Sb Sites Research Articles

Enhanced High-Temperature Thermoelectric Performance in Te-Doped Electronegative Element-Filled Skutterudites via Suppressing Bipolar Effects and Enhanced Phonon Scattering.

CoSb3-based skutterudites have great potential as midtemperature thermoelectric (TE) materials due to their low cost and excellent electrical and mechanical properties. Their application, however, is limited by the high thermal conductivity and the degradation of TE performance at elevated temperatures, attributed to the adverse effects of bipolar diffusion. Herein, a series of SeyCo4Sb12-xTex compounds were successfully synthesized by combining a solid-state reaction and spark plasma sintering techniques to mitigate these challenges. It was found that doping Te at the Sb sites effectively enhanced the carrier concentration and suppressed the bipolar effect to obtain a superior power factor of ∼43 μW cm-1 K-2. Furthermore, due to the low resonant frequency of Se, filling voids of CoSb3 with Se achieved a low lattice thermal conductivity of 1.55 W m-1 K-1. Nevertheless, Se filling introduced additional holes, reducing the carrier concentration without a significant detriment of the carrier mobility. As a result, a maximum figure of merit of 1.23 was achieved for Se0.1Co4Sb11.55Te0.45 at 773 K. This work provides a valuable guidance for selecting appropriate filling and doping components to achieve synergistic optimization of the acoustics and electronics of CoSb3-based skutterudites.

Lazerckerite, Ag3.75Pb4.5(Sb7.75Bi4)S24, from Kutná Hora, Czech Republic: a new Sb–Bi member of the andorite branch of the lillianite homologous series

Abstract. Lazerckerite, ideally Ag3.75Pb4.5(Sb7.75Bi4)S24, is a new mineral species found in medieval mine dumps of the historic Ag–Pb–Zn Kutná Hora ore district, Czech Republic. The mineral is associated with other Sb–Bi lillianite homologues (terrywallaceite, gustavite, holubite) and Ag,Bi-bearing galena, most frequently as grain aggregates and replacement rims of earlier Ag–Pb–Bi minerals, growing together in aggregates of up to 0.6×0.3 mm. Lazerckerite is opaque, is steel grey in colour, and has a metallic lustre; the calculated density is 5.920 g cm−3. In reflected light lazerckerite is greyish white, and bireflectance and pleochroism are weak with grey tints. Anisotropy is weak to moderate with grey to bluish-grey rotation tints. Internal reflections are not observed. Electron microprobe analyses yielded the empirical formula, based on 44 apfu, (Ag3.61Cu0.04)Σ3.65(Pb4.55Fe0.01Cd0.01)Σ4.57(Sb7.87Bi3.75)Σ11.62(S24.15Se0.01)Σ24.16. Its unit cell parameters are a=13.2083(9), b=19.4595(8), c=8.4048(13), β=90.032(7)°, V=2160.3(4) Å3, space group P21/c, and Z=2. The structure of lazerckerite contains two Pb sites (Pb1 and Pb2) in bicapped trigonal prismatic coordination, 8 independent octahedral sites, and 13 distinct sulfur positions. Four of the octahedral sites are mixed (Sb,Bi) and (Bi,Sb) sites, one is a mixed (Ag,Bi) site, and one is a mixed (Sb,Pb) site. The new mineral belongs to the andorite branch of the lillianite homologous series with N=4 and is a new addition to the group of Sb–Bi mixed members of the series. Lazerckerite is defined as a lillianite homologue with the three following requirements: N=4, L (Ag++ (Bi3+, Sb3+) ↔ 2 Pb2+ substitution) ≈ 90 %–95 %, and approximately one-third of atom percentage of antimony is replaced by bismuth (Bi/(Bi+Sb) ≈ 0.30–0.38). The new mineral has been approved by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA 2022-113) and named after Lazarus Ercker, the supreme Royal Bergmeister of the Kingdom of Bohemia and the Master of Prague Mint.

