Sb Sites Research Articles

Enhanced thermoelectric performance of Bi0.5Sb1.5Te3 via Ni-doping: A Shift of peak ZT at elevated temperature via suppressing intrinsic excitation

Bi2Te3-based thermoelectric (TE) materials have been demonstrated to be a potential candidate for mainly thermoelectric cooling/refrigeration applications. However, minority charge carriers excitation at high temperature reduces thermopower which restricts these materials for the use in power generation. In present work, substitution of Ni on Sb site in Bi0.5Sb1.5-xNixTe3 (x = 0, 0.01, 0.04 and 0.08) actuates the system to supress the intrinsic excitation leading to shift in highest ZT to higher temperature regime. The Density functional theory (DFT) calculations and experimental results reveal that Ni in Bi0.5Sb1.5Te3 provides the extra holes and slightly reduces the band gap Eg which enhances the σ of Ni-doped Bi0.5Sb1.5-xNixTe3 samples and α at elevated temperature. Moreover, Ni-doping in Bi0.5Sb1.5Te3 also reduces κL which is attributed to the phonon scattering due to mass fluctuations and microstructural features such as grain boundary and strain field domain observed from HRTEM investigation. These favourable condition leads to maximum ZT∼1.38 at 433K for Bi0.5Sb1.46Ni0.04Te3 and ZTavg ∼1.1 between 300K and 503K. Interestingly the calculated theoretical TE conversion device efficiency η of Bi0.5Sb1.46Ni0.04Te3 (η∼5.5%) was achieved to be nearly twice than the efficiency of matrix Bi0.5Sb1.5Te3 (η∼3%). Experimental electronic transport is well corroborated with theoretically estimated DFT results.

The antiferromagnetic to ferrimagnetic phase transition in Mn2Sb1-xBix compounds

The influence of partial substitution of Bi for Sb on the structure, magnetic properties and magnetocaloric effect of Mn2Sb1-xBix (x = 0, 0.02, 0.04, 0.05, 0.07, 0.09, 0.15, 0.20) compounds has been investigated. The transition temperature of the antiferro-to-ferrimagnetic (AFM-FIM) transition initially increases with increasing Bi and decreases above 9%. Density functional theory calculations indicate that the Bi atoms prefer to occupy only the Sb site, which accounts for the large magnetization jump in Mn2Sb0.93Bi0.07. As large lattice parameters are found for Bi substituted Mn2Sb, the origin of the AFM-FIM transition in Mn2Sb(1-x)Bix compounds is ascribed to an enhanced coefficient of thermal expansion along the c axis, resulting from the Bi substitution. The moderate entropy change of 1.17 J/kg K under 2 T originating from the inverse magnetocaloric effect and the strong magnetic field dependence of the transition temperature of dTt/dµ0H = −5.4 K/T in Mn2Sb0.95Bi0.05 indicate that this alloy is a promising candidate material for magnetocaloric applications.

Effect of Bi-substitution on structural stability and improved thermoelectric performance of p-type half-Heusler TaSbRu: A first-principles study

Recently, Fang et al. have predicted a high thermoelectric (TE) figure of merit (ZT) of 1.54 in TaSbRu alloys at 1200 K from first-principles calculations without considering spin-orbit interaction, accurate electronic structure, details of phonon scattering, and energy-dependent holes relaxation time. Here, we report the details of structural stability and thermoelectric performance of Bi-substituted p-type TaSbRu from first-principles calculations considering these important parameters. This indirect bandgap semiconductor (Eg = 0.8 eV by Tran-Blaha modified Becke Jonshon potential (TB-mBJ) including spin-orbit coupling (SOC) effect) has highly dispersive and degenerate valence bands, which lead to a maximum power factor, 3.8 mW m−1 K−2 at 300 K. As Sb-5p has a small contribution to the bandgap formation, the substitution of Bi on the Sb site does not cause significant change to the electronic structure. Although the Seebeck coefficient increases by Bi due to slight changes in the bandgap, electrical conductivity decreases, and hence, the power factor reduces to ~3 mW m−1 K−2 at 300 K (50% Bi). On the other side, lattice thermal conductivity drops effectively to 5 from 20 W m−1 K−1 as Bi introduces a significant contribution to the acoustic phonons and intensifies phonon scattering. Thus, ZT value is improved through Bi-substitution, reaching 1.1 (50% Bi) at 1200 K from 0.45 (pure TaSbRu) only. Therefore, the present study suggests how to improve the TE performance of Sb-based half-Heusler compounds and TaSbRu (with 50% Bi) is a promising material for high-temperature TE applications.

