Nonaqueous Synthesis of Low-Vacancy Chromium Hexacyanochromate.

Prussian blue analogues (PBAs) are a highly tunable family of materials with properties suitable for a wide variety of applications. Although their straightforward aqueous synthesis allows for the facile preparation of a diverse set of compositions, the use of water as the solvent has hindered the preparation of specific compositions with highly sought-after properties. A typical example is Cr[Cr(CN)]: its predicted strong magnetic interactions have motivated many attempts at its synthesis but with limited success.

Possible Superconductivity for Layered Metal Boride Carbide Compounds MBC (M = Alkali, Alkaline-Earth, or Rare-Earth Metals).

The possible emergence of superconductivity in layered metal boride carbide compounds MBC (M = Sc, Y, Be, Ca) was investigated using density functional theory calculations upon the topology of a boron-carbon network and the nature of the metal. ScBC and YBC show metallic and superconductive properties with low critical temperatures (s). The semiconducting BeBC compound may show superconductivity upon carrier doping with a high of 47.

Is the protactinium(V) mono-oxo bond weaker than what we thought?

The bond distance is the simplest and most obvious indicator of the nature of a given chemical bond. However, for rare chemistry, it may happen that it is not yet firmly established. In this communication, we will show that the formally-triple protactinium(V) mono-oxo bond is predicted to be longer than what was previously reported in the solid state and in solution, based on robust quantum mechanical calculations, supported by an extensive methodological study.

Spin-Reorientation-Driven Linear Magnetoelectric Effect in Topological Antiferromagnet Cu_{3}TeO_{6}.

The search for new materials for energy-efficient electronic devices has gained unprecedented importance. Among the various classes of magnetic materials driving this search are antiferromagnets, magnetoelectrics, and systems with topological spin excitations. Cu_{3}TeO_{6} is a material that belongs to all three of these classes.

Ionic Conductivity and Structure of Glasses Synthesized by Mechanical-Milling Methods in the [NaS]-(100 - ) [0.5GeS-0.5GaS] System.

Chalcogenide glasses in the NaS-GeS-GaS pseudoternary system were synthesized using a combination route of melt-quenching and mechanical-milling methods. First, a glass rich in germanium (90GeS-10GaS) is synthesized by melt-quenching synthesis in a silica tube sealed under vacuum. This glass is used as a precursor for the second step of mechanochemistry to explore the NaS-GeS-GaS pseudoternary system.

Eu- and Tb-adsorbed SiN and GeN: tuning the colours with one luminescent host.

Phosphor-converted white light emitting diodes (pc-LEDs) are efficient light sources for applications in lighting and electronic devices. Nitrides, with their wide-ranging applicability due to their intriguing structural diversity, and their auspicious chemical and physical properties, represent an essential component in industrial and materials applications. Here, we present the successful adsorption of Eu and Tb at the grain boundaries of bulk β-SiN and β-GeN by a successful combustion synthesis.

Structural Characterization and Influence of Defects on the Optical Properties of the Oxygen-Deficient Perovskite BaLiNbO□.

A new oxygen-deficient perovskite BaLiNbO□ was synthesized via a conventional solid-state route and compared to the already known perovskite BaLiNbO. The structure of BaLiNbO□ was investigated by means of X-ray and neutron diffraction, TEM, NMR, and XPS. The study of its thermal behavior revealed an unexpected color change when heated to 1400 °C in a sealed platinum tube, with conservation of the initial X-ray structure.

Unveiling electronic and magnetic properties of Cu(SeO)Cland Cu(TeO)Broxohalide systems via first-principles calculations.

Here, we report a theoretical investigation of the electronic and magnetic properties of two oxohalide compounds, namely Cu(SeO)Cland Cu(TeO)Br, using density functional theory (DFT). These layered systems are characterized by two inequivalent Cu sites, with CuOand CuO(= Cl, Br) environments, respectively. A new magnetic model is proposed through the calculation of the magnetic exchange couplings.

Crystal, electronic and magnetic structures of a novel series of intergrowth carbometalates RCoC (R = Y, Gd, Tb).

A series of new ternary isostructural RCoC (R = Y, Gd, Tb) carbides was synthesized by annealing of arc-melted stoichiometric samples. The crystal structure of TbCoC [space group P2/m, Pearson symbol mP18, a = 12.754(2) Å, b = 3.

Thermodynamic Evidence of Proximity to a Kitaev Spin Liquid in Ag_{3}LiIr_{2}O_{6}.

Kitaev magnets are materials with bond-dependent Ising interactions between localized spins on a honeycomb lattice. Such interactions could lead to a quantum spin-liquid (QSL) ground state at zero temperature. Recent theoretical studies suggest two potential signatures of a QSL at finite temperatures, namely, a scaling behavior of thermodynamic quantities in the presence of quenched disorder, and a two-step release of the magnetic entropy.