Probing the contribution of bismuth on electronic transport and phonon scattering properties of Mg3Sb2-xBix solid solutions

In this work, first-principles calculations have been used to investigate the electronic structure, phonon scattering, and Debye temperature of Mg3Sb2-xBix alloys. The electronic transport properties were predicted by solving the Boltzmann equations. Additionally, thermoelectric properties of alloys with corresponding compositions prepared using directional solidification were analyzed and compared with the predicted results. The research findings reveal that the increase in Bi content is accompanied by an increase in carrier concentration and mobility, and a decrease in carrier effective mass. The Mg3Sb1.5Bi0.5 alloy showed the highest power factor value of 0.49 mWm−1K−2 due to the synergistic effect between the electrical conductivity and the Seebeck coefficient. As the Bi atoms replace Sb sites, the scattering rates of low-frequency phonons become stronger, significantly reducing the lattice thermal conductivity. The Mg3Sb0.5Bi1.5 alloy reaches the lowest thermal conductivity, especially in the low and medium temperature range. Mg3Sb1.5Bi0.5 alloy provides the maximum ZT value of 0.29 at 630 K. This study systematically analyzes the impact of Bi on electronic transport and phonon scattering in Mg3Sb2-xBix alloys，and extensively discusses the dependence of thermoelectric performance parameters on Bi content. This work also provides a theoretical reference for the subsequent research on doping modification of Mg3Sb2-xBix alloys.

The Faradaic-Induced hybrid capacitive engine enables high-performance selective defluorination via capacitive deionization

Fluoride (F-) contamination has become a pressing environmental concern owing to its extensive origins and severe toxicity. Capacitive deionization (CDI) emerges as a promising technique for efficient defluorination, with the development of electrode materials being pivotal to its efficiency. Herein, we present a novel design of Sb-decorated N-rich carbon composites (SNTPCs) for the formation of a hybrid capacitive engine that integrates Faradaic-induced pseudocapacitance and electrical double layer capacitance, enabling efficient F- electrosorption. This approach features a distinctive N-rich carbonaceous laminar framework that not only guarantees rapid ion diffusion and electron transfer but also provides a dense electrical double layer for F- storage. The Sb sites are electrically stimulated to release the intrinsic affinity with F-, forming the Faradaic Sb-F bonds. The SNTPC2 electrode exhibits the exceptional saturation removal capability and dynamic electrosorption capacity for defluorination, reaching 178.58 and 34.77 mg F/g at 1.2 V respectively, which exceeds most reported F- capture electrodes. It also demonstrates excellent selectivity towards F- in complex conditions and exhibits effectiveness across a wide range of pH values. Additionally, the utilized electrode performs outstanding regeneration performance after 20 consecutive cycles. This study provides innovative perspectives for the effective elimination of fluoride pollution in aquatic environments.

Accelerated Proton Transfer in Asymmetric Active Units for Sustainable Acidic Oxygen Evolution Reaction.

The poor durability of Ru-based catalysts limits the practical application in proton exchange membrane water electrolysis (PEMWE). Here, we report that the asymmetric active units in Ru1-xMxO2 (M = Sb, In, and Sn) binary solid solution oxides are constructed by introducing acid-resistant p-block metal sites, breaking the activity and stability limitations of RuO2 in acidic oxygen evolution reaction (OER). Constructing highly asymmetric Ru-O-Sb units with a strong electron delocalization effect significantly shortens the spatial distance between Ru and Sb sites, improving the bonding strength of the overall structure. The unique two-electron redox couples at Sb sites in asymmetric active units trigger additional chemical steps at different OER stages, facilitating continuous proton transfer. The optimized Ru0.8Sb0.2O2 solid solution requires a superlow overpotential of 160 mV at 10 mA cm-2 and a record-breaking stability of 1100 h in an acidic electrolyte. Notably, the scale-prepared Ru0.8Sb0.2O2 achieves efficient PEMWE performance under industrial conditions. General mechanism analysis shows that the enhanced proton transport in the asymmetric Ru-O-M unit provides a new working pathway for acidic OER, breaking the scaling relationship without sacrificing stability.