Polycomponent doping improved thermoelectric performance of Cu<sub>3</sub>SbSe<sub>4</sub>-based solid solutions

<sec> Cu<sub>3</sub>SbSe<sub>4</sub>, one of the ternary p-type semiconductor materials with chalcopyrite structure, has aroused much interest in thermoelectrics due to its inherent large effective mass and narrow bandgap. Therefore, many researches have been done, which cover the single and/or multi-element doping to manipulate its band structure and introduce the point defects. Although great achievements have been made in recent years, the mechanism in Cu<sub>3</sub>SbSe<sub>4</sub> with respect to the phonon and electronic transport properties needs further investigating. </sec><sec> In this work, first, Sn and S are co-doped into Cu<sub>3</sub>SbSe<sub>4</sub> and then the resulting compound is alloyed with Ga<sub>2</sub>Te<sub>3</sub>, to improve its TE performance and understand the mechanism by calculating the band structure and crystal structure. The calculation of band structure reveals that an impurity band is created within the bandgap after co-doping Sn and S due to their contributions to the density of the states (DOS), which is directly responsible for the significant improvement in carrier concentration (<i>n</i><sub>H</sub>) and electrical property. Therefore, the power factor (PF) is enhanced from 0.52 × 10<sup>–3</sup> to 1.3 × 10<sup>–3</sup> W·m<sup>–1</sup>·K<sup>–2</sup>. </sec><sec> Although the effect associated with the Ga (Te) residing at Sb (Se) sites on the band structure is limited due to the fact that both the single Ga- and single Te-doped band structure remain almost unchanged, the structural parameters (bond lengths and angles) of the polyhedrons [SeCu<sub>3</sub>Sb] and [SbSe<sub>4</sub>] before and after Te and Ga residing at Se and Sb sites respectively change remarkably. This yields the significant distortion of local lattice structure on an atomic scale. Therefore, the phonon scattering is enhanced and the lattice thermal conductivity (<i>κ</i><sub>L</sub>) decreases from 1.23 to 0.81 W·K<sup>–1</sup>·m<sup>–1</sup> at 691 K. The reduction in <i>κ</i><sub>L</sub> prevents the total thermal conductivity (<i>κ</i>) from being enhanced rapidly. As a consequence, the highest ZT value of 0.64 is attained, which is much higher than that of the pristine Cu<sub>3</sub>SbSe<sub>4</sub> (ZT = 0.26). In addition, we not only present a synergistic strategy to separately optimize the phonon and electronic properties, but also fully elaborate its mechanism and better understand that this strategy is an effective way to improve the TE performance of the Cu<sub>3</sub>SbSe<sub>4</sub>-based solid solutions.</sec>

Realizing ultralow thermal conductivity in Cu3SbSe4 via all-scale phonon scattering by co-constructing multiscale heterostructure and IIIB element doping

This article attempts to realize ultralow lattice thermal conductivity in Cu3SbSe4 by substitution Sb site by IIIB elements (Sc/Y), the facial microwave reaction were chosen to fabricate the above samples. The results show that group IIIB elements combined with multiscale heterostructure can effectively suppress the lattice thermal conductivity in Cu3SbSe4 system, resulting in a typical low value of 0.491 W/m/K and 0.481 W/m/K in Cu3Sb0.92Sc0.08Se4 and Cu3Sb0.92Y0.08Se4 at 623 K, respectively. Eventually, a peaking zT value of 0.47 and 0.46 can be obtained for each doping sample. This research highlights a novel strategy by co-constructing multiscale heterostructure and IIIB elements doping for realizing multiscale phonon scattering in Cu3SbSe4 materials.

