The chemistry of ternary and higher lithium nitrides

Synthesis of pyrimidines from dinitrogen and carbon

The element nitrogen and nitrogenous compounds are vital to life. The synthesis of nitrogen-containing compounds using dinitrogen as the nitrogen source, not through ammonia, is of great interest and great value but remains a grand challenge. Herein, we describe a strategy to realize this transformation by combining the heterogeneous approach with the homogeneous methodology. The N₂ molecule was first fixed with carbon and LiH through a one-pot heterogeneous process, forming Li₂CN₂ as an 'activated' nitrogen source with high efficiency. Then subsequent homogeneous treatments of Li₂CN₂ to construct the organic synthon carbodiimide and the RNA/DNA building block pyrimidines were fulfilled. By using ¹⁵N₂ as the feedstock, their corresponding ¹⁵N-labeled carbodiimide and pyrimidines were readily obtained. This homogeneous-heterogeneous synergy strategy will open a new chapter for N₂ transformation.

Highly efficient lithium adsorption and stable isotope separation by metal-organic frameworks

The effects of a series of MOFs on the adsorption and separation of lithium isotopes were investigated in this paper. Seven kinds of MOF were prepared, and the characterization studies of MIL-100(Fe) before and after adsorption by X-ray photoelectron spectroscopy (XPS) demonstrated the potential chemical interaction between Fe and Li. The influence of metal ions, counter-ions and solvents on the adsorption capacity and separation factor was investigated. The maximum separation factor can reach 1.048 ± 0.001. MIL-100(Fe) also has good regeneration performance.

Graphene oxide membranes with a confined mass transfer effect for Li+/Mg2+ separation: a molecular dynamics study

Molecular dynamics simulations were used to investigate the influence of the confined mass transfer effect on the separation of Mg2+ and Li+ from graphene oxide membranes, both in terms of layer spacing and degree of oxidation.

Novel Fluorine-Pillared Metal-Organic Framework for Highly Effective Lithium Enrichment from Brine

The continuously developing lithium battery market makes seeking a reliable lithium supply a top priority for technology companies. Although metal-organic frameworks have been extensively researched as adsorbents owing to their exceptional properties, lithium adsorption has been scarcely investigated. Herein, we prepared a novel cuboid rod-shaped three-dimensional framework termed TJU-21 composed of fluorine-pillared coordination layers of Fe-O inorganic chains and benzene-1,3,5-tricarboxylate (BTC) linkages. Besides thermal and chemical robustness, a remarkably high lithium uptake of about 41 mg·g^-1 was observed on TJU-21 as a fast-spontaneous endothermic process. Single-crystal X-ray diffraction demonstrated that the adsorbed lithium was located in the cavity symmetrically assembled by iron sites and organic ligands between adjacent layers, while another kind of cavity in the framework circled by Fe-O-Fe-O-Fe-O-Fe chains and shared BTC linkages was occupied by hydrogen-bonded water molecules. Lithium adsorption resulted in decreased curviness of the coordination layers, and the binding energy change at O 1s as well as the increased Fe 2p peak, suggested potential interaction with iron sites. The practicability of TJU-21 as a lithium adsorbent was further proved by the considerable capacity and selectivity in simulated salt brines with excellent reusability.

Low-dimensional magnetism in calcium nitridonickelate(II) Ca2NiN2

Calcium nitridonickelate(II) Ca₂NiN₂ has been prepared through a high-temperature and high-pressure azide-mediated redox reaction, demonstrating that this method can stabilise nitrides of late transition metals in relatively high oxidation states. Ca₂NiN₂ crystallizes in the Na₂HgO₂ structure type and displays low-dimensional antiferromagnetic ordering of Ni²⁺ spins.