Insights into enhanced thermoelectric performance of the n-type Mg3Sb2-based materials by amphoteric Al doping

Doping has the potential to alter the levels of anharmonicity in compounds by attenuating bonding strength. In this study, we explore the efficacy of amphoteric Al doping for stimulating anharmonicity in n-type Mg3.25AlxSb1.48Bi0.48Te0.04 to attain enhanced phonon scattering and thermoelectric performance. First-principles calculations and experimental data reveal the occupation of both Sb and Mg2 sites by amphoteric Al atoms in the anionic framework of Mg3.25AlxSb1.48Bi0.48Te0.04. A marginal variation in both carrier concentration and mobility sustains the high power factor without affecting the Seebeck coefficient, implying amphoteric doping induced charge compensation. While phonon velocity, Grüneisen parameter, and crystal orbital Hamilton population calculations results indicate that phonon softening and bond weakening are realized via Al doping, leading to an enhanced lattice anharmonicity and a reduced lattice thermal conductivity. A remarkable enhancement ∼16% in the peak figure of merit ZTpeak and the average ZTavg, was attained for the x = 0.015 sample, when compared with the un-doped sample. Hence, the amphoteric doping can serve as an effective means to optimize ZT values by decoupling the intertwined thermoelectric transport properties.

Molecular dissociation of nitric oxide (NO) on VO2(010) surface : A DFT study including vdW forces

The adsorption and coadsorption of O and N atomic species, as well as the dissociation of NO molecule on VO2(010) surface have been studied using the density functional theory (DFT) with GGA-PBE as the exchange–correlation, including van der Waals (vdW) corrections of the form PBE+vdW-DF2. We found that the short-bridge (sb) site is the energetically most stable for both N and O atoms. The inclusion of PBE+vdW-DF2 corrections does not change the preferred adsorption site, however it reduces the value of the adsorption energy relative to ordinary GGA-PBE functional. Also, while the GGA-PBE functional results in finite magnetization on the O and N atoms when adsorbed on the VO2 surface, the inclusion of the vdW forces results in zero magnetization of the atoms. In addition, our Löwdin charge transfer analysis shows electron transfer from the VO2(010) surface to the O atom, which is further supported by an accumulation of charge density around the O atom as well as the charge depletion from the V surface atoms. At a lower coverage θ= 0.25 ML, the N atom behaves like a charge acceptor, that is, electrons are transferred from the VO2 surface to it. At a higher coverage θ= 0.50 ML and 0.75 ML, the N atom behaves like a charge donor, i.e., there is a transfer of electronic charges to the VO2 surface. We emphasize that charge transfer between the adsorbate (O and N) and the surface establishes adsorbate-surface bonding which enhances the stability of the adsorbate. Furthermore, our nudged elastic band calculations (NEB) for determining the minimum energy path (MEP) and activation barrier energy (Ea) for NO dissociation into N and O atoms show Ea= 2.18 eV (1.78 eV) as obtained using the GGA-PBE (PBE+vdW-DF2) functionals. Regarding potential application, this study thus contributes to reducing the amount and harmful effect of NO gas in the atmosphere.

Tuning of thermoelectric performance by modulating vibrational properties in Ni-doped Sb2Te3

Sb2Te3, a binary chalcogenide-based 3D topological insulator, attracts significant attention for its exceptional thermoelectric performance. We report the vibrational properties of magnetically doped Sb2Te3 thermoelectric material. Ni doping induces defect/disorder in the system and plays a positive role in engineering the thermoelectric properties through tuning the vibrational phonon modes. Synchrotron powder x-ray diffraction study confirms good crystalline quality and single-phase nature of the synthesized samples. The change in structural parameters, including B iso and strain, further corroborate with structural disorder. Detailed modification of phonon modes with doping and temperature variation is analysed from temperature-dependent Raman spectroscopic measurement. Compressive lattice strain is observed from the blue shift of Raman peaks owing to Ni incorporation in Sb site. An attempt is made to extract the lattice thermal conductivity from total thermal conductivity estimated through optothermal Raman studies. Hall concentration data support the change in temperature-dependent resistivity and thermopower. Remarkable increase in thermopower is observed after Ni doping. Simulation of the Pisarenko model, indicating the convergence of the valence band, explains the observed enhancement of thermopower in Sb2−x Ni x Te3. The energy gap between the light and heavy valence band at Γ point is found to be 30 meV (for Sb2Te3), which is reduced to 3 meV (in Sb1.98Ni0.02Te3). A significant increase in thermoelectric power factor is obtained from 715 μWm−1K−2 for pristine Sb2Te3 to 2415 μWm−1K−2 for Ni-doped Sb2Te3 sample. Finally, the thermoelectric figure of merit, ZT is found to increase by four times in Sb1.98Ni0.02Te3 than that of its pristine counterpart.