G0W0 plus BSE calculations of quasiparticle band structure and optical properties of nitrogen-doped antimony trisulfide for near infrared optoelectronic and solar cells application

Theoretical calculations of structural, electronic, excitonic and optical properties of N-doped Sb2S3 are studied using highly accurate first-principles approach within many-body perturbation theory (MBPT) formalism. The calculated structural parameters of undoped Sb2S3 within Wu-Cohen’s generalized gradient approximation (WC-GGA) are reasonably close to those obtained in experimental measurement. Many-body perturbation theory (MBPT) based on the G0W0 approximation is used for the quasiparticle (QP) band structure. The bandgap value of 1.70 eV for the undoped Sb2S3 crystal within G0W0 approximation is consistent with the experimental value of 1.70–1.80 eV. When one atom of N is introduced into Sb2S3 at Sb site, the doping effects modified the band gap from 1.70 to 1.17 eV. Also, by introducing one atom of N to S site, the band gap value reduced to 0.96 eV. Our findings confirmed that non-metal doping narrow the energy gap of semiconductor materials. The optical properties of pure and N-doped Sb2S3 are computed using G0W0 plus Bethe-Salpeter Equation (BSE) which include both electron-electron (e-e) and electron-hole (e-h) interactions. The optical gap for Sb16S24, Sb15N1S24 and Sb16S23N1 were found to be 1.54, 0.97 and 0.82 eV, respectively. The narrowing effects and strong optical absorption of N-doped Sb2S3 suggest that the investigated material is suitable for solar cells and near infrared optoelectronic applications.

The reduction of thermal conductivity in Cd and Sn co-doped Cu3SbSe4-based composites with a secondary-phase CdSe

In this paper, we reported the enhanced thermoelectric properties of Cd and Sn dual-doped Cu3SbSe4-based material prepared by the vacuum melting combined with spark plasma sintering process. X-ray photoelectron spectroscopy studies revealed the presence of Cu+, Cd2+, Sb5+, Sn4+ and Se2− states of Cu, Cd, Sb, Sn and Se, respectively. All samples exhibited p-type conduction with carrier concentrations varying from 0.54 × 1018 to 46.42 × 1018 cm−3, while carrier mobility changes from 18.2 to 46.6 cm2 V−1 s−1 at room temperature. Cd doping at Cu sites in the Cu3SbSe4 can reduce the lattice thermal conductivity, while Sn doping at Sb sites is effective to adjust the carrier concentration. The further reduction in thermal conductivity is observed in Cd-Sn co-doped samples resulting from an accumulated effect combining point defects and the secondary-phase CdSe. Consequently, the maximum dimensionless figure of merit (ZT) value reaches 0.66 at 623 K for the Cu2.75Cd0.25Sb0.94Sn0.06Se4 sample, which is 190% larger than that of the intrinsic sample (ZT of 0.35). The findings provide an alternative strategy of boosting the carrier and phonon transports of the Cu3SbSe4, which is also a meaningful guidance to achieve high performance in other copper-based chalcogenides.

Absence of Magnetic Proximity Effect at the Interface of Bi_{2}Se_{3} and (Bi,Sb)_{2}Te_{3} with EuS.

We performed x-ray magnetic circular dichroism (XMCD) measurements on heterostructures comprising topological insulators (TIs) of the (Bi,Sb)_{2}(Se,Te)_{3} family and the magnetic insulator EuS. XMCD measurements allow us to investigate element-selective magnetic proximity effects at the very TI/EuS interface. A systematic analysis reveals that there is neither significant induced magnetism within the TI nor an enhancement of the Eu magnetic moment at such interface. The induced magnetic moments in Bi, Sb, Te, and Se sites are lower than the estimated detection limit of the XMCD measurements of ∼10^{-3} μ_{B}/at.

