Here, we report the synthesis of single-domain particles of chromium-substituted hexaferrites SrFe12-xCrxO19 (x = 0-8) via the citrate-nitrate auto-combustion method. The introduction of Cr3+ ions into the hexaferrite structure up to x = 5.5 led to a significant increase in the coercive force from 4.4 to 13.9 kOe and a rise in the natural ferromagnetic resonance frequency from 51 to 129 GHz, which was also accompanied by a gradual decrease in Curie temperature. According to anomalous XRD and Mössbauer spectroscopy, chromium ions predominantly enter the octahedral sites 2a, 12k, and 4f2. This correlates with reducing magnetization and magnetocrystalline anisotropy constant; however, the resulting anisotropy field increases and leads to the enhancement of the coercivity and FMR frequency. We also summarized the data obtained on Cr substitution and compared it with Al and Ga, which are also known to improve the hard magnetic properties of hexaferrites, and showed that the differences in their properties can be explained by the distribution features of the substituting ions in the hexaferrite lattice. Our findings demonstrate that chromium-substituted hexaferrites offer an effective route to enhance hard magnetic properties and high-frequency performance, paving the way for their integration into rare-earth-free permanent magnets, spintronic devices, and future generations of wireless technologies.

Solution-based synthesis of mixed ionic and electronic conductors (MIECs) has enabled the development of novel inorganic materials with implications for a wide range of energy storage applications. However, many technologically relevant MIECs contain toxic elements (Pb) or are prepared by using traditional high-temperature solid-state synthesis. Here, we provide a simple, low-temperature and size-tunable (50-90 nm) colloidal hot injection approach for the synthesis of NaSbS2 based MIECs using widely available and non-toxic precursors. Key synthetic parameters (cationic precursor, reaction temperature, and ligand) are examined to regulate the shape and size of the NaSbS2 nanocrystals (NCs). FTIR studies revealed that ligands with carboxylate functionality are coordinated to the surface of the synthesized NaSbS2 NCs. The synthesized NaSbS2 nanocrystals have electronic and ionic conductivities of 3.31 × 10-10 (e-) and 1.9 × 10-5 (Na+) S cm-1 respectively, which are competitive with the ionic and electrical conductivities of perovskite materials generated by solid-state reactions. This research gives a mechanistic understanding and post-synthetic evaluation of parameters influencing the formation of sodium antimony chalcogenides materials.

Double substitution of strontium hexaferrite by calcium and aluminum leads to a tremendous rise of hard magnetic properties, such as coercivity and natural ferromagnetic resonance frequency (NFMR). However, the properties are also inextricably linked to the material microstructure (especially, particle size), to the solid solution inhomogeneity as well as aluminum ions distribution among iron sites in crystal structure. In this work, we obtained M-type hexaferrite particles Sr(1-x/12)Ca(x/12)Fe(12-x)AlxO(19) (x = 4-6) via a facile citrate-nitrate auto-combustion method and studied the influence of the annealing temperature in a broad range on the microstructure, features of crystal structure and hard magnetic properties. At low annealing temperatures (900-1000 degrees C) hexaferrite nanoparticles with 90% of nominal Al content and a wide chemical distribution are formed. Next, with an increase in the annealing temperature the distribution significantly narrows, chemical composition becomes close to the nominal one and particles size transfer firstly to submicron, then to micron range. The aluminum distribution over iron sites is independent distinctly on the annealing temperature. For all the compositions single domain particles with the maximum coercivity values between 22.8 and 36 kOe are obtained at 1200 degrees C. At 900-1000 degrees C the samples demonstrate coercivities up to 25 kOe, while above 1300 degrees C, the crystallites begin to pass into a polydomain state with a reduced coercivity. The hexaferrites with narrow chemical distribution reveal resonance absorption in sub-terahertz band. The highest NFMR frequency of 270 GHz was observed for x = 5.5 sample annealed at 1400 degrees C.

