Synthesis, structure, electric, and magnetic properties of CaNiN

Spin Chains with Highly Quantum Character through Strong Covalency in Ca3CrN3

The insulating transition metal nitride Ca3CrN3 consists of sheets of triangular [CrN3]6- units with C2v symmetry that are connected via quasi-1D zigzag chains. Due to strong covalency between Cr and N, Cr3+ ions are unusually low-spin, and S = 1/2. Magnetic susceptibility measurements reveal dominant quasi-1D spin correlations with very large nearest-neighbor antiferromagnetic exchange J = 340 K and yet no sign of magnetic order down to T = 0.1 K. Density functional theory calculations are used to model the local electronic structure and the magnetic interactions, supporting the low-spin assignment of Cr3+ that is driven by strong π donation from the nitride ligands. The surprising failure of interchain exchange to drive long-range magnetic order is accounted for by the complex connectivity of the spin chain pairs that further frustrates order. Our combined results establish Ca3CrN3 as a nearly ideal manifestation of a quantum spin chain whose dynamics remain unquenched down to extraordinarily low temperatures despite strong near-neighbor exchange coupling.

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.

Coloring and distortion variants of the bcc packing and for the aristotypes BaAl4 and CeMg2Si2

The huge number of intermetallic structure types with many representatives calls for structural systemization. The combination of crystal chemistry with group theory is an efficient tool for such systemization and can be displayed in a concise and compact way via group-subgroup schemes. The present overview deals with such group-subgroup schemes (Bärnighausen trees) for coloring and distortion variants of the bcc packing as well as superstructures that derive from the aristotypes BaAl4 and CeMg2Si2.

Achievements, Challenges, and Prospects of Calcium Batteries

This Review flows from past attempts to develop a (rechargeable) battery technology based on Ca via crucial breakthroughs to arrive at a comprehensive discussion of the current challenges at hand. The realization of a rechargeable Ca battery technology primarily requires identification and development of suitable electrodes and electrolytes, which is why we here cover the progress starting from the fundamental electrode/electrolyte requirements, concepts, materials, and compositions employed and finally a critical analysis of the state-of-the-art, allowing us to conclude with the particular roadblocks still existing. As for crucial breakthroughs, reversible plating and stripping of calcium at the metal-anode interface was achieved only recently and for very specific electrolyte formulations. Therefore, while much of the current research aims at finding suitable cathodes to achieve proof-of-concept for a full Ca battery, the spectrum of electrolytes researched is also expanded. Compatibility of cell components is essential, and to ensure this, proper characterization is needed, which requires design of a multitude of reliable experimental setups and sometimes methodology development beyond that of other next generation battery technologies. Finally, we conclude with recommendations for future strategies to make best use of the current advances in materials science combined with computational design, electrochemistry, and battery engineering, all to propel the Ca battery technology to reality and ultimately reach its full potential for energy storage.

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.

A color tunable and white light emitting Ca2Si5N8:Ce3+,Eu2+ phosphor via efficient energy transfer for near-UV white LEDs

Achieving tunable color and white light emission in a single phase phosphor is a challenging issue. Here, a series of Ce3+-Eu2+ co-doped Ca2Si5N8 phosphors were successfully synthesized by a high temperature solid state method. Luminescence properties, energy transfer (ET) and thermal quenching of the as-synthesized samples were investigated in detail. The emission color of as-prepared Ca1.94Na0.03Si5N8:0.03Ce3+,yEu2+ (0.0000 ≤ y ≤ 0.0035) could be tuned from blue to white light and eventually to orange via ET by changing the Ce3+/Eu2+ ratio. ET efficiency from Ce3+ to Eu2+ could reach up to 68.0% and the ET mechanism was demonstrated to be a non-radiative dipole-dipole interaction. More importantly, when y = 0.0012, approximate standard white light was generated with CIE coordinates of (0.335, 0.341). A photoluminescence (PL) mechanism was proposed to understand PL properties and thermal properties of the as-prepared phosphors. Additionally, the achieved white light phosphor Ca1.9388Na0.03Si5N8:0.03Ce3+,0.0012Eu2+ had good thermal stability, exhibiting about 75% at 150 °C and 64% at 200 °C of the emission intensity at 25 °C, respectively. The chromaticity shifts of Ca1.9388Na0.03Si5N8:0.03Ce3+,0.0012Eu2+ were 0.0032 at 150 °C and 0.0152 at 200 °C, respectively, which were only 27% and 42% of the commercial white-emitting phosphor mixture at the corresponding temperature. Furthermore, a proof-of-concept white LED was fabricated by combining the single component phosphor Ca1.9388Na0.03Si5N8:0.03Ce3+,0.0012Eu2+ with a near UV LED chip. All results demonstrate the promising application of the Ca2Si5N8:Ce3+,Eu2+ single phosphor for near-UV white LEDs.

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.

Crystal chemistry and electronic structure of the metallic lithium ion conductor, LiNiN

The layered ternary nitride LiNiN shows an interesting combination of fast Li+ ion diffusion and metallic behavior, properties which suggest potential applications as an electrode material in lithium ion batteries. A detailed investigation of the structure and properties of LiNiN using powder neutron diffraction, ab initio calculations, SQUID magnetometry, and solid-state NMR is described. Variable-temperature neutron diffraction demonstrates that LiNiN forms a variant of the parent Li3N structure in which Li+ ion vacancies are ordered within the [LiN] planes and with Ni exclusively occupying interlayer positions (at 280 K: hexagonal space group Pm2, a = 3.74304(5) A, c = 3.52542(6) A, Z = 1). Calculations suggest that LiNiN is a one-dimensional metal, as a result of the mixed pi- and sigma-bonding interactions between Ni and N along the c-axis. Solid-state 7Li NMR spectra are consistent with both fast Li+ motion and metallic behavior.

