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Dense ceramics of the itinerant ferromagnet CoS2 have been prepared by the spark plasma sintering technique. The structural study confirms a cubic unit-cell for CoS2 with a = 5.539(6)Å ([formula]). Scanning and transmission electron microscopy reveal the existence of sulfur deficient regions of composition 'Co2S3' with a structure compatible to that of CoS2 where 0.5 S atom are missing in one out of two successive layers along the b direction. The volume of these regions estimated to be less than 1% is explained by possible S losses from the surface during the sintering. The physical properties measurements show a high TC (122 K), large saturated magnetization (0.88 μB/f.u.), with a ∼100% magnetoresistance at 5 K in 9 T. Also, the value of the residual resistivity ratio, ρ300 K/ρ5 K = 45, between those of crystal and conventional ceramics, attest for both good compacity and grain connectivity. Interestingly, the Seebeck coefficient exhibits negative values reaching S = -47.5 μV K-1 at 675 K and below TC, S can be fitted by a diffusion model with a magnon term related to the ferromagnetism. A large power factor (S2/ρ) of 1 mW m-1 K-2 is obtained over a broad T range but the too high thermal conductivity (κ675 K ∼ 8.7 W K-1 m-1) is a limiting physical parameter to use CoS2 ceramics in thermoelectric devices. [ABSTRACT FROM AUTHOR]

We report on coupled changes in the dielectric permittivity and the magnetic susceptibility in the insulating antiferromagnet Ba2FeSbSe5. The real part of the dielectric permittivity (ε′) and the thermal conductivity (κ) shows pronounced anomalies at the Néel temperature (TN). Our findings show that there is a weak coupling between electric dipoles and magnetic spins, which is mediated by spin-lattice coupling possibly through exchange striction effects. [ABSTRACT FROM AUTHOR]

We report on coupled changes in the dielectric permittivity and the magnetic susceptibility in the insulating antiferromagnet Ba2FeSbSe5. The real part of the dielectric permittivity (ε′) and the thermal conductivity (κ) shows pronounced anomalies at the Néel temperature (TN). Our findings show that there is a weak coupling between electric dipoles and magnetic spins, which is mediated by spin-lattice coupling possibly through exchange striction effects. [ABSTRACT FROM AUTHOR]

U34Fe4-xGe33 is prepared by arc melting of the elements in the molar ratio U:Fe:Ge = 9:1:10. [ABSTRACT FROM AUTHOR]

The new title compound is obtained from a stoichiometric melt of the elements. [ABSTRACT FROM AUTHOR]

The novel quaternary compound Rb 0.2 Ba 0.4 Cr 5 Se 8 was synthesized and characterized in both single crystal and polycrystalline forms. Crystallizing in the monoclinic crystal system (space group C 2/ m , cell parameters a = 18.7071(4) Å, b = 3.6030(1) Å, c = 8.9637(3) Å, β = 104.494(2)°) and isostructural to pseudo-hollandite compounds, it features mixed Rb and Ba occupancy within its one-dimensional channels. High-temperature X-ray diffraction revealed no decomposition up to 973 K, and the thermal expansion coefficient at 300 K was determined to be 2.6(1)·10 -5 K -1 . Spin-polarized density functional theory (DFT) calculations showed that the density of states for Rb 0.2 Ba 0.4 Cr 5 Se 8 is more polarized than that of Ba 0.5 Cr 5 Se 8 , resulting in a higher Seebeck coefficient, which was experimentally confirmed to reach a peak value of 400 μV·K -1 at 620 K. Resistivity measurements indicated a degenerate semiconducting behavior below 550 K, with a resistivity peak of 100 mΩ·cm at that temperature, leading to a maximum power factor of 0.21 mW·m -1 ·K -2 . Thermal conductivity measurements indicated low values around 0.8 W·m -1 ·K -1 in the 300-900 K range, resulting in a thermoelectric figure of merit of 0.22 at 873 K. Decorrelated transport properties observed in this double-inserted pseudo-hollandite compound make Rb 0.2 Ba 0.4 Cr 5 Se 8 a good example of beneficial synergistic effects for higher thermoelectric performance.

This article presents a comprehensive study on the synthesis and structural and thermal conductivity properties of cesium-inserted chromium tellurides of formula Cs x Cr 5 Te 8 . Single crystals of three different compositions ( x = 0.73, 0.91, and 0.97) were successfully synthesized and suggested the existence of a solid solution in the range 0.73 < x < 1. Through a detailed single-crystal characterization, the complete structure of these compounds is determined, revealing a distinct B -type hollandite-like structural form derived from the hollandite structure, in contrast to the more commonly observed A -type pseudo-hollandite in AM 5 X 8 -type chalcogenides (A = cation, M = transition metal, and X = chalcogen). Periodic density functional theory calculations predict the Cs 0.73 Cr 5 Te 8 composition as the most stable, with a metallic conductive behavior. The thermal conductivity of bulk Cs x Cr 5 Te 8 samples is measured to be 1.4 W m -1 K -1 at 300 K and increases with temperature up to 2 W m -1 K -1 at 673 K.