Enhanced thermoelectric performance of p-type ZrCoSb0.9Sn0.1 via Tellurium doping

Doping strategy has been shown as an effective paradigm in most of the thermoelectric materials for optimization of high ZT. Herein, we have synthesized several compositions of Te doped p-type ZrCoSb0.9-xSn0.1Tex (0≤ × ≤0.08) Half-Heusler (HH) alloys employing arc melting followed by spark plasma sintering (SPS). X-ray Diffraction (XRD) analysis reveals the formation of single phase of MgAgAs type HH phase. Thermoelectric properties were measured from room temperature to 773 K. Interestingly, Te doping on Sb site in ZrCoSb0.9-xSn0.1Tex leads to decrease of lattice thermal conductivity and a minimum lattice thermal conductivity~ 1.98 WK−1m−1 at 773 K for composition ZrCoSb0.9-xSn0.1Tex (x = 0.08) was optimized. The reduction in thermal conductivity is attributed to scattering of phonons by mass fluctuation and grain boundaries. In addition to this, significant improvement in power factor (~16.89 μWK−2cm−1at 773K) for ZrCoSb0.9-xSn0.1Tex (x = 0.06) was observed to be optimized. The enhancement in power factor is mainly attributed due to increased Seebeck coefficient manifested by reduction in effective hole carrier density occurred by Te substitution on Sb site. Thus, combination of reduced thermal conductivity and enhanced power factor obtained via Te substitution at Sb site leads to a high ZT~ 0.53 for ZrCoSb0.9-xSn0.1Tex (x = 0.06). The present ZT~ 0.53 optimized for ZrCoSb0.9-xSn0.1Tex (x = 0.06) is 150% larger than that of un-doped ZrCoSb0.9Sn0.1 compound.

Instant Postsynthesis Aqueous Dispersion of Sb-Doped SnO2 Nanocrystals: The Synergy between Small-Molecule Amine and Sb Dopant Ratio.

Direct printing of transparent conducting oxide (TCO) nanocrystal dispersions holds great promise in solution-processed optoelectronics due to its advantages of low material waste and direct patterning on substrates. An essential prerequisite for printable TCO colloidal solutions is the effective stabilization of TCO nanocrystals to prevent their strong aggregation. In situ stabilization uses long-chain ligands to provide interparticle steric repulsion between TCO nanocrystals during the growth of TCO nanocrystals. In sharp contrast, the postsynthesis dispersion of TCO nanocrystals is particularly challenging since the agglomeration already occurs, especially for TCO nanocrystals synthesized without protection by any organic species. Herein, we propose an instant postsynthesis strategy for aqueous colloidal dispersions of Sb-doped SnO2 (ATO) nanocrystals using small-molecule amines of propylamine, ethylenediamine, monoethanolamine, and triethylamine. The average size of ATO secondary particles in aqueous dispersions can be instantly reduced from around 400 to about 25 nm using these amines. The increased Sb dopant ratio also plays a synergistic role in the dispersion effect. The small-molecule amines are found to be preferably adsorbed onto the Sb sites exposed on ATO nanocrystal surface. A higher Sb dopant ratio would facilitate the adsorption of more amines and induce stronger surface charge repulsion that benefits the stable dispersion of ATO nanocrystals. TCO films fabricated with the ATO nanocrystal dispersions have a high transparency of 80.6% and low sheet resistance of 492 Ω/sq, showing promising application in electrochromic devices.

