Scalable Synthesis of Ultrathin Mn3N2 Exhibiting Room‐Temperature Antiferromagnetism

Ultrathin and 2D magnetic materials have attracted a great deal of attention recently due to their potential applications in spintronics. Only a handful of stable ultrathin magnetic materials have been reported, but their high‐yield synthesis remains a challenge. Transition metal (e.g., manganese) nitrides are attractive candidates for spintronics due to their predicted high magnetic transition temperatures. Here, a lattice matching synthesis of ultrathin Mn₃N₂ is employed. Taking advantage of the lattice match between a KCl salt template and Mn₃N₂, this method yields the first ultrathin magnetic metal nitride via a solution‐based route. Mn₃N₂ flakes show intrinsic magnetic behavior even at 300 K, enabling potential room‐temperature applications. This synthesis procedure offers an approach to the discovery of other ultrathin or 2D metal nitrides.     

Electrochromic Effect in Titanium Carbide MXene Thin Films Produced by Dip‐Coating

MXenes, a large family of 2D transition metal carbides and nitrides, have shown potential in energy storage and optoelectronic applications. Here, the optoelectronic and pseudocapacitive properties of titanium carbide (Ti₃C₂T_x) are combined to create a MXene electrochromic device, with a visible absorption peak shift from 770 to 670 nm and a 12% reversible change in transmittance with a switching rate of <1 s when cycled in an acidic electrolyte under applied potentials of less than 1 V. By probing the electrochromic effect in different electrolytes, it is shown that acidic electrolytes (H₃PO₄ and H₂SO₄) lead to larger absorption peak shifts and a higher change of transmittance than the neutral electrolyte (MgSO₄) (Δλ is 100 nm vs 35 nm and ΔT_{770 nm} is ≈12% vs ≈3%, respectively), hinting at the surface redox mechanism involved. Further investigation of the mechanism by in situ X‐ray diffraction and Raman spectroscopy reveals that the reversible shift of the absorption peak is attributed to protonation/deprotonation of oxide‐like surface functionalities. As a proof of concept, it is shown that Ti₃C₂T_x MXene, dip‐coated on a glass substrate, functions as both transparent conductive coating and active material in an electrochromic device, opening avenues for further research into optoelectronic and photonic applications of MXenes.     

Arbitrarily Shaped Fiber Assemblies from Spun Carbon Nanotube Gel Fibers

Experimental methods, apparatus, and practically useful theoretical analysis are provided for the coagulation‐based spinning of effectively unlimited lengths of carbon nanotube fibers having exceptional toughness and reasonably high strength. This spinning process fundamentally depends on the mechanical properties of intermediate gel state fibers, which we find are surprising elastic up to about 20 % strain and sufficiently strong for diverse processing methods. More specifically, we show that assemblies of these gel fibers can be used as intermediates for making nanotube sheets, large diameter fibers, and conformal coatings. When suitably processed, these composites (comprising many parallel solution‐spun nanotube fibers) have useful strength and extraordinary toughness.     

Fracture toughness anisotropy of partially stabilized ZrO2 crystals in the plane (001)

Partially stabilized ZrO₂ crystals doped with Tb₂O₃ exhibit fracture toughness anisotropy in the plane (001) in Vickers indentation. The anisotropy is determined over a range of loads that give rise to fully developed radial cracks around the indenter impression. Extensive lateral cracking and surface chipping obscure the observed anisotropy of fracture toughness at relatively high loads. Institute of Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 5, pp. 86–95, September–October, 1999.     

Bending single-walled carbon nanotubes into nanorings using a Pickering emulsion-based process

Single-walled carbon nanotube (SWCNT) nanorings have been fabricated on a large scale using a Pickering emulsion-based process. The formation mechanism was attributed to liquid/liquid interface-induced SWCNT bending. Mechanical analysis shows that curved water/1,2-dichlorobenzene interface created during the miniemulsion process is sufficient to bend the SWCNT into closed rings. Raman spectroscopy was used to study SWCNT structural change after the nanoring formation. It was shown that compressive and tensile strains were introduced in these rings. We anticipate that a variety of functionalized SWCNT nanorings can be fabricated using our method for various applications.     

Micro-raman studies on materials based on zirconium dioxide

Micro-Raman studies have been made on zirconium dioxide ceramics and crystals by the use of argon and helium-neon lasers. The Raman results for the crystals are appreciably affected by the wavelength, which is due to a luminescence spectrum more intense than the background (this is not usually characteristic of zirconium dioxide ceramics). When a crystal is indented, the monoclinic phase is detected only near the edges of the indent, so that process cannot be the cause of the rise in the surface around the indent. It is concluded that the crystals differ from the ceramics in that the monoclinic-tetragonal transition is not the mechanism that governs the mechanical behavior. Strength Problems Institute, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4(406), pp. 88–96, March–April, 1999.     

The role of microwave absorption on formation of graphene from graphite oxide

By means of manipulating the oxygen content in graphite oxides (GO) and/or graphene-based materials, we demonstrate that the microwave absorption capacity of carbon materials is highly dependent on their chemical composition and structure. The increase of oxygen in GO remarkably decreases its microwave absorption capacity due to the size decrease of the π–π conjugated structure in these materials, and vice versa. It was revealed that graphene is an excellent microwave absorbent while GO with poor microwave absorption capacity, the unoxidized graphitic region “impurities” in GO act as the microwave absorbents to initiate the microwave-induced deoxygenation. The addition of a small amount graphene to GO leads to avalanche-like deoxygenation reaction of GO under microwave irradiation (MWI) and graphene formation, which was used for electrode materials in supercapacitors. The interaction between microwaves and graphene or graphene-based materials may be used for the fabrication of a variety of graphene-based nanocomposites with exceptional properties and a wealth of practical applications.     

Local Fracture of Nanolaminates: Edge Chipping Test

Strength of Materials - The fracture resistance of domestic and foreign nanolaminate ceramics was studied by the EF (edge fracture) method. This method provides for indentor chipping of rectangular...     

An Ultrafast Conducting Polymer@MXene Positive Electrode with High Volumetric Capacitance for Advanced Asymmetric Supercapacitors

Pseudocapacitors or redox capacitors that synergize the merits of batteries and double‐layer capacitors are among the most promising candidates for high‐energy and high‐power energy storage applications. 2D transition metal carbides (MXenes), an emerging family of pseudocapacitive materials with ultrahigh rate capability and volumetric capacitance, have attracted much interest in recent years. However, MXenes have only been used as negative electrodes as they are easily oxidized at positive (anodic) potential. To construct a high‐performance MXene‐based asymmetric device, a positive electrode with a compatible performance is highly desired. Herein, an ultrafast polyaniline@MXene cathode prepared by casting a homogenous polyaniline layer onto a 3D porous Ti₃C₂T_x MXene is reported, which enables the stable operation of MXene at positive potentials because of the enlarged work function after compositing with polyaniline, according to the first‐principle calculations. The resulting flexible polyaniline@MXene positive electrode demonstrates a high volumetric capacitance of 1632 F cm^?3 and an ultrahigh rate capability with 827 F cm^?3 at 5000 mV s^?1, surpassing all reported positive electrodes. An asymmetric device is further fabricated with MXene as the anode and polyaniline@MXene as the cathode, which delivers a high energy density of 50.6 Wh L^?1 and an ultrahigh power density of 127 kW L^?1.