, obtained by replacing Al in icosahedral Al–Pd–Mn quasicrystal with Ga, have been measured in accordance with the guiding principle of “weakly bonded rigid heavy clusters” (WBRHCs). While the electrical conductivity and Seebeck coefficient were not dramatically changed, the thermal conductivity effectively decreased with increasing Ga concentration except for the sample with x=4. Although the thermoelectric properties do not obey the WBRHCs, the dimensionless figure of merit increased by a factor of 1.4 from 0.18 for Al71Pd20Mn9 to 0.26 for Al68Ga3Pd20Mn9 quasicrystal. [ABSTRACT FROM AUTHOR]

The electrical and thermal properties of quaternary icosahedral [Al.sub.71-x][Ga.sub.x][Pd.sub.20][Mn.sub.9] (x = 0, 2, 3, 4) quasicrystals are measured in accordance with the guiding principle of weakly bonded rigid heavy clusters (WBRHCs). The studies have shown that the control of the thermoelectric properties in these materials is the main obstacle for them from being a good thermoelectric material.

The size of structural vacancies and structural vacancy density of 1/1-Al–Re–Si approximant crystals with different Re compositions were evaluated by positron annihilation lifetime and Doppler broadening measurements. Incident positrons were found to be trapped at the monovacancy-size open space surrounded by Al atoms. From a previous analysis using the maximum entropy method and Rietveld method, such an open space is shown to correspond to the centre of Al icosahedral clusters, which locates at the vertex and body centre. The structural vacancy density of non-metallic Al73Re17Si10was larger than that of metallic Al73Re15Si12. The observed difference in the structural vacancy density reflects that in bonding nature and may explain that in the physical properties of the two samples. [ABSTRACT FROM PUBLISHER]

We investigated the electronic structure and thermoelectric properties of a ternary intermetallic compound AlFeSi composed only of abundant elements. First-principles band structure calculations implied that the target compound AlFeSi forms a narrow band gap of a few hundred meV near the Fermi level, indicating that both p- and n-type thermoelectric properties can be obtained by shifting the chemical potential. We present the thermoelectric properties of the narrow-band-gap intermetallic compound AlFeSi, which was synthesized by arc melting and spark plasma sintering. The conduction type could be controlled through changing the Al/Si ratio. The measured Seebeck coefficients were +55 and −90 μV K for p- and n-type materials, respectively. The obtained power factor was 370-400 μW m K in a mid-temperature region for both p- and n-type materials. Because of the low crystal symmetry of AlFeSi, the phonon thermal conductivity at 300 K exhibited a relatively low value of 4.5-5.5 W m K, despite being composed of relatively light elements. The estimated dimensionless figure of merit was found to be less than 0.04, which should be largely enhanced for practical applications. [ABSTRACT FROM AUTHOR]

The thermoelectric properties of MoSi2-type intermetallic compound Al6Re5Si4 (investigated compositions: Al6−xRe4.7Si4+x (x = 0–0.9)) related to TiSi2-type narrow band gap intermetallic compounds were systematically investigated. A first-principles band structure calculation implies that this compound forms a narrow band gap in the electronic density of states that will be suitable for obtaining a large power factor. Indeed, the maximum power factor is 1.65 mW m−1 K−2 for the sample with x = 0.8. The Al6−xRe4.7Si4+x (x = 0–0.8) samples show degenerate semiconductor behavior as p-type materials; the temperature coefficient of the electrical conductivity is negative and the positive Seebeck coefficient increases with increasing temperature. A negative Seebeck coefficient is observed in the Si-rich sample with x = 0.9, which is understood by shifting the Fermi level to the conduction band. The estimated band gap is 0.53 eV from the Arrhenius plot. Because of a simple crystal structure, a relatively high thermal conductivity ranging from 7.6 to 13.5 W m−1 K−1 is observed at 300 K. The maximum dimensionless figure-of-merit of 0.19 at 973 K is close to the optimal value predicted by a single parabolic band model. [ABSTRACT FROM AUTHOR]

The positron annihilation lifetime measurements for the Cd 17 Ca 3 quasicrystal and its 1/1 Cd 6 Ca approximant were carried out at 300?K. The observed lifetime of the Cd 17 Ca 3 quasicrystal is close to that of the 1/1 Cd 6 Ca approximant, implying the existence of the same type of structural vacancies. The temperature variations in the positron lifetime were investigated in the temperature region from 10 to 300?K for the Cd 17 Ca 3 quasicrystal annealed at 773?K and the Cd 17 Ca 3 quasicrystal cooled in the furnace. We found clear differences between both the absolute value and the temperature gradient of the positron lifetimes of the two quasicrystals. The results will be discussed in terms of the fluctuation in the four-Cd tetrahedron inside the 20-Cd dodecahedron between two quasicrystals. [ABSTRACT FROM AUTHOR]