Hybrid structure responsible for improved thermoelectric performance of Sn-incorporated Cu3SbSe4 with a second phase CuSe

In this work, we design and synthesize a hybrid structure consisting of Sn-incorporated Cu3SbSe4 and a second phase CuSe, that is, (Cu3Sb1 − xSnxSe4)(CuSe)y (x = 0–0.04, y = 0.3–0.08), and explore the role of each phase on the improvement of the thermoelectric (TE) performance. In the Cu3Sb1 − xSnxSe4 phase, the element Sn residing at the Sb site provides p-type holes while at the same time increasing the point defects and crystal structure distortion. The presence of the second phase CuSe, which is in situ formed within the Cu3Sb1 − xSnxSe4 matrix, not only improves the electrical conductivity but also increases the phonon scattering on the phase boundaries. As a result, the hybrid structure allows the improvement in TE performance with the highest ZT value of 0.37 at ∼600 K for the samples at x = 0.02–0.03 and y = 0.11–0.09, which is about 42% higher than that of pristine Cu3SbSe4. This work reveals us a new method of improving TE performance, that is, through organizing a hybrid structure in Cu3SbSe4-based composites.

Enhanced Thermoelectric Properties in p‐Type Double Half‐Heusler Ti2−yHfyFeNiSb2−xSnx Compounds

Double half‐Heusler Ti2FeNiSb2‐based compounds, which can be regarded as a combination of 17‐electron TiFeSb and 19‐electron TiNiSb, have a lower intrinsic thermal conductivity due to the smaller group velocity phonons and the disordered scattering by Fe/Ni. An enhanced room‐temperature Hall carrier concentration of ≈4.8 × 1021 cm−3 is achieved by doping Sn on the Sb site in a series of Ti2FeNiSb2−xSnx (x = 0.2, 0.3, 0.4, and 0.5) samples. Combined with the further decreased lattice thermal conductivity by alloying with Hf2FeNiSb2, a low lattice thermal conductivity of ≈1.95 W m−1 K−1 and a peak thermoelectric figure of merit (ZT) of ≈0.52 at 923 K are obtained in Ti1.6Hf0.4FeNiSb1.7Sn0.3, indicating the promising applications of double half‐Heusler compounds.

Optimization of electrical and thermal transport properties of Fe0.25Co0.75Sb3 Skutterudite employing the isoelectronic Bi-doping

The practical applications of unfilled CoSb3-based Skutterudites for thermoelectric (TE) devices have been limited primarily owing to their bipolar conduction behaviour, which is detrimental for the TE performance. In the present studies, a peak TE figure-of-merit (ZT)max ~ 0.7 at 860 K has been realized with a pioneering (ZT)average ~ 0.34 in p-type CoSb3 co-doped by Fe and Bi at an optimal composition of Fe0.25Co0.75Sb2.995Bi0.005. The synthesis route for the alloy was the combination of arc melting and the spark plasma sintering. The TE properties measurement results suggest that the Fe doping at the Co site in CoSb3 lead to the unipolar p-type conduction while Bi substitution at Sb site helps in reducing the thermal conductivity via enhanced point defect induced phonon scattering. The synthesized samples were characterised for phase, morphology and structure using X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy, based on which some TE properties of the synthesized samples have also been discussed. In addition, the effect of magnetic entropy on the TE performance has also been studied experimentally as well as theoretically. The first-principles based density functional theory has been employed for the theoretical calculation of the electronic band-structure, electrical transport properties and the magnetic moment, which are found to be in fair agreement with the experimental observations.

Chemical and Biological Characterization of Particulate Matter (PM 2.5) and Volatile Organic Compounds Collected at Different Sites in the Los Angeles Basin