Markwelchite, TlPbSbS3, a new Tl–Pb sulfosalt from the hydrothermal deposit of Jas Roux, Hautes-Alpes, France

AbstractMarkwelchite, ideally TlPbSbS3, is a new mineral from the hydrothermal deposit of Jas Roux, Hautes-Alpes, France. It occurs as a black anhedral crystal associated closely with protochabournéite. Microhardness measurements (VHN15) gave a mean value of 197 kg/mm2 corresponding to a Mohs hardness of ~3–4. In plane-polarised incident light, markwelchite is grey in colour. Under crossed polars, it is distinctly anisotropic with greyish white to bluish rotation tints, with bright red internal reflections. Reflectance percentages (Rmin and Rmax) are: 28.5, 31.5 (471.1 nm); 28.3, 30.7 (548.3 nm); 27.9, 30.3 (586.6 nm); and 27.6, 29.8 (652.3 nm). The mean of 5 electron microprobe spot analyses gave Tl 34.67(45), Pb 31.86(25), Sb 15.06(15), As 2.37(5), S 15.35(20), total 99.31 wt.%, corresponding, on the basis of a total of 6 atoms per formula unit and structural results, to Tl1.063Pb0.964(Sb0.775As0.198)Σ0.973S3.000. Single-crystal X-ray diffraction studies revealed that markwelchite is isotypic with richardsollyite, TlPbAsS3. It is monoclinic, space group P21/c, with the following unit-cell parameters: a = 8.9144(3), b = 8.4513(3), c = 8.6511(3) Å, β = 108.723(4)°, V = 617.27(4) Å3 and Z = 4. The five strongest observed powder-diffraction lines [d in Å (Irel)(hkl)] are: 3.88 (100)($\bar{2}$11); 3.78 (90)(210); 3.29 (90)(102); 2.73 (85)($\bar{1}$13); and 2.93 (75)(022). The crystal structure can be described as formed by (100) [Me2(SbS3)]– layers sandwiching the Me1+ cations. The Me1 site has a seven-fold coordination, whereas the Me2 site has an 6+2 coordination corresponding to a distorted, bicapped trigonal prismatic coordination, and the Sb site displays a trigonal pyramidal coordination with three S atoms and Sb at the apex.The name markwelchite honours Dr Mark D. Welch of the Natural History Museum, London, UK.The new mineral has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2024–001). A discussion on the relationships between markwelchite and synthetic TlPbSbS3 is also provided.

Elucidation of heavy metal content, phenolic profiles, and antioxidant activities of kale (Brassica oleracea L. var. acephala) and arugula (Brassica eruca L.) grown in urban gardens in Istanbul.

This study was conducted to evaluate the effect of two distances: close (0-10m) and far (60m) from the heavy traffic roadside, at three different cultivation sites (MS: Mevlanakapi-Silivrikapi, SB: Silivrikapi-Belgradkapi, and BY: Belgradkapi-Yedikule kapi) along the road line. First, the phenolic compounds, antioxidant activity, and physicochemical properties in kale and arugula vegetables were examined. Second, heavy metal concentrations in vegetables, soil, and irrigated water were investigated. In both vegetables, the highest total phenolic content was detected in samples obtained from far distance in SB site (3880.3mg/kg) for kale and in BY site (1459.9mg/kg) for arugula, whereas the lowest content was found at the close distance in MS site for both kale (448.5mg/kg) and arugula (586.4mg/kg). The antioxidant activity values [mg Trolox/kg (dw)] ranged from 366.74 to 586.10 and 2349.00 to 3757.4 for kale and from 520.00 to 945.60 and 3323.00 to 5814.70 for arugula in 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) and 2,2-diphenyl-1-picrylhydrazyl methods, respectively. The levels of Cd and Hg in kale and arugula and Fe content in arugula exceeded FAO/WHO permissible limits, making them unsafe for human consumption. Meanwhile, the Pb content in kale and arugula and Fe content in kale were observed to be within acceptable limits set by FAO/WHO. In the irrigated water, the Pb value was below the permissible limit, whereas the Cd value was above it and no Hg and Fe were detected. In the soil samples, the Pb and Fe values were below the limit, whereas the Cd and Hg values were higher.