Highlights: [•] The calculated structural parameters of hexagonal U3ZrSb5 are found in good agreement with the experimental data. [•] U3ZrSb5 is found to be ferromagnetic material. [•] Evident effects of the Hubbard U parameter in the uranium “5f” states are noted. [•] Our band structure calculation show the metallic behavior of this ferromagnetic compound. [•] The thermodynamic properties are predicted through the quasi-harmonic Debye model. [ABSTRACT FROM AUTHOR]

Highlights: [•] RuGa2 powder with the size ranged from 5 to 30 nm were obtained by ball-milling. [•] The bulk samples of RuGa2 were synthesized by spark plasma sintering. [•] The total thermal conductivity decreased by 31% using ball-milling at 300 K. [•] The maximum dimensionless figure of merit was 0.58 at 773 K for milled RuGa2. [Copyright &y& Elsevier]

Objective: This study aimed to reveal the effects of SET domain bifurcated 1 (SETDB1) on epithelial cells during tooth development., Design: We generated conditional knockout mice (Setdb1 fl/fl,Keratin14-Cre+ mice), in which Setdb1 was deleted only in epithelial cells. At embryonic day 14.5 (E14.5), immunofluorescence staining was performed to confirm the absence of SETDB1 within the epithelium of tooth embryos from Setdb1 fl/fl,Keratin14-Cre+ mice. Mouse embryos were harvested after reaching embryonic day 13.5 (E13.5), and sections were prepared for histological analysis. To observe tooth morphology in detail, electron microscopy and micro-CT analysis were performed at postnatal months 1 (P1M) and 6 (P6M). Tooth embryos were harvested from postnatal day 7 (P7) mice, and the epithelial components of the tooth embryos were isolated and examined using quantitative RT-PCR for the expression of genes involved in tooth development., Results: Setdb1 fl/fl,Keratin14-Cre+ mice exhibited enamel hypoplasia, brittle and fragile dentition, and significant abrasion. Coronal sections displayed abnormal ameloblast development, including immature polarization, and a thin enamel layer that detached from the dentinoenamel junction at P7. Electron microscopic analysis revealed characteristic findings such as an uneven surface and the absence of an enamel prism. The expression of Msx2, Amelogenin (Amelx), Ameloblastin (Ambn), and Enamelin (Enam) was significantly downregulated in the epithelial components of tooth germs in Setdb1 fl/fl,Keratin14-Cre+ mice., Conclusions: These results indicate that SETDB1 in epithelial cells is important for tooth development and clarify the relationship between the epigenetic regulation of SETDB1 and amelogenesis imperfecta for the first time., Competing Interests: Declaration of Competing Interest The authors declare no conflicts of interest., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

A quasicrystal is an ordered but nonperiodic structure understood as a projection from a higher-dimensional periodic structure. Some physical properties of quasicrystals are different from those of conventional solids. An anomalous increase in heat capacity at high temperatures has been discussed for over two decades as a manifestation of a hidden high dimensionality of quasicrystals. A plausible candidate for this origin has been the phason, which has excitation modes originating from the additional atomic rearrangements introduced by the quasiperiodic order, which can be understood in terms of shifting a higher-dimensional lattice. However, most theoretical studies of phasons have used toy models. A theoretical study of the heat capacity of realistic quasicrystals or their approximants has yet to be conducted because of the huge computational complexity. To bridge this gap between experiment and theory, we show experiments and molecular simulations on the same material, an Al-Pd-Ru quasicrystal, and its approximants. We show that at high temperatures, aluminum atoms diffuse with discontinuouslike jumps, and the diffusion paths of the aluminum can be understood in terms of jumps corresponding to hyperatomic-fluctuations-associated atomic rearrangements of the phason degrees of freedom. It is concluded that the anomaly in the heat capacity of quasicrystals arises from the hyperatomic fluctuations that play a role in diffusive Nambu-Goldstone modes.