Background: Most studies on air pollution (AP) exposure have focused on adverse health effects of particulate matter (PM). Less well-studied are the actions of volatile organic compounds (VOCs) not retained in PM collections. These studies quantified chemical and biological properties of both PM2.5 and VOCs. Methods: Samples were collected near the Port of Los Angeles (Long Beach, LB), railroads (Commerce, CM), and a pollution-trapping topography-site (San Bernardino, SB). Quantitative assays were conducted: (1) chemical—prooxidant and electrophile content, (2) biological—tumor necrosis factor-α (TNF-α) and heme oxygenase-1 (HO-1) expression (3), VOC modulation of PM effects and (4), activation of the antioxidant response element (ARE) using murine RAW 264.7 macrophages. Results: SB site samples were the most potent in the chemical and biological assays, followed by a CM railroad site. Only PM2.5 exhibited significant proinflammatory responses. VOCs were more potent than PM2.5 in generating anti-inflammatory responses; further, VOC pretreatment reduced PM-associated TNF-α expression. VOCs significantly increased ARE activation compared to their corresponding PM2.5 which remained at background levels. Conclusion: Ambient VOCs are major contributors to adaptive responses that can modulate PM effects, in vitro, and, as such, need to be included in comprehensive assessments of AP.

Solid-State Synthesis and Thermoelectric Properties of Tetrahedrites Cu12Sb4-yBiyS13

Tetrahedrite has low lattice thermal conductivity because of the lone-pair electrons of Sb, which cause the Cu atoms to vibrate at a low frequency and high amplitude. The synthesis of tetrahedrite compounds by conventional melting methods requires a long-time reaction and annealing. However, a homogeneous and solid-state synthesis can be conducted in a short time using mechanical alloying (MA) because the volatilization of the constituent elements is inhibited and a subsequent heat treatment is not necessary. In this study, Bi-doped tetrahedrites Cu12Sb4-yBiyS13 (y = 0-0.4) were prepared by MA and hot pressing. X-ray diffraction analyses revealed that all specimens consisted of single-phase tetrahedrite. However, with increasing Bi content, skinnerite Cu3SbS3 was detected. The electrical conductivity increased and the Seebeck coefficient deceased with increasing Bi content as result of the substitution of Bi at Sb sites. In addition, the thermal conductivity increased as the Bi content increased because of the increase in electronic thermal conductivity. A high dimensionless figure of merit of 0.88 was obtained at 723 K for Cu12Sb3.9Bi0.1S13.

Significant role of nanoscale Bi-rich phase in optimizing thermoelectric performance of Mg3Sb2**Project supported by the National Natural Science Foundation of China (Grant Nos. 51371010, 51572066, and 50801002), the Beijing Municipal Natural Science Foundation, China (Grant No. 2112007), the Fundamental Research Funds for the Central Universities (Grant No. PXM2019-014204-500032), and the Science Fund from the Advanced Space Propulsion Laboratory of BICE

Mg3Sb1.5Bi0.5-based alloys have received much attention, and current reports on this system mainly focus on the modulation of doping. However, there lacks the explanation for the choice of Mg3Sb1.5Bi0.5 as matrix. Here in this work, the thermoelectric properties of Mg3Sb2−xBix (0.4 ≤ x ≤ 0.55) compounds are systematically investigated by using the first principles calculation combined with experiment. The calculated results show that the band gap decreases after Bi has been substituted for Sb site, which makes the thermal activation easier. The maximum figure of merit (ZT) is 0.27 at 773 K, which is attributed to the ultra-low thermal conductivity 0.53 W·m−1·K−1 for x = 0.5. The large mass difference between Bi and Sb atoms, the lattice distortion induced by substituting Bi for Sb, and the nanoscale Bi-rich particles distributed on the matrix are responsible for the reduction of thermal conductivity. The introduction of Bi into Mg3Sb2-based materials plays a vital role in regulating the transport performance of thermoelectric materials.