Suppressed Lone Pair Electrons Explain Unconventional Rise of Lattice Thermal Conductivity in Defective Crystalline Solids.

Manipulating thermal properties of materials can be interpreted as the control of how vibrations of atoms (known as phonons) scatter in a crystal lattice. Compared to a perfect crystal, crystalline solids with defects are expected to have shorter phonon mean free paths caused by point defect scattering, leading to lower lattice thermal conductivities than those without defects. While this is true in many cases, alloying can increase the phonon mean free path in the Cd-doped AgSnSbSe3 system to increase the lattice thermal conductivity from 0.65 to 1.05Wm-1K-1 by replacing 18% of the Sb sites with Cd. It is found that the presence of lone pair electrons leads to the off-centering of cations from the centrosymmetric position of a cubic lattice. X-ray pair distribution function analysis reveals that this structural distortion is relieved when the electronic configuration of the dopant element cannot produce lone pair electrons. Furthermore, a decrease in the Grüneisen parameter with doping is experimentally confirmed, establishing a relationship between the stereochemical activity of lone pair electrons and the lattice anharmonicity. The observed "harmonic" behavior with doping suggests that lone pair electrons must be preserved to effectively suppress phonon transport in these systems.

Enhanced Thermoelectric Performance in Ca-doped AgSbTe2

Thermoelectric materials play a crucial role in applications such as recovering waste heat and refrigeration. We report a thermoelectric figure of merit (zT) of 1.17 at 623 K for AgSb1-xCaxTe2, representing a 31% enhancement compared to pristine AgSbTe2. The improved thermoelectric performance arises from enhancements in both the power factor and lattice thermal conductivity. Dopant substitution of element Ca at the Sb site in AgSbTe2 suppresses the formation of Ag2Te and increases the concentration of p-type charge carriers, leading to enhanced electrical transport properties. Additionally, Ca doping introduces solid solution point defects that enhance phonon scattering, consequently reducing the lattice thermal conductivity of the sample. This work demonstrates that a doping effectively modulates the electrical and thermal transport properties of AgSbTe2, thereby realizing improvements in thermoelectric performance.

Ni active sites isolated by antimony toward enhanced propyne semi‐hydrogenation

AbstractRegulating Ni active sites toward the formation of target product is of great importance for designing high‐performance cost‐effective catalysts for catalytic semi‐hydrogenations but remains challenging. Herein, we report the fabrication of NiSb intermetallic catalyst via structural transformation from a layered double hydroxides precursor for boosting propyne semi‐hydrogenation. Systematic characterizations, including x‐ray diffraction, atomic‐resolution electron microscopy, and x‐ray absorption spectroscopy, provide evidence for the formation of P63/mmc NiSb intermetallic phase in the synthesized NiSb catalyst. The host Ni active sites are demonstrated to be isolated by the high‐electronegativity p‐block guest Sb sites, which deliver remarkably high selectivity to target propene, that is, up to propene selectivity of 96% at nearly full propyne conversion. Temperature‐programmed surface reaction and temperature‐programmed desorption measurements combined with theoretical calculations unravel that the excellent selectivity originates from kinetically more favorable desorption of propene than its hydrogenation to propane on the regulated Ni active sites.

Antimony-Based Halide Perovskite Nanoparticles as Lead-Free Photocatalysts for Controlled Radical Polymerization.

Metal halide perovskites have emerged as versatile photocatalysts to convert solar energy for chemical processes. Perovskite photocatalyzed polymerization draws special attention due to its straightforward synthesis process and the ability to create advanced perovskite-polymer nanocomposites. Herein, this work employs Cs3Sb2Br9 perovskite nanoparticles (NPs) as a lead-free photocatalyst for light-controlled atom transfer radical polymerization (ATRP). Cs3Sb2Br9 NPs exhibit high reduction potential and interact with electronegative bromide initiator with Lewis acid Sb sites, enabling efficient photoinduced reduction of initiators and controlled polymerization under blue light irradiation. Methacrylate monomers with various functional groups are successfully polymerized, and the resulting polymer showcased a dispersity (Đ) as small as 1.27. The living nature of polymerization is confirmed by high chain end fidelity and kinetic studies. Moreover, Cs3Sb2Br9 NPs serve as heterogeneous photocatalysts, demonstrating recyclability and reusability for up to four cycles. This work presents a promising approach to overcome the limitations of lead-based perovskites in photoinduced controlled radical polymerization, offering a sustainable and efficient alternative for the synthesis of well-defined polymeric materials.