Foam-like nanocomposites of the Ce-Fe-O system with two (c-CeO2, am-F2O3), three (c-CeO2, o-CeFeO3, a-F2O3), or four phases (c-CeO2, o-CeFeO3, a-F2O3, am-Fe2O3) were synthesized using the RedOx reaction of glycine-nitrate combustion. The glycine/nitrate ratio (G/N) varied from deficient (0.2, 0.4) and stoichiometric (0.6) to excess ratios of glycine (0.8, 1.0, 1.2, 1.4). PXRD, 57Fe Moeurossbauer spectroscopy, N2physisorption, TEM, H2-TPD, O2-TPD, and H2-TPR were used to examine the characteristics of the obtained samples. The average crystallite size of the obtained composites was in the range of 1.3-31.3 nm, 33.4-50.7 nm, and 10.1-33.9 nm for c-CeO2, o-CeFeO3, and a-Fe2O3, respectively. The lowest SBET (1.5 m2/g) belonged to the case of stoichiometric G/N, while the highest value (49.2 m2/g) was found in the case of the highest amount of glycine (G/N = 1.4); the latter case also had the largest total pore volume (Vp = 0.182 cm3/g) when compared to the others. Moreover, the advanced catalytic performance of foamy Ce-Fe-O-based nanocomposites toward H2 combustion in air was found with t10 = 275 & DEG;C, t50 = 345 & DEG;C, and Ea = 76.9 kJ/mol for sample G/N = 1.2. The higher activity of sample G/N = 1.2 in catalysis was attributed to different properties of the composite, including an appropriate component phase ratio, the smaller size of crystallites, higher specific surface area, higher reducibility,oxygen capacity, etc. The findings make it possible to carry out the directed synthesis of catalysts based on the Ce -Fe-O system with specific phases, dispersion, and morphological composition for efficient hydrogen oxidation at moderate temperatures.& COPY; 2023 Vietnam National University, Hanoi. Published by Elsevier B.V.This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Herein, we demonstrate the synthesis of sandwiched composite nanomagnets, which consist of hard magnetic Cr-substituted hexaferrite cores and magnetite outer layers. The hexaferrite plate-like nanoparticles, with average dimensions of 36.3 nm × 5.2 nm, were prepared via a glass crystallization method and were covered by spinel-type iron oxide via thermal decomposition of iron acetylacetonate in a hexadecane solution. The hexaferrite nanoplates act as seeds for the epitaxial growth of the magnetite, which results in uniform continuous outer layers on both sides. The thickness of the layers can be adjusted by controlling the concentration of metal ions. In this way, layers with an average thickness of 3.7 and 4.9 nm were obtained. Due to an atomically smooth interface, the magnetic composites demonstrate the exchange coupling effect, acting as single phases during remagnetization. The developed approach can be applied to any spinel-type material with matching lattice parameters and opens the way to expand the performance of hexaferrite nanomagnets due to a combination of various functional properties.

The wafer-scale synthesis of layered transitional metal dichalcogenides presenting good crystal quality and homogeneous coverage is a challenge for the development of next-generation electronic devices. This work explores a fairly unconventional growth method based on a two-step process consisting in sputter deposition of stochiometric MoS2 on Si/SiO2 substrates followed by nanosecond UV (248 nm) pulsed laser annealing. Large-scale 2H-MoS2 multi-layer films were successfully synthetized in a N2-rich atmosphere thanks to a fine-tuning of the laser annealing parameters by varying the number of laser pulses and their energy density. The identification of the optimal process led to the success in achieving a (002)-oriented nanocrystalline MoS2 film without performing post-sulfurization. It is noteworthy that the spatial and temporal confinement of laser annealing keeps the Si/SiO2 substrate temperature well below the back-end-of-line temperature limit of Si CMOS technology (770 K). The synthesis method described here can speed up the integration of large-area 2D materials with Si-based devices, paving the way for many important applications.

In this study, we demonstrate the sintering of metastable ε-Fe2O3 nanoparticles into nanoceramics containing 98 wt% of the epsilon iron oxide phase and with a specific density of 60%. At room temperature, the ceramics retain a giant coercivity of 20 kOe and a sub-terahertz absorption at 190 GHz inherent in the initial nanoparticles. The sintering leads to an increase in the frequencies of the natural ferromagnetic resonance at 200-300 K and larger coercivities at temperatures below 150 K. We propose a simple but working explanation of the low-temperature dynamics of the macroscopic magnetic parameters of the ε-Fe2O3 materials via the transition of the smallest nanoparticles into a superparamagnetic state. The results are confirmed by the temperature dependence of the magnetocrystalline anisotropy constant and micromagnetic modeling. In addition, based on the Landau-Lifshitz formalism, we discuss features of the spin dynamics in ε-Fe2O3 and the possibility of using nanoceramics as sub-terahertz spin-pumping media. Our observations will expand the applicability of ε-Fe2O3 materials and promote their integration into telecommunication devices of the next generation.

