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The prevalent global energy crisis calls for searching viable pathways for generating green hydrogen as an alternative energy resource. Dye‐sensitized photocatalytic water splitting is a feasible solution to produce green hydrogen. However, identifying suitable catalysts has been one of the bottlenecks in driving dye‐sensitized photocatalysis efficiently. In this work, a new class of electrocatalysts is reported based on the layered Weyl semimetals MIrTe4 (M = Nb, Ta) for the Eosin Y (EY)‐sensitized hydrogen evolution reaction (HER). NbIrTe4 and TaIrTe4 exhibit HER activities of ≈18 000 and 14 000 µmol g−1 respectively, after 10 h of irradiation with visible light. Time‐dependent UV‐Vis spectroscopy and high‐pressure liquid chromatography coupled with mass spectrometry analysis shed light on the reaction dynamics and enable a deeper understanding of the observed trend in hydrogen evolution rates for MIrTe4. MIrTe4 semimetals outperform transition metal‐based Weyl semimetals in terms of catalytic HER activity using EY as photosensitizer and triethanolamine as the sacrificial agent. It is hypothesized that the topology‐related band inversion in MIrTe4 Weyl semimetals promotes a high density of M d‐states near the Fermi level, driving their high catalytic performance. This study introduces a new class of layered Weyl semimetals as efficient catalysts, and provides perspectives for designing topology‐enhanced catalysts. [ABSTRACT FROM AUTHOR]

Here, we present lattice dynamics associated with the local chemical bonding hierarchy in Zintl compound TlInTe2, which cause intriguing phonon excitations and strongly suppress the lattice thermal conductivity to an ultralow value (0.46–0.31 W m−1 K−1) in the 300–673 K. We established an intrinsic rattling nature in TlInTe2 by studying the local structure and phonon vibrations using synchrotron X‐ray pair distribution function (PDF) (100–503 K) and inelastic neutron scattering (INS) (5–450 K), respectively. We showed that while 1D chain of covalently bonded InTe2n-n transport heat with Debye type phonon excitation, ionically bonded Tl rattles with a frequency ca. 30 cm−1 inside distorted Thompson cage formed by InTe2n-n. This highly anharmonic Tl rattling causes strong phonon scattering and consequently phonon lifetime reduces to ultralow value of ca. 0.66(6) ps, resulting in ultralow thermal conductivity in TlInTe2. [ABSTRACT FROM AUTHOR]

GeTe and its derivatives constituting Pb-free elements have been well known as potential thermoelectric materials for the last five decades, which offer paramount technological importance. The main constraint in the way of optimizing thermoelectric performance of GeTe is the high lattice thermal conductivity (κlat). Herein, we demonstrate low κlat (~0.7 W/m·K) and a significantly high thermoelectric figure of merit (ZT = 2.1 at 630 K) in the Sb-doped pseudoternary (GeTe)1-2x(GeSe)x(GeS)x system by two-step strategies. The (GeTe)1-2x(GeSe)x(GeS)x system provides an excellent podium to investigate competition between an entropy-driven solid solution and enthalpy-driven phase separation. In the first step, small concentrations of Se and S were substituted simultaneously in the position of Te in GeTe to reduce the κlat by phonon scattering due to mass fluctuations and point defects. When the Se/S concentration increases significantly, the system deviates from a solid solution, and phase separation of the GeS1-xSex (5-20 μm) precipitates in the GeTe1-xSex matrix occurs, which does not participate in phonon scattering. In the second stage, κlat of the optimized sample is further reduced to 0.7 W/m·K by Sb alloying and spark plasma sintering (SPS), which introduce additional phonon scattering centers such as excess solid solution point defects and grain boundaries. The low κlat in Sb-doped (GeTe)1-2x(GeSe)x(GeS)x is attributed to phonon scattering by entropically driven solid solution point defects rather than conventional endotaxial nanostructuring. As a consequence, the SPS-processed Ge0.9Sb0.1Te0.9Se0.05S0.05 sample exhibits a remarkably high ZT of 2.1 at 630 K, which is reproducible and stable over temperature cycles. Moreover, Sb-doped (GeTe)1-2x(GeSe)x(GeS)x exhibits significantly higher Vickers microhardness (mechanical stability) compared to that of pristine GeTe. [ABSTRACT FROM AUTHOR]