The high-performance defect-rich MoS 2 dominated by sulfur vacancies as well as Mo-rich environments have been extensively studied in many fields, such as nitrogen reduction reactions, hydrogen evolution reactions, as well as sensing devices for NH 3 , which are attributed to the under-coordinated Mo atoms playing a significant role as catalytic sites in the defect area. In this study, the Mo cluster-MoS 2 composite was creatively synthesized through a one-step sulfurization process via H 2 /H 2 S gas flow. The Mo 6 cluster iodides (MIs) coated on the fluorine-doped tin oxide (FTO) glass substrate via the electrophoretic deposition method (i.e., MI@FTO) were used as a precursor to form a thin-film nanocomposite. Investigations into the structure, reaction mechanism, and NH 3 gas sensing performance were carried out in detail. The results indicated that during the gas flowing, the decomposed Mo 6 cluster iodides played the role of template and precursor, forming complicated Mo cluster compounds and eventually producing MoS 2 . These Mo cluster-MoS 2 thin-film nanocomposites were fabricated and applied as gas sensors for the first time. It turns out that after the sulfurization process, the response of MI@FTO for NH 3 gas increased three times while showing conversion from p-type to n-type semiconductor, which enhances their possibilities for future device applications., Competing Interests: The authors declare no conflict of interest.

Machine learning (ML) methods extract statistical relationships between inputs and results. When the inputs are solid-state crystal structures, structure-property relationships can be obtained. In this work, we investigate whether a simple neural network is able to learn the 3d orbital occupations for the transition-metal (TM) centers in crystalline inorganic solid-state compounds using only the local structure around the transition-metal centers described by rotationally invariant fingerprints based on spherical harmonics and one-hot elemental encoding. A multilayer neural network trained on density functional theory (DFT) results of about 1800 samples was developed and showed good performance in predicting the TM orbital occupations (for both spin channels). We study in detail how the local structure affects the predictions of the local properties and how they provide physical insights for the design of a future machine learning model for materials chemistry. The proposed ML method is illustrated in practical application by predicting local magnetic moments of the transition-metal atoms in a full set of inorganic structures with large unit cells. Although less accurate compared to the experimental data, the ML results compared well with the DFT results, suggesting the feasibility of electronic property prediction based only on structure input.

In the frame of the nanoarchitectonic concept, the objective of this study was to develop simple and easy methods to ensure the preparation of polymorphic HfO2 thin film materials (<200 nm) having the best balance of patterning potential, reproducibility and stability to be used in optical, sensing or electronic fields. The nanostructured HfO2 thin films with micropatterns or continuous morphologies were synthesized by two different methods, i.e., the micropatterning of sol-gel solutions by deep ultraviolet (DUV) photolithography or the electrophoretic deposition (EPD) of HfO2 nanoparticles (HfO2-NPs). Amorphous and monoclinic HfO2 micropatterned nanostructured thin films (HfO2-DUV) were prepared by using a sol-gel solution precursor (HfO2-SG) and spin-coating process following by DUV photolithography, whereas continuous and dense monoclinic HfO2 nanostructured thin films (HfO2-EPD) were prepared by the direct EPD of HfO2-NPs. The HfO2-NPs were prepared by a hydrothermal route and studied through the changing aging temperature, pH and reaction time parameters to produce nanocrystalline particles. Subsequently, based on the colloidal stability study, suspensions of the monoclinic HfO2-NPs with morphologies near spherical, spindle- and rice-like shapes were used to prepare HfO2-EPD thin films on conductive indium-tin oxide-coated glass substrates. Morphology, composition and crystallinity of the HfO2-NPs and thin films were investigated by powder and grazing incidence X-ray diffraction, scanning electron microscopy, transmission electron microscopy and UV-visible spectrophotometry. The EPD and DUV photolithography performances were explored and, in this study, it was clearly demonstrated that these two complementary methods are suitable, simple and effective processes to prepare controllable and tunable HfO2 nanostructures as with homogeneous, dense or micropatterned structures.

Nanostructured β-FeSi 2 and β-Fe 0.95 Co 0.05 Si 2 specimens with a relative density of up to 95% were synthesized by combining a top-down approach and spark plasma sintering. The thermoelectric properties of a 50 nm crystallite size β-FeSi 2 sample were compared to those of an annealed one, and for the former a strong decrease in lattice thermal conductivity and an upshift of the maximum Seebeck's coefficient were shown, resulting in an improvement of the figure of merit by a factor of 1.7 at 670 K. For β-Fe 0.95 Co 0.05 Si 2 , one observes that the figure of merit is increased by a factor of 1.2 at 723 K between long time annealed and nanostructured samples mainly due to an increase in the phonon scattering and an increase in the point defects. This results in both a decrease in the thermal conductivity to 3.95 W/mK at 330 K and an increase in the power factor to 0.63 mW/mK 2 at 723 K.

Polycrystalline higher manganese silicides Mn 1- x Cr x Si 1.74 ( x = 0, 0.10, 0.20) with Cr single doping and Mn 1-2 y Cr y Fe y Si 1.74 ( y = 0.10, 0.20) with Cr-Fe double doping have been prepared by arc melting and spark plasma sintering. Hall effect results and thermoelectric transport properties measurements demonstrate that Cr doping effectively increases the carrier concentration, thereby giving rise to enhanced electrical conductivity and power factor. Coupled with an enlarged effective mass and a reduction in the lattice thermal conductivity, a maximum zT is realized in Mn 0.90 Cr 0.10 Si 1.74 . It is also proved that the carrier concentration and carrier scattering mechanism could be altered through further doping on the Mn site by Fe, which leads to a lower electrical conductivity and higher Seebeck coefficient. Factors related to the suppression of the lattice thermal conductivity, like mass and strain field fluctuation scattering and electron-phonon scattering, are also analyzed. This work reveals the effects of Cr single doping and Cr-Fe dual-element doping on the carrier concentration, carrier scattering mechanism, and lattice thermal conductivity of higher manganese silicides.