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Two-dimensional carbides and nitrides of transition metals, known as MXenes, are a fast-growing family of materials that have attracted attention as energy storage materials. MXenes are mainly prepared from Al-containing MAX phases (where A = Al) by Al dissolution in F-containing solution; most other MAX phases have not been explored. Here a redox-controlled A-site etching of MAX phases in Lewis acidic melts is proposed and validated by the synthesis of various MXenes from unconventional MAX-phase precursors with A elements Si, Zn and Ga. A negative electrode of Ti 3 C 2 MXene material obtained through this molten salt synthesis method delivers a Li + storage capacity of up to 738 C g −1 (205 mAh g −1 ) with high charge–discharge rate and a pseudocapacitive-like electrochemical signature in 1 M LiPF 6 carbonate-based electrolyte. MXenes prepared via this molten salt synthesis route may prove suitable for use as high-rate negative-electrode materials for electrochemical energy storage applications. Two-dimensional transition metal carbides and nitrides, known as MXenes, are currently considered as energy storage materials. A generic Lewis acidic etching route for preparing high-rate negative-electrode MXenes with enhanced electrochemical performance in non-aqueous electrolyte is now proposed.

The large class of layered ceramics encompasses both van der Waals (vdW) and non-vdW solids. While intercalation of noble metals in vdW solids is known, formation of compounds by incorporation of noble-metal layers in non-vdW layered solids is largely unexplored. Here, we show formation of Ti 3 AuC 2 and Ti 3 Au 2 C 2 phases with up to 31% lattice swelling by a substitutional solid-state reaction of Au into Ti 3 SiC 2 single-crystal thin films with simultaneous out-diffusion of Si. Ti 3 IrC 2 is subsequently produced by a substitution reaction of Ir for Au in Ti 3 Au 2 C 2 . These phases form Ohmic electrical contacts to SiC and remain stable after 1,000 h of ageing at 600 °C in air. The present results, by combined analytical electron microscopy and ab initio calculations, open avenues for processing of noble-metal-containing layered ceramics that have not been synthesized from elemental sources, along with tunable properties such as stable electrical contacts for high-temperature power electronics or gas sensors. Substitution of Si with Au and Ir in Ti 3 SiC 2 through a solid-state diffusion process allows the synthesis of Ti 3 AuC 2 , Ti 3 Au 2 C 2 and Ti 3 IrC 2 phases able to form Ohmic contacts with SiC stable at high temperatures under ambient air conditions.

Gold-associated pathfinder minerals have been investigated by identifying host minerals of Au for samples collected from an artisanal mining site near a potential gold mine (Kubi Gold Project) in Dunkwa-On-Offin in the central region of Ghana. We find that for each composition of Au powder (impure) and the residual black hematite/magnetite sand that remains after gold panning, there is a unique set of associated diverse indicator minerals. These indicator minerals are identified as SiO 2 (quartz), Fe 3 O 4 (magnetite) and Fe 2 O 3 (hematite), while contributions from pyrite, arsenopyrites, iridosmine, scheelite, tetradymite, garnet, gypsum and other sulfate materials are insignificant. This constitutes a confirmative identification of Au pathfinding minerals in this particular mineralogical area. The findings suggest that X-ray diffraction could also be applied in other mineralogical sites to aid in identifying indicator minerals of Au and the location of ore bodies at reduced environmental and exploration costs.

Reduced graphene oxide (rGO)/Bi2Te3 nanocomposite powders with different contents of rGO have been synthesized by a one-step in-situ reductive method. Then, rGO/Bi2Te3 nanocomposite bulk materials were fabricated by a hot-pressing process. The effect of rGO contents on the composition, microstructure, TE properties, and carrier transportation of the nanocomposite bulk materials has been investigated. All the composite bulk materials show negative Seebeck coefficient, indicating n-type conduction. The electrical conductivity for all the rGO/Bi2Te3 nanocomposite bulk materials decreased with increasing measurement temperature from 25 °C to 300 °C, while the absolute value of Seebeck coefficient first increased and then decreased. As a result, the power factor of the bulk materials first increased and then decreased, and a power factor of 1340 μWm−1K−2 was achieved for the nanocomposite bulk materials with 0.25 wt% rGO at 150 °C.

HighlightsSmall size V2SnC MAX phase was prepared by the molten salt method.V2SnC MAX phase electrode is able to deliver high gravimetric capacity up to 490 mAh g−1 and volumetric capacity of 570 mAh cm−3A charge storage mechanism with V2C-Li redox and Sn–Li alloying dual reactions was proposedMAX phases are gaining attention as precursors of two-dimensional MXenes that are intensively pursued in applications for electrochemical energy storage. Here, we report the preparation of V2SnC MAX phase by the molten salt method. V2SnC is investigated as a lithium storage anode, showing a high gravimetric capacity of 490 mAh g−1 and volumetric capacity of 570 mAh cm−3 as well as superior rate performance of 95 mAh g−1 (110 mAh cm−3) at 50 C, surpassing the ever-reported performance of MAX phase anodes. Supported by operando X-ray diffraction and density functional theory, a charge storage mechanism with dual redox reaction is proposed with a Sn–Li (de)alloying reaction that occurs at the edge sites of V2SnC particles where Sn atoms are exposed to the electrolyte followed by a redox reaction that occurs at V2C layers with Li. This study offers promise of using MAX phases with M-site and A-site elements that are redox active as high-rate lithium storage materials.