Waste heat sources are generally diffused and provide a range of temperatures rather than a particular temperature. Thus, thermoelectric waste heat to electricity conversion requires a high average thermoelectric figure of merit ( ZTavg) of materials over the entire working temperature along with a high peak thermoelectric figure of merit ( ZTmax). Herein an ultrahigh ZTavg of 1.4 for (GeTe)80(AgSbSe2)20 [TAGSSe-80, T=tellurium, A=antimony, G=germanium, S=silver, Se=selenium] is reported in the temperature range of 300-700 K, which is one of the highest values measured amongst the state-of-the-art Pb-free polycrystalline thermoelectric materials. Moreover, TAGSSe-80 exhibits a high ZTmax of 1.9 at 660 K, which is reversible and reproducible with respect to several heating-cooling cycles. The high thermoelectric performance of TAGSSe- x is attributed to extremely low lattice thermal conductivity ( κlat), which mainly arises due to extensive phonon scattering by hierarchical nano/meso-structures in the TAGSSe- x matrix. Addition of AgSbSe2 in GeTe results in κlat of ≈0.4 W mK−1 in the 300-700 K range, approaching to the theoretical minimum limit of lattice thermal conductivity ( κmin) of GeTe. Additionally, (GeTe)80(AgSbSe2)20 exhibits a higher Vickers microhardness (mechanical stability) value of ≈209 kgf mm−2 compared to the other state-of-the-art metal chalcogenides, making it an important material for thermoelectrics. [ABSTRACT FROM AUTHOR]

Waste heat sources are generally diffused and provide a range of temperatures rather than a particular temperature. Thus, thermoelectric waste heat to electricity conversion requires a high average thermoelectric figure of merit ( ZTavg) of materials over the entire working temperature along with a high peak thermoelectric figure of merit ( ZTmax). Herein an ultrahigh ZTavg of 1.4 for (GeTe)80(AgSbSe2)20 [TAGSSe-80, T=tellurium, A=antimony, G=germanium, S=silver, Se=selenium] is reported in the temperature range of 300-700 K, which is one of the highest values measured amongst the state-of-the-art Pb-free polycrystalline thermoelectric materials. Moreover, TAGSSe-80 exhibits a high ZTmax of 1.9 at 660 K, which is reversible and reproducible with respect to several heating-cooling cycles. The high thermoelectric performance of TAGSSe- x is attributed to extremely low lattice thermal conductivity ( κlat), which mainly arises due to extensive phonon scattering by hierarchical nano/meso-structures in the TAGSSe- x matrix. Addition of AgSbSe2 in GeTe results in κlat of ≈0.4 W mK−1 in the 300-700 K range, approaching to the theoretical minimum limit of lattice thermal conductivity ( κmin) of GeTe. Additionally, (GeTe)80(AgSbSe2)20 exhibits a higher Vickers microhardness (mechanical stability) value of ≈209 kgf mm−2 compared to the other state-of-the-art metal chalcogenides, making it an important material for thermoelectrics. [ABSTRACT FROM AUTHOR]

Spintronics exploiting pure spin current in ferromagnetic (FM)/heavy metals (HM) is a subject of intense research. Topological insulators having spin momentum locked surface states exhibit high spin–orbit coupling and thus possess a huge potential to replace the HM like Pt, Ta, W, etc. In this context, the spin pumping phenomenon in Bi2Se3/CoFeB bilayers has been investigated. Bi2Se3 thin films are fabricated by electron beam evaporation method on Si (100) substrate. In order to confirm the topological nature of Bi2Se3, low temperature magnetotransport measurement on a 30 nm thick Bi2Se3 film which shows 10% magnetoresistance (MR) at 1.5 K has been performed. A linear increase in MR with applied magnetic field indicates the presence of spin momentum‐locked surface states. A voltage has been measured at room temperature to quantify the spin pumping which is generated via inverse spin Hall effect (ISHE). For the separation of spin rectification effects mainly produced by the FM CoFeB layer, in plane angular dependence of the dc voltage with respect to applied magnetic field has been measured. Our analysis reveals that spin pumping induced ISHE is the dominant contribution in the measured voltage. Bi2Se3 thin film has been prepared by electron beam evaporation. Its magnetoresistance shows comparable value to Bi2Se3 films prepared by molecular beam epitaxy. Inverse spin Hall effect (ISHE) is observed predominantly due to spin pumping in Bi2Se3/CoFeB bilayers. Angle‐dependent measurements are performed to disentangle different spin rectification effects. [ABSTRACT FROM AUTHOR]

The article describes high thermoelectric performance in cadmium-doped polycrystalline silver antimony telluride caused by enhanced cationic ordering. Temperature-dependent electronic transport, transmission electron microscopy and first-principles density functional theory were used to show evidence of increased atomic ordering and the formation of nanoscale superstructures.