Elastic, electronic, chemical bonding and thermodynamic properties of the ternary nitride Ca4TiN4: Ab initio predictions

In order to shed light on the unexplored properties of the ternary nitride Ca₄TiN₄, we report for the first time the results of an ab initio study of its structural, electronic, elastic, chemical bonding and thermodynamic properties. Calculated equilibrium structural parameters are in excellent concordance with available experimental data. Electronic properties were explored through the calculation of the energy band dispersions and density of states. It is found that Ca₄TiN₄ has an indirect band gap (Z-Γ) of 1.625 (1.701) eV using LDA (GGA). Nature of the chemical bonding was studied via Mulliken population analysis and charge density distribution map. It is found that the Ca-N bond is dominantly ionic, whereas the Ti-N one is dominantly covalent. Elastic properties of both single-crystal and polycrystalline phases of the title compound were explored in details using the stain-stress approach. Analysis of the calculated elastic moduli reveals that the title compound is mechanically stable, ductile and elastically anisotropic. Temperature and pressure dependencies of the unit-cell volume, bulk modulus, heat capacities, volume thermal expansion coefficient, Grüneisen parameter and Debye temperature were investigated based on the quasiharmonic Debye model.

Percolation behaviors of ionic and electronic transfers in Li3-2xCoxN

Nitridocobaltates Li3-2xCoxN, with Li3N-type layered structure, are promising compounds as negative electrode materials for Li-ion batteries. In the present paper, we report the first detailed broadband dielectric spectroscopy (BDS) study on lithiated transition metal nitrides. The ionic and electronic conductivities of Li3-2xCox□xN compounds (0 ≤ x ≤ 0.44) are investigated as a function of the concentration x of cobalt ions, cationic vacancies (□) and lithium ions. Dielectric and conductivity spectra were recorded within the frequency range of 60-1010 Hz from 200 to 300 K. Experimental results exhibit two types of electric conduction: the first one is due to lithium ion diffusion (for 0 ≤ x ≤ 0.25) and the second one due to electronic transfers (for x ≥ 0.3). Furthermore, two percolation transitions are evidenced and associated with 3D ionic transfers (threshold at x ≈ 0.11) on the one hand and 2D electronic transfers (threshold at x ≈ 0.30) on the other hand. Upon increasing the frequency, dielectric relaxations appear from larger to smaller sample scales. These successive polarizations appear with increasing frequency in the following order: (a) sample/silver paint interface; (b) particles (aggregates of grains); (c) grains (crystallites); (d) local ionic and electronic motions within the grains. Evolutions of dielectric relaxation parameters (dielectric strength and relaxation frequency) with Co content confirm the two percolation transitions. Surprisingly, the grain conductivity has a large discontinuity immediately below the electronic percolation threshold where any local- and long-range ionic movement disappears without electronic transfer. This discontinuity would be due to a narrow transition from ionic to electronic conduction when x increases.

Ammonothermal Synthesis of Nitrides: Recent Developments and Future Perspectives

Nitrides represent an intriguing class of functional materials with a broad range of application fields. Within the past decade, the ammonothermal method became increasingly attractive for the synthesis and crystal growth of nitride materials. The ammonothermal approach proved to be eminently suitable for the growth of bulk III-nitride semiconductors like GaN, and furthermore provided access to numerous ternary and multinary nitrides and oxonitrides with promising optical and electronic properties. In this minireview, we will shed light on the latest research findings covering the synthesis of nitrides by this method. An overview of synthesis strategies for binary, ternary, and multinary nitrides and oxonitrides, as well as their properties and potential applications will be given. The recent development of autoclave technologies for syntheses at high temperatures and pressures, in situ methods for investigations of crystallization processes, and solubility measurements by ultrasonic velocity experiments is briefly reviewed as well. In conclusion, challenges and future perspectives regarding the synthesis and crystal growth of novel nitrides, as well as the advancement of autoclave techniques are discussed.

Strategies Based on Nitride Materials Chemistry to Stabilize Li Metal Anode

Lithium metal battery is a promising candidate for high-energy-density energy storage. Unfortunately, the strongly reducing nature of lithium metal has been an outstanding challenge causing poor stability and low coulombic efficiency in lithium batteries. For decades, there are significant research efforts to stabilize lithium metal anode. However, such efforts are greatly impeded by the lack of knowledge about lithium-stable materials chemistry. So far, only a few materials are known to be stable against Li metal. To resolve this outstanding challenge, lithium-stable materials have been uncovered out of chemistry across the periodic table using first-principles calculations based on large materials database. It is found that most oxides, sulfides, and halides, commonly studied as protection materials, are reduced by lithium metal due to the reduction of metal cations. It is discovered that nitride anion chemistry exhibits unique stability against Li metal, which is either thermodynamically intrinsic or a result of stable passivation. The results here establish essential guidelines for selecting, designing, and discovering materials for lithium metal protection, and propose multiple novel strategies of using nitride materials and high nitrogen doping to form stable solid-electrolyte-interphase for lithium metal anode, paving the way for high-energy rechargeable lithium batteries.