Ba2[Ni3N2]: a low-valent nitridonickelate-synthesis, crystal structure, and physical properties

The ternary alkaline-earth nitridonickelate Ba2[Ni3N2] (Ba2[NiI2Ni0N2]) was prepared by the reaction of mixtures of Ba2N and Ni in nitrogen gas of ambient back-pressure at 1173 K. The crystal structure determined by X-ray single-crystal and powder diffraction methods as well as from neutron diffraction data at various temperatures between 2 and 298 K is orthorhombic (Cmca (no. 64), 298 K: a=715.27(18) pm, b=1032.99(21) pm, c=740.12(20) pm) and provides the first example of a nitridonickelate with a two-dimensional complex anion. The Ni2 atom is described with a split position and the corresponding superstructure variants are investigated by theoretical full-potential nonorthogonal local-orbital calculations (FPLO). The average oxidation state of Ni in Ba2[Ni3N2] is +0.67, the lowest average value observed in nitridonickelates so far. Investigations of the physical properties demonstrate that Ba2[Ni3N2] acts as a "poor" metal with a large resistivity of approximately 2.7 mOmega cm at 300 K and exhibits low-dimensional magnetism with antiferromagnetic ordering at T approximately 90 K. XAS spectra correspond with low-valent Ni states.

Fast Lithium Ion Diffusion in the Ternary Layered Nitridometalate LiNiN

The structure, Li+ diffusion dynamics, and magnetic properties of the layered nitridonickelate(II), LiNiN, have been investigated by powder X-ray diffraction, 7Li solid-state NMR, and SQUID magnetometry and compared and contrasted with those of the Li+ fast ion conductor, Li3N. The replacement of Li+ by Ni2+ with concomitant generation of Li+ vacancies has profound effects on ionic diffusion and electronic properties. The nitridonickelate, akin to its binary parent, displays rapid Li+ ion diffusion but, by contrast, the diffusion process is confined only to the Li-N planes. Further, replacement of Li by Ni leads to a transition from semiconducting to metallic behavior, likely mediated through the creation of infinite, 1D Ni-N chains of increased covalency.

Evolution of structure, transport properties and magnetism in ternary lithium nitridometalates Li3−x−yMxN, M = Co, Ni, Cu

The structures, magnetism and ion transport properties of the ternary nitrides Li(3-x-y)M(x)N (M = Co, Ni, Cu; y= lithium vacancy) were examined by powder X-ray diffraction, solid-state NMR and SQUID magnetometry. Doping levels are achieved up to x approximately = 0.4 for M = Cu and Co, but much higher substitution levels (x approximately =1) are obtained in the Li-Ni-N system. Transition metals substitute for Li at the Li(1) interplanar site and the ensuing lithium vacancies are disordered within the [Li(2)N] planes. High substitution levels in the Li-Ni-N system lead to the formation of ordered phases. Diffusion parameters, including activation energies, correlation times and diffusion coefficients, were obtained from variable-temperature solid-state NMR measurements in several ternary compounds. SQUID magnetometry shows significant variations of the electronic properties with dopant and x. The properties of the ternary nitrides can be rationalised in terms of the identity of the dopant and the structural modifications arising from the substitution process.

Synthesis and Structure of the New Ternary Nitride SrTiN(2)

A new ternary nitride, SrTiN(2), has been synthesized by the solid-state reaction of Sr(2)N with TiN and characterized by powder X-ray diffraction. SrTiN(2) crystallizes in the tetragonal space group P4/nmm (a = 3.8799(2) Å, c = 7.6985(4) Å, Z = 2) and is isostructural with KCoO(2). Titanium is coordinated to five nitrogens in a distorted square-based pyramidal geometry, forming layers of edge-sharing pyramids which stack along the (001) direction. Strontium is situated between the Ti-N layers and is coordinated to five nitrogen atoms. The title compound is only the third example of a ternary titanium nitride.

The chemical bonding topology of ternary and quaternary transition metal nitrides containing low-coordinate metal atoms

Solid state ternary and quaternary metal nitrides containing a transition metal and one or two very electropositive metals such as alkali and (or) alkaline earth metals exhibit a number of structures containing low-coordinate transition metals in the transition metal – nitrogen subnetwork. Transition metal – nitrogen double and even triple bonds are found in these structures involving dπ → pπ bonding from a filled transition metal d orbital to an otherwise empty nitrogen p orbital. Such multiply bonded nitrogen atoms function as strong field ligands in contrast to amido ligands such as (Me3Si)2N−, which generally function as weak field ligands in transition metal chemistry. The transition metal environment in these ternary nitrides can be modelled by "banana bonds" from the polyhedron using the atomic orbitals required for both the σ- and π-bonding to the nitride ligands, e.g., the trigonal prism for the trigonal planar derivatives MIIIN36− (M = V, Cr, Mn, Fe) with three M=N double bonds as well as FeIIN24− in Li4FeIIN2 with two Fe≡N triple bonds and the planar square for the discrete linear CoIN25− in LiSr2CoN2. Reasonable electron counts are also obtained for the anionic metal–nitrogen networks in Ca2FeN2, Sr2LiFe2N3, Ba2LiFe2N3, Li3FeN2, CaNiN, Li3Sr3Ni4N4, BaNiN, and Ba8Ni6N7. Keywords: chemical bonding, topology, nitrides, transition metals.