Experimental nuclear quadrupole resonance and computational study of the structurally refined topological semimetal TaSb2

The local electric field gradients and magnetic dynamics of TaSb2 have been studied using Sb121, Sb123, and Ta181 nuclear quadrupole resonance (NQR) with density functional theory (DFT) calculations using XRD-determined crystal structures. By measuring all structurally expected 13 NQR lines, the nuclear quadrupole coupling constant (νQ) and asymmetric parameter (η) for Ta, Sb(1), and Sb(2) sites were obtained. These values are all in good agreement with the presented DFT calculations. Principal axes of the electric field gradients was determined for a single-crystal sample by measuring the angular dependencies of NMR frequency under a weak magnetic field. The unusual temperature dependence of η(T) of Sb(2) hints at the suppressed thermal expansion along the a axis. Spin-lattice relaxation rate (1/T1T) measurements reveal an activated-type behavior and an upturn below 30 K. Neither the low-temperature upturn nor the high-temperature activation-type behaviors are reproduced by the calculated 1/T1T based on the calculated density of states (DOS). On the other hand, the agreement between the calculated DOS and specific heat measurements indicates that the band renormalization is small. This fact indicates that TaSb2 deviates from the simple semimetal scenario, and magnetic excitations are not captured by Fermi liquid theory. Published by the American Physical Society 2024

Band Engineering Through Pb-Doping of Nanocrystal Building Blocks to Enhance Thermoelectric Performance in Cu3SbSe4.

Developing cost-effective and high-performance thermoelectric (TE) materials to assemble efficient TE devices presents a multitude of challenges and opportunities. Cu3SbSe4 is a promising p-type TE material based on relatively earth abundant elements. However, the challenge lies in its poor electrical conductivity. Herein, an efficient and scalable solution-based approach is developed to synthesize high-quality Cu3SbSe4 nanocrystals doped with Pb at the Sb site. After ligand displacement and annealing treatments, the dried powders are consolidated into dense pellets, and their TE properties are investigated. Pb doping effectively increases the charge carrier concentration, resulting in a significant increase in electrical conductivity, while the Seebeck coefficients remain consistently high. The calculated band structure shows that Pb doping induces band convergence, thereby increasing the effective mass. Furthermore, the large ionic radius of Pb2+ results in the generation of additional point and plane defects and interphases, dramatically enhancing phonon scattering, which significantly decreases the lattice thermal conductivity at high temperatures. Overall, a maximum figure of merit (zTmax) ≈ 0.85 at 653 K is obtained in Cu3Sb0.97Pb0.03Se4. This represents a 1.6-fold increase compared to the undoped sample and exceeds most doped Cu3SbSe4-based materials produced by solid-state, demonstrating advantages of versatility and cost-effectiveness using a solution-based technology.

Antisite-Defects Control of Magnetic Properties in MnSb2Te4.

The intrinsic magnetic topological materials Mn(Sb/Bi)2n+2Te3n+4 have attracted extensive attention due to their topological quantum properties. Although, the Mn-Sb/Bi antisite defects have been frequently reported to exert significant influences on both magnetism and band topology, their formation mechanism and the methods to manipulate their distribution and concentration remain elusive. Here, we present MnSb2Te4 as a typical example and demonstrate that Mn-Sb antisite defects and magnetism can be tuned by controlling the crystal growth conditions. The cooling rate is identified as the primary key parameter. Magnetization and chemical analysis demonstrate that a slower cooling rate would lead to a higher Mn concentration, a higher magnetic transition temperature, and a higher saturation moment. Further analysis indicates that the Mn content at the original Mn site (MnMn, 3a site) varies more significantly with the cooling rate than the Mn content at the Sb site (MnSb, 6c site). Based on experimental observations, magnetic phase diagrams regarding MnMn and MnSb concentrations are constructed. With the assistance of first-principles calculations, it is demonstrated that the Mn-Sb mixing states primarily result from the mixing entropy and the growth kinetics. The present findings offer valuable insights into defects engineering for preparation of two-dimensional quantum materials.

