Liquid metal for high-entropy alloy nanoparticles synthesis.

High-entropy alloy nanoparticles (HEA-NPs) show great potential as functional materials1-3. However, thus far, the realized high-entropy alloys have been restricted to palettes of similar elements, which greatly hinders the material design, property optimization and mechanistic exploration for different applications4,5. Herein, we discovered that liquid metal endowing negative mixing enthalpy with other elements could provide a stable thermodynamic condition and act as a desirable dynamic mixing reservoir, thus realizing the synthesis of HEA-NPs with a diverse range of metal elements in mild reaction conditions. The involved elements have a wide range of atomic radii (1.24-1.97 Å) and melting points (303-3,683 K). We also realized the precisely fabricated structures of nanoparticles via mixing enthalpy tuning. Moreover, the real-time conversion process (that is, from liquid metal to crystalline HEA-NPs) is captured in situ, which confirmed a dynamic fission-fusion behaviour during the alloying process.

Connection between Unusual Lattice Thermal Expansion and Cooperative Jahn-Teller Effect in Double Perovskites LaPbMSbO6 (M = Mn, Co, Ni).

Lattice thermal expansion (LTE) has been investigated in double perovskites LaPbMSbO6 (M = Mn, Co, Ni). Ordinary LTE behavior with good thermal stability is identified for the Mn sample, whereas unusual LTE with a preferably expanded interplanar distance of (040) is revealed for Co and Ni samples. Temperature-dependent X-ray diffraction patterns ( T-XRD), Raman spectra ( T-Raman), and specific heat capacities ( T- Cp) consistently indicate that a rare isostructural displacive phase transition (IDPT) with a second-order phase transition nature is predominant near the critical temperature. Refinements of neutron powder diffraction (NPD) and in situ T-XRD data present temperature-sensitive bond parameters which are relevant to planar oxygen O1. X-ray photoelectron spectra (XPS) further confirm the Jahn-Teller (J-T) activated Co2+ (HS) or Ni3+ (HS/LS) cations at the B-site sublattice. This unusual LTE behavior could be understood by the cooperative J-T effect contributed by a Pb2+ ion and Co2+/Ni3+ ion from A- and B-site sublattices, respectively. The importance of 6s(Pb)-2p(O)-3d(Co/Ni) extended orbital hybridization on affecting thermal expansion behavior is highlighted on the basis of temperature-induced phonon mode softening. This study presents a microscopic description of connection between anisotropic thermal expansion and a cooperative J-T effect, which inspired exploration of thermal-mechanical coupled functional materials based on LaPbMSbO6 double perovskites.

First-principle investigation of magnetic coupling mechanism in hypothesized a-site-ordered perovskite YMn3Sc4O12.

We have systematically investigated the electronic and magnetic properties of hypothesized A-site-ordered perovskite YMn3Sc4O12 using first-principle calculation based on the density functional theory. Our calculated results predict that YMn3Sc4O12 is both thermodynamically and mechanically stable and its ground state is antiferromagnetic insulator. The Mn(3+) is in the high-spin state. More importantly, by comparison to YMn3Sc4O12, we point out that the empty Sc 3d orbital provides the Mn--O--Sc--O--Mn superexchange interaction, which is similar to its isostructural perovskite CaCu3Ti4O12, and enhances the antiferromagnetic interaction between Mn ions. From these calculations, we can clearly see that the empty 3d orbital plays an important role to realize superexchange interaction.

General Synthesis of MOF Nanotubes via Hydrogen-Bonded Organic Frameworks toward Efficient Hydrogen Evolution Electrocatalysts.

The application scope of metal-organic frameworks (MOFs) can be extended by rationally designing the architecture and components of MOFs, which can be achieved via a metal-containing solid templated strategy. However, this strategy suffers from low efficiency and provides only one specific MOF from one template. Herein, we present a versatile templated strategy in which organic ligands are weaved into hydrogen-bonded organic frameworks (HOFs) for the controllable and scalable synthesis of MOF nanotubes. HOF nanowires assembled from benzene-1,3,5-tricarboxylic acid and melamine via a simple sonochemical approach serve as both the template and precursor to produce MOF nanotubes with varied metal compositions. Hybrid nanotubes containing nanometal crystals and N-doped graphene prepared through a carbonization process show that the optimized NiRuIr alloy@NG nanotube exhibits excellent electrocatalytic HER activity and durability in alkaline media, outperforming most reported catalysts. The strategy proposed here demonstrates a pioneering study of combination of HOF and MOF, which shows great potential in the design of other nanosized MOFs with various architectures and compositions for potential applications.

Ultrathin high-κ antimony oxide single crystals.

Ultrathin oxides have been reported to possess excellent properties in electronic, magnetic, optical, and catalytic fields. However, the current and primary approaches toward the preparation of ultrathin oxides are only applicable to amorphous or polycrystalline oxide nanosheets or films. Here, we successfully synthesize high-quality ultrathin antimony oxide single crystals via a substrate-buffer-controlled chemical vapor deposition strategy. The as-obtained ultrathin antimony oxide single crystals exhibit high dielectric constant (~100) and large breakdown voltage (~5.7 GV m-1). Such a strategy can also be utilized to fabricate other ultrathin oxides, opening up an avenue in broadening the applicaitons of ultrathin oxides in many emerging fields.

Mn valence, magnetic, and electrical properties of LaMnO3+δ nanofibers by electrospinning.

LaMnO3+δ nanofibers have been prepared by electrospinning. The nearly 70% of Mn atoms is Mn4+, which is much higher than that in the nanoparticles. The average grain size of our fibers is approximately 20 nm, which is the critical size producing the nanoscale effect. The nanofibers exhibit a very broad magnetic transition with Tc≈255 K, and the Tc onset is around 310 K. The blocking temperature TB is 180 K. The sample shows weak ferromagnetic property above the TB and below Tc and superparamagnetic property near the Tc onset. The resistivity measurements show a metal-insulator transition near 210 K and an upturn at about 45 K.