The colloidal nanoparticles produced from bulk metal by laser ablation in water usually oxidize during aging. Such transformation could be used as a tool for nanoarchitecture if the control parameters are known. Here we studied in detail the transformation of copper-based nanoparticles in water during the colloid aging and the evolution of nanoparticle morphology at various temperatures. The spherical Cu@Cu2O core-shell nanoparticles were produced by laser ablation of Cu target in water. The aging of prepared colloid was investigated in situ by UV-visible absorption spectroscopy. The nanoparticle morphology and composition were characterized by scanning and transmitting electron microscopies, X-ray photoelectron and Raman spectroscopies. The aging of colloidal nanoparticles resulted in morphology changes and composition transformation to CuO. The nano particle sizes enlarged due to Ostwald ripening and aggregative growth either isotropically at room temperature (25 & DEG;C) or by forming elongated nano-spindles at temperature above 35 & DEG;C. The occurred transformation was characterized by Kolmogorov-Johnson-Mehl-Avrami approach which allowed to extract the activation energy of the process. The obtained results are useful for both nanoarchitecture and gaining colloid stability.

Direct colloidal synthesis of multinary metal chalcogenide nanocrystals typically develops dynamically from the binary metal chalcogenide nanocrystals with the subsequent incorporation of additional metal cations from solution during the growth process. Metal seeding of binary and multinary chalcogenides is also established, although the seed is solely a catalyst for nanocrystal nucleation and the metal from the seed has never been exploited as active alloying nuclei. Here we form colloidal Cu-Bi-Zn-S nanorods (NRs) from Bi-seeded Cu2-xS heterostructures. The evolution of these homogeneously alloyed NRs is driven by the dissolution of the Bi-rich seed and recrystallization of the Cu-rich stem into a transitional segment, followed by the incorporation of Zn2+ to form the quaternary Cu-Bi-Zn-S composition. The present study also reveals that the variation of Zn concentration in the NRs modulates the aspect ratio and affects the nature of the majority charge carriers. The NRs exhibit promising thermoelectric properties with very low thermal conductivity values of 0.45 and 0.65 W/mK at 775 and 605 K, respectively, for Zn-poor and Zn-rich NRs. This study highlights the potential of metal seed alloying as a direct growth route to achieving homogeneously alloyed NRs compositions that are not possible by conventional direct methods or by postsynthetic transformations.

In this paper, we have developed a 'phosphine-free' method for synthesising copper telluride nanocrystals using diphenyl ditelluride as an air-stable tellurium source. The diphenyl ditelluride is shown to have optimal reactivity for the colloidal synthesis of Cu2Te, allowing optimal control over the phase and morphology. Using this unexplored Te precursor for copper telluride synthesis, 1D nanorods of hexagonal phase (Cu2Te) were synthesised at a moderate temperature of 180 °C. The precise control over key parameters for this system results in Cu2-xTe nanocrystals forming with varied shapes (1D nanorods and 2D nanoplates), sizes, and crystal phases (hexagonal Cu2Te and orthorhombic Cu1.43Te).

Herein, we demonstrate the synthesis of sandwiched composite nanomagnets, which consist of hard magnetic hexaferrite cores and magnetite outer layers. The hexaferrite plate-like nanoparticles with average dimensions of 16.0 nm × 4.9 nm were prepared by glass crystallization method and were covered by spinel-type iron oxide via thermal decomposition of iron acetylacetonate in hexadecane solution. The hexaferrite nanoplates act as seeds for the epitaxial growth of the magnetite, which results in uniform continuous outer layers on both sides. The thickness of the layers can be adjusted by controlling the concentration of metal ions. In this way, layers with average thickness of 3.9 and 5.0 nm were obtained. Due to an atomically smooth interface the magnetic composites demonstrate the exchange coupling effect acting as single phases during remagnetization. The developed approach can be applied to any spinel-type material with matching lattice parameters and opens the way to expanding the performance of hexaferrite nanomagnets due to a combination of various functional properties.

Herein, we demonstrate for the first time compact ferrite ceramics with giant coercivity. The materials are manufactured via sintering single-domain Sr0.67Ca0.33Fe8Al4O19 particles synthesized by a citrate-nitrate auto-combustion method. The obtained ceramics show coercivities up to 22.5 kOe and natural ferromagnetic resonance frequencies (NFMR) in a sub-THz range of 160-282 GHz. At a maximum density of 95%, the sample displays coercivity of 18.5 kOe, which is the highest value among dense ferrite materials reported so far. In addition, we report an unusual blueshift of the NFMR frequency from 160 to 200 GHz, which occurs during material sintering.

