Influence of electronic correlation on the valley and topological properties of VSiGeP4 monolayer.

Valley is used as a new degree of freedom for information encoding and storage. In this work, the valley and topological properties of the VSiGeP4 monolayer were studied by adjusting the U value based on first-principles calculations. The VSiGeP4 monolayer remains in a ferromagnetic ground state regardless of the change in the U value. The magnetic anisotropy of the VSiGeP4 monolayer is initially in-plane, and then turns out-of-plane with the increase in the U value. Moreover, a topological phase transition is observed in the present VSiGeP4 monolayer with the increase in U value from 0 to 3 eV, i.e., the VSiGeP4 monolayer behaves as a bipolar magnetic semiconductor, a ferrovalley semiconductor, a half-valley metal characteristic, and a quantum anomalous Hall state. The mechanism of the topological phase transition behavior of the VSiGeP4 monolayer was analyzed. It was found that the variation in U values would change the strength of the electronic correlation effect, resulting in the valley and topological properties. In addition, carrier doping was studied to design a valleytronic device using this VSiGeP4 monolayer. By doping 0.05 electrons per f.u., the VSiGeP4 monolayer with a U value of 3 eV exhibits 100% spin polarization. This study indicates that the VSiGeP4 monolayer has potential applications in spintronic, valleytronic, and topological electronic nanodevices.

In Situ Preparation of Three-Dimensional Porous Nickel Sulfide as a Battery-Type Supercapacitor.

A one-step sulfurization method to fabricate Ni3S2 nanowires (Ni3S2 NWs) directly on a Ni foam (NF) was developed as a simple, low-cost synthesis method for use as a supercapacitor (SC), aimed at optimizing energy storage. Ni3S2 NWs have high specific capacity and are considered a promising electrode material for SCs; however, their poor electrical conductivity and low chemical stability limit their applications. In this study, highly hierarchical three-dimensional porous Ni3S2 NWs were grown directly on NF by a hydrothermal method. The feasibility of the use of Ni3S2/NF as a binder-free electrode for achieving high-performance SCs was examined. Ni3S2/NF exhibited a high specific capacity (255.3 mAh g-1 at a current density of 3 A g-1), good rate capability (2.9 times higher than that of the NiO/NF electrode), and competitive cycling performance (capacity retention of specific capacity of 72.17% after 5000 cycles at current density of 20 A g-1). Owing to its simple synthesis process and excellent performance as an electrode material for SCs, the developed multipurpose Ni3S2 NWs electrode is expected to be a promising electrode for SC applications. Furthermore, the synthesis method of self-growing Ni3S2 NW electrodes on 3D NF via hydrothermal reactions could potentially be applied to the fabrication of SC electrodes using a variety of other transition metal compounds.

Revealing the substitution preference of zinc in ordinary Portland cement clinker phases: A study from experiments and DFT calculations.

Ordinary Portland cement (OPC) clinker mainly consist four minerals, tricalcium silicate (C3S), dicalcium silicate (C2S,), tricalcium aluminate (C3A), and tetracalcium aluminoferrite (C4AF). To learn the doping behaviors of Zn in OPC clinker, a series of samples were prepared by calcinating the mixtures of CaCO3, SiO2, Al2O3, Fe2O3, and ZnO. Our results from energy-dispersive spectroscopy, X-ray diffraction and density functional theoretical simulations show that a small amount of ZnO enter C3S and C2S by replacing Ca ions while most incorporate into C4AF by substituting Fe atoms, resulting in a decrease of C3A in OPC as dosage increases. Further analyses from partial density of states and distributions of bond order-bond length indicate that the doping preference can be ascribed to the similar electron contributions and small structure distortions between host and guest ions. Unlike the strong Fe‒O bond, the newly formed Zn‒O is much weaker. The weak Zn‒O may be responsible for the limited solubility of Zn in C4AF. These results provide a possibility of increasing solubility of Zn in OPC clinker by increasing the contents of C3A and C4AF, thus will be very meaningful in the synthesis of OPC clinker by utilizing Zn-bearing alternative raw materials.

Flexible, Water-Resistant and Air-Stable LiBH4 Nanoparticles Loaded Melamine Foam With Improved Dehydrogenation.

Flexible, water-resistant, and air-stable hydrogen storage material (named PMMA-LiBH4/GMF), consisting of LiBH4 nanoparticles confined by poly (methylmethacrylate) (PMMA) and reduced graphene oxide (rGO) modified melamine foam (GMF), were prepared by a facile method. PMMA-LiBH4/GMF can recover original shape after compression at the strain of 50% and exhibits highly hydrophobic property (water contact angle of 123°). Owing to the highly hydrophobic property and protection of PMMA, PMMA-LiBH4/GMF demonstrates outstanding water-resistance and air-stability. Significantly, the onset dehydrogenation temperature of PMMA-LiBH4/GMF at first step is reduced to 94°C, which is 149°C less than that of LiBH4/GMF, and the PMMA-LiBH4/GMF desorbs 2.9 wt% hydrogen within 25 min at 250°C, which is obviously more than the dehydrogenation amount of LiBH4/GMF under the same conditions. It's our belief that the flexible, water-resistant and air-stable PMMA-LiBH4/GMF with a simple preparation route will provide a new avenue to the research of hydrogen storage materials.