Improvement of thermoelectric property in Ce filled Fe3Co1Sb12 by Sn addition

Co and Sn-doped/added p-type skutterudite was prepared to examine the reduction of the electronic thermal conductivity. Samples with the nominal compositions of Ce0.95Fe4Sb12.2, Ce0.95Fe3Co1Sb12.2, Ce0.95-xSnxFe3Co1Sb12.2 (x = 0.1, 0.2, 0.3), ySn-Ce0.95Fe3Co1Sb12.2 (y = 0.1, 0.2, 0.3) were synthesized by heat treatment, melt-spinning followed by spark plasma sintering. In Ce0.95Fe3Co1Sb12.2 and ySn-Ce0.95Fe3Co1Sb12.2 single skutterudite phase was detected by XRD. ySn-Ce0.95Fe3Co1Sb12.2 has lower electrical conductivity and higher Seebeck coefficient than Ce0.95Fe3Co1Sb12.2, which result in higher power factor and lower electronic thermal conductivity of ySn-Ce0.95Fe3Co1Sb12.2. EXAFS spectra confirmed that Sn occupies the Sb site. Sn seems to compensate the defect of Sb in Ce0.95Fe3Co1Sb12.2 and supplied electron carriers. The ZT value of 0.2Sn–Ce0.95Fe3Co1Sb12.2 reached 0.9 at 673 K, which is 30% higher than that of Ce0.95Fe3Co1Sb12.2 prepared in this study.

Chemically driven superstructural ordering leading to giant unit cells in unconventional clathrates Cs8Zn18Sb28 and Cs8Cd18Sb28.

The unconventional clathrates, Cs8Zn18Sb28 and Cs8Cd18Sb28, were synthesized and reinvestigated. These clathrates exhibit unique and extensive superstructural ordering of the clathrate-I structure that was not initially reported. Cs8Cd18Sb28 orders in the Ia3̄d space group (no. 230) with 8 times larger volume of the unit cell in which most framework atoms segregate into distinct Cd and Sb sites. The structure of Cs8Zn18Sb28 is much more complicated, with an 18-fold increase of unit cell volume accompanied by significant reduction of symmetry down to P2 (no. 3) monoclinic space group. This structure was revealed by a combination of synchrotron X-ray diffraction and electron microscopy techniques. A full solid solution, Cs8Zn18−xCdxSb28, was also synthesized and characterized. These compounds follow Vegard's law in regard to their primitive unit cell sizes and melting points. Variable temperature in situ synchrotron powder X-ray diffraction was used to study the formation and melting of Cs8Zn18Sb28. Due to the heavy elements comprising clathrate framework and the complex structural ordering, the synthesized clathrates exhibit ultralow thermal conductivities, all under 0.8 W m−1 K−1 at room temperature. Cs8Zn9Cd9Sb28 and Cs8Zn4.5Cd13.5Sb28 both have total thermal conductivities of 0.49 W m−1 K−1 at room temperature, among the lowest reported for any clathrate. Cs8Zn18Sb28 has typical p-type semiconducting charge transport properties, while the remaining clathrates show unusual n–p transitions or sharp increases of thermopower at low temperatures. Estimations of the bandgaps as activation energy for resistivity dependences show an anomalous widening and then shrinking of the bandgap with increasing Cd-content.

Exceptionally high electronic mobility in defect-rich Eu2ZnSb2−xBix alloys

Alloying Eu2ZnSb2 with Bi on the Sb site leads to an increase in mobility while still lowering the lattice thermal conductivity.

Realization of interlayer ferromagnetic interaction in MnSb2Te4 toward the magnetic Weyl semimetal state.

Magnetic properties of MnSb2Te4 were examined through magnetic susceptibility, specific-heat, and neutron-diffraction measurements. As opposed to isostructural MnBi2Te4 with the antiferromagnetic ground state, MnSb2Te4 develops a spontaneous magnetization below 25 K. From our first-principles calculations on the material in a ferromagnetic state, the state could be interpreted as a type-II Weyl semimetal state with broken time-reversal symmetry. Detailed structural refinements using x-ray-diffraction and neutron-diffraction data reveal the presence of site mixing between Mn and Sb sites, leading to the ferrimagnetic ground state. With theoretical calculations, we found that the presence of site mixing plays an important role for the interlayer Mn-Mn ferromagnetic interactions.