Two-dimensional hydrogenated molybdenum and tungsten dinitrides MN2H2 (M = Mo, W) as novel quantum spin hall insulators with high stability

Based on first-principles calculations, we predict the existence of the quantum spin Hall (QSH) effect in hydrogenated transition-metal nitrides MN₂H₂ (M = Mo, W), showing high structural stability. MN₂H₂ monolayers are identified to be intrinsic topological insulators (TIs) with protected Dirac type topological helical edge states, and show robust topological features against the large stretching strain. Besides, sizeable intrinsic nontrivial band gaps (70-124 meV) ensure the QSH effect in MN₂H₂ at room temperature. The pure d-d band inversion was revealed. More interestingly, the topological phase transition between a QSH phase and a topological semimetallic phase can be induced by applying in-plane strain.

Li18 P6 N16 -A Lithium Nitridophosphate with Unprecedented Tricyclic [P6 N16 ]18- Ions

Li₁₈ P₆ N₁₆ was synthesized by reaction of LiPN₂ and Li₇ PN₄ at 5.5 GPa and 1273 K employing the multi-anvil technique. It is the first lithium nitridophosphate obtained by high-pressure synthesis. Moreover, it is the first example received by reaction of two ternary lithium nitrides. The combination of high-pressure conditions with a Li₃ N flux enabled a complete structure determination using single-crystal X-ray diffraction. The hitherto unknown tricyclic [P₆ N₁₆ ]^18- anion is composed of six vertex-sharing PN₄ tetrahedra forming one vierer- and two additional dreier-rings. To confirm the structure, Rietveld refinement, ⁷ Li and ³¹ P solid-state NMR spectroscopy, FTIR spectroscopy and EDX measurements were carried out. To validate the ionic properties, the migration pathways of the Li⁺ ions were evaluated, and the conductivity and its temperature dependence were determined by impedance spectroscopy measurements. In order to obtain a clearer picture of the formation mechanism of this compound class, different synthetic approaches were compared, enabling targeted syntheses of unprecedented P/N-anion topologies with intriguing properties.

Unravelling redox processes of Li7MnN4 upon electrochemical Li extraction–insertion using operando XAS

Evolution upon electrochemical oxidation of the Li₇MnN₄ Mn K-edge absorption spectra has been described using 3 distinctive local environments.

Low temperature synthesis of LiSi2N3 nanobelts via molten salt nitridation and their photoluminescence properties

LiSi₂N₃ nanobelts are synthesized using a novel low temperature MSN technique for the first time. The LiSi₂N₃ nanobelts show an optical band gap of 5.25 eV and exhibit an intense violet-blue PL emission with a peak at 459 nm at ambient temperature.

Pressure modulates the phase stability and physical properties of zinc nitride iodine

To explore new stable phases in metal nitride halides, the structural, electronic and optical properties, and chemical bonding characteristics of Zn₂NI under pressure were studied on the basis of crystal structure predicting evolution and density function calculations.

Electronic promoter or reacting species? The role of LiNH2 on Ru in catalyzing NH3 decomposition

Li creates a NH_x-rich environment and Ru mediates the electron transfer facilitating NH_x coupling.

Synthesis and luminescence properties of a novel red-emitting LiSr4(BN2)3:Eu2+phosphor

A near-UV excited phosphor, LiSr₄(BN₂)₃:Eu²⁺(LSBN:Eu²⁺), was synthesized using a solid-state reaction at 800 °C.

Theoretical study on the structural, electronic and physical properties of layered alkaline-earth-group-4 transition-metal nitrides AEMN2

Thermodynamic, structural, and electronic properties of the layered ternary nitrides AEMN₂ (AE = alkaline-earth; M = group 4 transition metal) both with the KCoO₂ and α-NaFeO₂ structure-types are examined within density-functional theory.