Transport and electrical properties of cryogenic thermoelectric FeSb2: the effect of isoelectronic and hole doping

Thermoelectric materials operating at cryogenic temperatures are in high demand for efficient cooling and power generation in applications ranging from superconductors to quantum computing. The narrow band-gap semiconductor FeSb2, known for its colossal Seebeck coefficient, holds promise for such applications, provided its thermal conductivity value can be reduced. This study investigates the impact of isoelectronic substitution (Bi) and hole doping (Pb) at the Sb site on the transport properties of FeSb2, with a particular focus on thermal conductivity (κ). Polycrystalline FeSb2 powder, along with Bi- and Pb-doped samples, were synthesized using a simple co-precipitation approach, followed by thermal treatment in an H2 atmosphere. XRD and SEM analysis confirms the formation of the desired phase pre- and post-consolidation using spark plasma sintering. The consolidation process resulted in a high compaction density and the formation of submicrometer-sized grains, as substantiated by electron backscattered diffraction analysis. Substituting 1% of Bi and Pb at the Sb site successfully suppressed the thermal conductivity (κ) from ∼15 W (m·K)−1 in pure FeSb2 to ∼10 and ∼8.7 W (m·K)−1, respectively. Importantly, resistivity measurements revealed a metal-to-insulator transition at around 6.5 K in undoped FeSb2 and isoelectronically Bi-substituted FeSb2, suggesting the existence of metallic surface states and provides valuable evidence for the perplexing topological behavior exhibited by FeSb2.

ScFeSb3S7: Synthesis and characterization of a new mixed-metal sulfide

Mixed transition metal chalcogenides are pursued for various semiconducting applications. Herein, we report a new mixed transition metal containing quaternary chalcogenide, ScFeSb3S7, which has been prepared by a high-temperature reaction of elements at 1173 K. A single-crystal X-ray diffraction study shows that the monoclinic ScFeSb3S7 structure (space group: C2/m) is disordered with a mixed Sc and Sb site. The lattice parameters of the structure are a = 12.439(5) Å, b = 3.7938(13) Å, c = 11.604(4) Å, β = 106.095(10)°, and Z = 2. The seven unique crystallographic sites of the structure are occupied, which include Fe1, Sb1, mixed Sc1/Sb2, and four S sites. Each of the Fe1 and Sc1/Sb2 atoms is coordinated with six neighboring sulfur atoms in an octahedral fashion, whereas the Sb1 atom occupies the center of a distorted square pyramidal geometry of the S atoms. The (Sc1/Sb2)S6, FeS6, and SbS5 units are the primary building blocks of the ScFeSb3S7 structure. Both resistivity and optical absorption [Eg = 1.5(1) eV] studies confirm that the ScFeSb3S7 is a semiconductor. A thermal conductivity (ktot) study shows that the polycrystalline sample is a poor thermal conductor with an ultralow ktot value of ∼0.30 W/mK at 773 K. DFT studies also indicate the semiconducting nature of the ScFeSb3S7. The COHP analyses suggest stronger bonding interactions between Sb and S than the Sc/Fe with the S atoms.

Enhancement on thermoelectric performance by Ti doping and vacancies

Due to the exceptionally low lattice thermal conductivity, AgSbTe2 has emerged as a promising thermoelectric material. However, unlike other IV-VI compounds, most reported AgSbTe2 samples exhibit relatively poor electrical performance due to low carrier concentration. Herein, an unusually strategy of introducing dopants and vacancies on the same site of Sb is adopted, which significantly improves the electrical performance of AgSbTe2. It is found that Ti doping on Sb site can increase the carrier concentration and promote band convergence, based on which the introduction of Sb vacancy further enlarges the carrier concentration to approach the optimal value without affecting the carrier mobility. Consequently, an excellent average power factor of 1.4 mW m−1K−2 is achieved in AgSb0.94 Ti0.05Te2 from 323 K to 623 K. Combining with reduced thermal conductivity due to strengthened phonon scattering induced by the abundant lattice defects, a peak zT of 1.8 and a high average zT of 1.3 are attained. These results provide some new insights for improving the thermoelectric performance of AgSbTe2 based compounds.