AlMgB 14 coatings have been deposited by DC magnetron sputtering from elemental targets on Si (001), Al 2 O 3 (0001) and MgO (001) substrates at temperatures in the range of 25–350 °C. The structural and mechanical properties of AlMgB 14 films were characterized by X-ray diffraction, scanning electron microscopy, nanoindentation, and analyzed as a function of deposition conditions and substrate materials. The results show that all films are X-ray amorphous, and the mechanical properties of the deposited films depend on the substrate and growth temperature. AlMgB 14 thin films deposited at 350 °C are found to have smoother surfaces and containing more well-formed B 12 icosahedra than the films deposited at lower temperature, which consequently increase the hardness of the deposited films. The maximum hardness and Young’s modulus of the as-deposited films are about 32.3 GPa and 310 GPa, respectively, for films deposited on Al 2 O 3 substrate at 350 °C.

Solid‐state precipitation can be used to tailor material properties, ranging from ferromagnets and catalysts to mechanical strengthening and energy storage. Thermoelectric properties can be modified by precipitation to enhance phonon scattering while retaining charge‐carrier transmission. Here, unconventional Janus‐type nanoprecipitates are uncovered in Mg3Sb1.5Bi0.5 formed by side‐by‐side Bi‐ and Ge‐rich appendages, in contrast to separate nanoprecipitate formation. These Janus nanoprecipitates result from local comelting of Bi and Ge during sintering, enabling an amorphous‐like lattice thermal conductivity. A precipitate size effect on phonon scattering is observed due to the balance between alloy‐disorder and nanoprecipitate scattering. The thermoelectric figure‐of‐merit ZT reaches 0.6 near room temperature and 1.6 at 773 K. The Janus nanoprecipitation can be introduced into other materials and may act as a general property‐tailoring mechanism. Bi‐/Ge‐rich Janus nanoprecipitates in Mg3Sb1.5Bi0.5 compounds are uncovered by electron microscopy and atom probe tomography. This complex Janus nanoprecipitate results from local comelting of Bi and Ge during sintering and enables an amorphous‐like lattice thermal conductivity near room temperature. The mechanistic understanding of thermal‐conductivity reduction is supported by modelling the material systems with and without precipitates.

A two-step synthesis approach was utilized to grow CaMnO3 on M-, R- and C-plane sapphire substrates. Radio-frequency reactive magnetron sputtering was used to grow rock-salt-structured (Ca, Mn)O followed by a 3-h annealing step at 800 °C in oxygen flow to form the distorted perovskite phase CaMnO3. The effect of temperature in the post-annealing step was investigated using x-ray diffraction. The phase transformation to CaMnO3 started at 450 °C and was completed at 550 °C. Films grown on R- and C-plane sapphire showed similar structure with a mixed orientation, whereas the film grown on M-plane sapphire was epitaxially grown with an out-of-plane orientation in the [202] direction. The thermoelectric characterization showed that the film grown on M-plane sapphire has about 3.5 times lower resistivity compared to the other films with a resistivity of 0.077 Ωcm at 500 °C. The difference in resistivity is a result from difference in crystal structure, single orientation for M-plane sapphire compared to mixed for R- and C-plane sapphire. The highest absolute Seebeck coefficient value is − 350 µV K−1 for all films and is decreasing with temperature.

Transition metal nitrides are a fascinating class of hard coating material that provides an excellent platform for investigating superconductivity and fundamental electron‐phonon (e‐ph) interactions. In this work, the structural, morphological, and superconducting properties have been studied for Mo2N thin films deposited via direct current magnetron sputtering on c‐plane Al2O3 and MgO substrates to elucidate the effect of internal strain on superconducting properties. High‐resolution X‐ray diffraction and time‐of‐flight elastic recoil detection analysis confirm the growth of single‐phase Mo2N thin films exhibiting epitaxial growth with twin‐domain structure. Low‐temperature electrical transport measurements reveal superconducting transitions at ≈5.2 and ≈5.6 K with corresponding upper critical fields of ≈5 and ≈7 T for the films deposited on Al2O3 and MgO, respectively. These results indicate strong type‐II superconductivity, and the observed differences in superconducting properties are attributed to substrate‐induced strain, which leads to higher e‐ph coupling for the film on MgO substrate. These findings highlight the tunability of superconducting properties in Mo2N films through strategic substrate selection. Compressive strain in Mo2N thin films on MgO substrates significantly enhances electron‐phonon coupling, resulting in a ∼25% increase in the upper critical field compared to films on Al2O3 substrate. This finding demonstrates an effective strategy for achieving higher‐performance superconducting devices by utilizing strain as a tunable parameter to optimize superconducting properties.

Flexible thermoelectric generators (f-TEGs) are of importance for self-powered, portable, and wearable electronics. The materials’ thermoelectric (TE) performance is one of the factors that affect the conversion efficiency of f-TEGs. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a kind of conducting polymers has low thermal conductivity and good processability in solution; however, its TE properties are still much lower than those of the inorganic TE materials, which limits its wide applications in f-TEGs. Two-dimensional (2D) inorganic nanosheets (NSs) exfoliated from their corresponding powders are promising filler materials for enhancing the TE properties of PEDOT:PSS. This paper provides a brief review on the research progress of flexible 2D inorganic NS/PEDOT:PSS composite films fabricated by vacuum filtration, drop casting, and spin coating. The challenges, perspectives, and outlooks of flexible 2D inorganic NS/PEDOT:PSS composite films are further discussed.