The solution-based colloidal synthesis of multinary semiconductor compositions has allowed the design of new inorganic materials impacting a large variety of applications. Yet there are certain compositions that have remained elusive-particularly quaternary structures of transition metal-based (e.g., Co, Zn, Ni, Fe, Mn, and Cr) copper antimony chalcogenides. These are widely sought for tuning the electrical and thermal conductivity as a function of the size, composition, and crystal phase. In this work, a facile hot injection approach for the synthesis of three different tetrahedrite-substituted nanocrystals (NCs) (Cu10Zn2Sb4S13, Cu10Co2Sb4S13, and Cu10Ni1.5Sb4S13) and their growth mechanisms are investigated. We reveal that the interplay between the Zn, Ni, and Co precursors on the basis of thiophilicity is key to obtaining pure phase NCs with controlled size and shape. While all of the synthesized crystal phases display outstanding low thermal conductivity, the Cu10.5Sb4Ni1.5S13 system shows the most enhanced electrical conductivity compared to Cu10Zn2Sb4S13 and Cu10Co2Sb4S13. This study highlights an effective synthesis strategy for the growth of complex quaternary nanocrystals and their high potential for application in thermoelectrics.

Fine particles of SrFe12−xGaxO19 (x = 0–6) were obtained via a citrate auto-combustion route. Their magnetic and microwave absorption properties, as well as the features of the crystal structure were studied in detail.

Graphical Abstract Hydrogen reduction of Ni-doped phyllosilicate nanoscrolls yielded a Ni/silicate composite with tubular morphology. Formation of sepiolite-like phase during chrysotile dehydroxylation served as a sterical hindrance for complete Ni reduction. The resulting composite can be used in a variety of catalytical processes. Here, its performance in hydrogenation reactions was studied. More information can be found in the Full Paper by Andrei A. Krasilin et al.

Here we report the formation of three distinct Sn-based active materials for Li-ion battery anodes, formed from the same metal-organic material (MOM) precursor sql-1-Cu-SNIFSIX. The materials were obtained under three different anneal conditions in air, Ar, and a Se-rich atmosphere, leading to the selective formation of SnO2/CuO/C (oxide), Cu6Sn5/C (stannide), and Cu2SnSe3/SnSe2/C (selenide) composites. The lithiation and delithiation mechanisms were investigated for each material in the potential range of 0-3 V. Over extended cycling periods, the reversible alloying of Li with Sn was the only process evident for the stannide, with minimal activity occurring at potentials greater than 1 V. In contrast to this, the oxide and selenide composites exhibit both conversion (1-3 V) and Li/Sn alloying (0-1 V) behavior in this potential range; however, the stability of the conversion reaction was found to be poor, inhibiting the capacity retention of both materials. Notably, when the reaction mechanisms were restricted to Li/Sn alloying only by limiting the potential range to 0-1 V, all three composite materials significantly outperformed a Sn nanopowder electrode, illustrating the benefits of utilizing composite electrodes to stabilize the Sn alloying reaction over extended cycling periods.

This conference contribution is focused on decoration of WS2 nanotubes (NT-WS2) with gold and silver nanoparticles via facile routes implying direct reaction of tungsten disulfide with water-soluble AuIII and AgI species at 100°C. The underlying mechanism of these interactions will be discussed in details based on extensive studies of reaction mixtures and resulting metal–NT-WS2 nanocomposites, including thorough X-ray photoelectron spectroscopy (XPS) analysis. Surprising features in optical spectra of the designed nanocomposites would be reported, including suppression of plasmon resonance in tiny noble metal nanoparticles (< 10 nm in diameter) grown onto NT-WS2. The plasmonic features of individual gold nanoparticles on the surface of disulfide nanotube were also characterized by electron energy loss spectroscopy in scanning transmission electron microscopy mode (STEM-EELS). Photoresistive NO2−sensing response of NT-WS2 under green light illumination (λmax = 530 nm) and its enhancement by plasmonic gold “nanoantennas” will be reported as well.

The incorporation of Ge into SixGe1−x alloy NWs with their amorphization boosted their performance in Na-ion batteries as compared to parent a-Si and a-Ge NWs.