The practical application of quasicrystals (QCs) as thermoelectric materials makes icosahedral ( i -) Al-Pd-Re QC attractive because of its moderate electrical conductivity (~280 Ω -1 cm -1 ), relatively high Seebeck coefficient (~100 μV K -1 ), and low thermal conductivity (~1.3 W m -1 K -1 ) at room temperature. To develop a thermoelectric Π-shaped power generation module, we need both p- and n-type thermoelectric materials. In this work, we aimed to develop an n-type i -Al-Pd-Re-based QC and investigated the effect of Co substitution for Re on the thermoelectric properties, i.e., the electron-doping effect. We synthesized dense bulk samples with nominal compositions of Al 71 Pd 20 (Re 1- x Co x ) 9 ( x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) via arc-melting, annealing, and sintering methods. We found that Co can produce n-type carriers in dilute substitution amounts of x = 0.1 and 0.2; however, the Seebeck coefficient at 300 K showed an n- to p-type transition with increasing x . This indicates that a simple rigid-band approximation is not applicable for i -Al-Pd-Re QC, which makes it difficult to synthesize an n-type i -Al-Pd-Re-based QC. Although the thermal conductivity was reduced from 1.28 ( x = 0) to 1.08 W m -1 K -1 ( x = 0.3) at 373 K by lowering of the electron thermal conductivity (electrical conductivity) and the alloying effect via Co substitution, the dimensionless figure of merit was not enhanced because of lowering of the power factor for all samples. The elastic moduli of i -Al-Pd-Re QC decreased by Co substitution, indicating that i -Al-Pd-Re-Co QC had a more ionic and brittle character.

To lower the introduction and maintenance costs of autonomous power supplies for driving Internet-of-things (IoT) devices, we have developed low-cost Fe-Al-Si-based thermoelectric (FAST) materials and power generation modules. Our development approach combines computational science, experiments, mapping measurements, and machine learning (ML). FAST materials have a good balance of mechanical properties and excellent chemical stability, superior to that of conventional Bi-Te-based materials. However, it remains challenging to enhance the power factor (PF) and lower the thermal conductivity of FAST materials to develop reliable power generation devices. This forum paper describes the current status of materials development based on experiments and ML with limited data, together with power generation module fabrication related to FAST materials with a view to commercialization. Combining bulk combinatorial methods with diffusion couple and mapping measurements could accelerate the search to enhance PF for FAST materials. We report that ML prediction is a powerful tool for finding unexpected off-stoichiometric compositions of the Fe-Al-Si system and dopant concentrations of a fourth element to enhance the PF, i.e., Co substitution for Fe atoms in FAST materials.

Icosahedral Al-Cu-Fe quasicrystal (QC) shows moderate electrical conductivity and low thermal conductivity, and both p- and n-type conduction can be controlled by tuning the sample composition, making it potentially suited for thermoelectric materials. In this work, we investigated the effect of introducing chemical disorder through heavy element substitution on the thermal conductivity of Al-Cu-Fe QC. We substituted Au and Pt elements for Cu up to 3 at% in a composition of Al 63 Cu 25 Fe 12 , i.e., Al 63 Cu 25- x (Au,Pt) x Fe 12 ( x = 0, 1, 2, 3). The substitutions of Au and Pt for Cu reduced the phonon thermal conductivity at 300 K ( κ ph,300K ) by up to 17%. The reduction of κ ph,300K is attributed to a decrease in the specific heat and phonon relaxation time through heavy element substitution. We found that increasing the Pt content reduced the specific heat at high temperatures, which may be caused by the locked state of phasons. The observed glass-like low values of κ ph,300K (0.9-1.1 W m -1 K - 1 at 300 K) for Al 63 Cu 25- x (Au,Pt) x Fe 12 are close to the lower limit calculated using the Cahill model.

Al 2 Fe 3 Si 3 intermetallic compound shows promising application in low-cost and non-toxic thermoelectric device because of its relatively high power factor of ∼700 μ W m -1  K -2 at 400 K. Herein we performed the first-principles calculations with the projector augmented-wave (PAW) method to study the formation energies, elastic constants, electronic structures, and electronic transport properties of Al 2 Fe 3 Si 3 . We discussed the thermodynamical stability of Al 2 Fe 3 Si 3 against other ternary crystalline compounds in Al-Fe-Si phase. The band gap of Al 2 Fe 3 Si 3 was particularly examined using the semilocal and hybrid functionals and the on-site Hubbard correction, which were also applied to β-FeSi 2 to calibrate the prediction reliability of our employed computational methods. Our calculations show that Al 2 Fe 3 Si 3 is a narrow-gap semiconductor. The semilocal functional within generalized gradient approximation (GGA) shows an exceptional agreement between the predicted band gap of Al 2 Fe 3 Si 3 and the available experiment data, which is in contrast to the typical trend and rationally understood through a comprehensive comparison. We found that both HSE06 and PBE0 hybrid functionals with a standard setup overestimated the band gaps of Al 2 Fe 3 Si 3 and β-FeSi 2 too much. The underlying reasons may be ascribed to a large electronic screening, which arises from the unique characteristics of Fe 3 d states appearing in both sides of band gaps of Al 2 Fe 3 Si 3 and β-FeSi 2 , and to a reduced delocalization error thanks to the covalent Fe-Si and Si-Si bonding nature. The chemical bonding and elasticity of Al 2 Fe 3 Si 3 were compared with those of β-FeSi 2 and FeAl 2 . In Al 2 Fe 3 Si 3 the Fe-Al bonding is more ionic and the Fe-Si bonding is more covalent. The elastic moduli of Al 2 Fe 3 Si 3 are comparable to those of β-FeSi 2 and larger than those of FeAl 2 . Our calculation results indicate that the mechanical strength of Al 2 Fe 3 Si 3 could be strong enough for the practical application in thermoelectric device., (© 2021 IOP Publishing Ltd.)