Thermoelectric (TE) energy conversion demands high performance crystalline inorganic solids that exhibit ultralow thermal conductivity, high mechanical stability, and good TE device properties. Pb-free germanium telluride (GeTe)-based material has recently attracted significant attention in TE power generation in mid temperatures, but pristine GeTe possesses significantly higher lattice thermal conductivity (κ latt ) compared to that of its theoretical minimum (κ min ) of ∼0.3 W/mK. Herein, we have demonstrated the reduction of κ latt of (GeTe) 1-2 x (SnSe) x (SnS) x very near to its κ min . The (GeTe) 1-2 x (SnSe) x (SnS) x system behaves as a coexistence of point-defect rich solid solution and phase separation. Initially, the addition of equimolar SnSe and SnS in the GeTe reduces the κ latt by effective phonon scattering because of the excess point defects and rich microstructures. In the second step, introduction of Sb-doping leads to additional phonon scattering centers and optimizes the p -type carrier concentration. Notably, 10 mol % Sb-doped (GeTe) 0.95 (SnSe) 0.025 (SnS) 0.025 exhibits ultralow κ latt of ∼0.30 W/mK at 300 K. Subsequently, 10 mol % Sb-doped (GeTe) 0.95 (SnSe) 0.025 (SnS) 0.025 exhibits a high TE figure of merit (zT) of ∼1.9 at 710 K. The high-performance sample exhibits a Vickers microhardness (mechanical stability) value of ∼194 H V that is significantly higher compared to the pristine GeTe and other state-of-the-art thermoelectric materials. Further, we have achieved a high output power, ∼150 mW for the temperature difference of 462 K, in single leg TE device based on 10 mol % Sb-doped (GeTe) 0.95 (SnSe) 0.025 (SnS) 0.025 .

Successful applications of a thermoelectric material require simultaneous development of compatible n- and p-type counterparts. While the thermoelectric performance of p-type GeTe has been improved tremendously in recent years, it has been a challenge to find a compatible n-type GeTe counterpart due to the prevalence of intrinsic Ge vacancies. Herein, we have shown that alloying of AgBiSe 2 with GeTe results in an intriguing evolution in its crystal and electronic structures, resulting in n-type thermoelectric properties. We have demonstrated that the ambient rhombohedral structure of pristine GeTe transforms into cubic phase in (GeTe) 100- x (AgBiSe 2 ) x for x ≥ 25, with concurrent change from its p-type electronic character to n-type character in electronic transport properties. Such change in structural and electronic properties is confirmed from the nonmonotonic variation of band gap, unit cell volume, electrical conductivity, and Seebeck coefficient, all of which show an inflection point around x ∼ 20, as well as from the temperature variations of synchrotron powder X-ray diffractions and differential scanning calorimetry. First-principles density functional theoretical (DFT) calculations explain that the shift toward n-type electronic character with increasing AgBiSe 2 concentration arises due to increasing contribution of Bi p orbitals in the conduction band edge of (GeTe) 100- x (AgBiSe 2 ) x . This cubic n-type phase has promising thermoelectric properties with a band gap of ∼0.25 eV and ultralow lattice thermal conductivity that ranges between 0.3 and 0.6 W/mK. Further, we have shown that (GeTe) 100- x (AgBiSe 2 ) x has promising thermoelectric performance in the mid-temperature range (400-500 K) with maximum thermoelectric figure of merit, zT , reaching ∼1.3 in p-type (GeTe) 80 (AgBiSe 2 ) 20 at 467 K and ∼0.6 in n-type (GeTe) 50 (AgBiSe 2 ) 50 at 500 K.

Ultrathin ferroelectric semiconductors with high charge carrier mobility are much coveted systems for the advancement of various electronic and optoelectronic devices. However, in traditional oxide ferroelectric insulators, the ferroelectric transition temperature decreases drastically with decreasing material thickness and ceases to exist below certain critical thickness owing to depolarizing fields. Herein, we show the emergence of an ordered ferroelectric ground state in ultrathin (∼2 nm) single crystalline nanosheets of Bi 2 O 2 Se at room temperature. Free-standing ferroelectric nanosheets, in which oppositely charged alternating layers are self-assembled together by electrostatic interactions, are synthesized by a simple, rapid, and scalable wet chemical procedure at room temperature. The existence of ferroelectricity in Bi 2 O 2 Se nanosheets is confirmed by dielectric measurements and piezoresponse force spectroscopy. The spontaneous orthorhombic distortion in the ultrathin nanosheets breaks the local inversion symmetry, thereby resulting in ferroelectricity. The local structural distortion and the formation of spontaneous dipole moment were directly probed by atomic resolution scanning transmission electron microscopy and density functional theory calculations.