To develop an autonomous power generation technology to support an internet-of-things (IoT) society, we proposed low-cost and nontoxic Fe-Al-Si-based thermoelectric (FAST) materials consisting of an Fe 3 Al 2 Si 3 phase. Because of the cost-effectiveness and easy disposal of FAST materials, they are attractive for autonomous power supplies to drive IoT sensors and devices. While bismuth-tellurium-based thermoelectric power generation modules have been commercialized, the discovery of FAST materials opens an additional route to generate power from waste heat at room temperature under a small temperature difference, which will expand the diversity of applications of thermoelectric power generation modules. This paper reports the thermoelectric properties of FAST materials synthesized by conventional laboratory-scale synthesis and mass production processes, enhancement of power factor less than 600 K through homogenization and removal of metallic precipitations, development of thermoelectric power generation modules, and the results of power generation tests. The operation of temperature/humidity sensors and wireless transmission by Bluetooth low energy communication using FAST materials-based modules under a small temperature difference at room temperature was demonstrated.

Many monumental breakthroughs in p -type PbTe thermoelectrics are driven by optimizing a Pb 0.98 Na 0.02 Te matrix. However, recent works found that x > 0.02 in Pb 1- x Na x Te further improves the thermoelectric figure of merit, zT , despite being above the expected Na solubility limit. We explain the origins of improved performance from excess Na doping through computation and experiments on Pb 1- x Na x Te with 0.01 ≤ x ≤ 0.04. High temperature X-ray diffraction and Hall carrier concentration measurements show enhanced Na solubility at high temperatures when x > 0.02 but no improvement in carrier concentration, indicating that Na is entering the lattice but is electrically compensated by high intrinsic defect concentrations. The higher Na concentration leads to band convergence between the light L and heavy Σ valence bands in PbTe, suppressing bipolar conduction and increasing the Seebeck coefficient. This results in a high temperature zT nearing 2 for Pb 0.96 Na 0.04 Te, ∼25% higher than traditionally reported values for pristine PbTe-Na. Further, we apply a phase diagram approach to explain the origins of increased solubility from excess Na doping and offer strategies for repeatable synthesis of high zT Na-doped materials. A starting matrix of simple, high performing Pb 0.96 Na 0.04 Te synthesized following our guidelines may be superior to Pb 0.98 Na 0.02 Te for continued zT optimization in p -type PbTe materials.

Chemical composition alteration is a general strategy to optimize the thermoelectric properties of a thermoelectric material to achieve high-efficiency conversion of waste heat into electricity. Recent studies show that the Al 2 Fe 3 Si 3 intermetallic compound with a relatively high power factor of ∼700 μW m -1 K -2 at 400 K is promising for applications in low-cost and nontoxic thermoelectric devices. To accelerate the exploration of the thermoelectric properties of this material in a mid-temperature range and to enhance its power factor, a machine-learning method was employed herein to assist the synthesis of off-stoichiometric samples (namely, Al 23.5+ x Fe 36.5 Si 40- x ) of the Al 2 Fe 3 Si 3 compound by tuning the Al/Si ratio. The optimal Al/Si ratio for a high power factor in the mid-temperature range was found rapidly and efficiently, and the optimal ratio of the sample at x = 0.9 was found to increase the power factor at ∼510 K by about 40% with respect to that of the initial sample at x = 0.0. The possible mechanism for the enhanced power factor is discussed in terms of the precipitations of the metallic secondary phases in the Al 23.5+ x Fe 36.5 Si 40- x samples. Furthermore, the maximum achievable thermal conductivity of Al 2 Fe 3 Si 3 estimated by the Slack model is ∼10 W m -1 K -1 at the Debye temperature. An avoided-crossing behavior of the acoustic and the low-lying optical modes along several crystallographic directions is found in the phonon dispersion of Al 2 Fe 3 Si 3 calculated by ab initio density functional theory method. These preliminary results suggest that Al 2 Fe 3 Si 3 can have a low thermal conductivity. The calculated formation energies of point defects suggest that the antisite defects between Al and Si are likely to cause the Al and Si off-stoichiometries in Al 2 Fe 3 Si 3 . The theoretically obtained insight provides additional information for the further understanding of Al 2 Fe 3 Si 3 .