Electronic properties of Pb-I deficient lead halide perovskites.

The electronic structure evolution of deficient halide perovskites with a general formula (A,A')MX was investigated using the density functional theory. The focus is placed on characterization of changes in the bandgap, band alignment, effective mass, and optical properties of deficient perovskites at various concentrations of defects. We uncover unusual electronic properties of the defect corresponding to a M-X vacancy filled with an A' cation.

Experimental and Theoretical Investigation of the Anti-Ferromagnetic Coupling of Cr Ions through Diamagnetic -O-Nb-O- Bridges.

The synthesis and properties of a novel hetero-tetranuclear compound [Cr(bpy)(μ-O)Nb(CO)]·3HO (1; bpy = 2,2'-bipyridine), investigated by single-crystal X-ray diffraction, magnetization measurements, IR, UV/visible spectroscopy, electron paramagnetic resonance (EPR; X- and Q-bands and high-field), and density functional theory (DFT) calculations, are reported. Crystal structure of 1 (orthorhombic Pcab space group) consists of a square-shaped macrocyclic {Cr(μ-O)Nb} core in which Cr and Nb ions are alternately bridged by oxo ions and three uncoordinated water molecules. The intramolecular Cr···Cr distances through the -O-Nb-O- bridges are 7.

Spectromicroscopy of C and azafullerene CN: Identifying surface adsorbed water.

C fullerene crystals may serve as important catalysts for interstellar organic chemistry. To explore this possibility, the electronic structures of free-standing powders of C and (CN) azafullerenes are characterized using X-ray microscopy with near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy, closely coupled with density functional theory (DFT) calculations. This is supported with X-ray photoelectron spectroscopy (XPS) measurements and associated core-level shift DFT calculations.

Predicting experimentally stable allotropes: Instability of penta-graphene.

In recent years, a plethora of theoretical carbon allotropes have been proposed, none of which has been experimentally isolated. We discuss here criteria that should be met for a new phase to be potentially experimentally viable. We take as examples Haeckelites, 2D networks of sp(2)-carbon-containing pentagons and heptagons, and "penta-graphene," consisting of a layer of pentagons constructed from a mixture of sp(2)- and sp(3)-coordinated carbon atoms.

Thermochromism in yttrium iron garnet compounds.

Polycrystalline yttrium iron garnet (Y3Fe5O12, hereafter labeled YIG) has been synthesized by solid-state reaction, characterized by X-ray diffraction, Mössbauer spectroscopy, and UV-vis-NIR diffuse reflectance spectroscopy, and its optical properties from room temperature (RT) to 300 °C are discussed. Namely, its greenish color at RT is assigned to an O(2-) → Fe(3+) ligand-to-metal charge transfer at 2.57 eV coupled with d-d transitions peaking at 1.

Atomic configuration of nitrogen-doped single-walled carbon nanotubes.

Having access to the chemical environment at the atomic level of a dopant in a nanostructure is crucial for the understanding of its properties. We have performed atomically resolved electron energy-loss spectroscopy to detect individual nitrogen dopants in single-walled carbon nanotubes and compared with first-principles calculations. We demonstrate that nitrogen doping occurs as single atoms in different bonding configurations: graphitic-like and pyrrolic-like substitutional nitrogen neighboring local lattice distortion such as Stone-Thrower-Wales defects.

Room-temperature spin-spiral multiferroicity in high-pressure cupric oxide.

Multiferroic materials, in which ferroelectric and magnetic ordering coexist, are of fundamental interest for the development of multi-state memory devices that allow for electrical writing and non-destructive magnetic readout operation. The great challenge is to create multiferroic materials that operate at room temperature and have a large ferroelectric polarization P. Cupric oxide, CuO, is promising because it exhibits a significant polarization, that is, P~0.

Multinuclear (67Zn, 119Sn and 65Cu) NMR spectroscopy--an ideal technique to probe the cationic ordering in Cu2ZnSnS4 photovoltaic materials.

For the very first time, (67)Zn, (119)Sn and (65)Cu NMR investigations have been carried out on Cu2ZnSnS4 derivatives (CZTS) for photovoltaic applications. NMR spectroscopy is shown to be sensitive enough to probe the Cu/Zn disorder within the kesterite structure of the studied compounds. In addition, reference spectra of Cu2ZnSnS4 are provided, and experimental (67)Zn and (65)Cu parameters are compared with ab initio calculations.

Theoretical investigation of the magnetic exchange interactions in copper(II) oxides under chemical and physical pressures.

It remains a challenge to understand the unconventional mechanisms that cause high-T(C) superconductivity in cuprate superconductors, high-T(C) multiferroicity in CuO, or low-dimensional magnetism in the spin-Peierls transition compounds such as CuGeO(3). A common feature of all these copper oxide compounds (containing Cu(2+) ions) is the presence of large magnetic superexchange interactions J. It is a general strategy to apply chemical and/or physical pressure in order to tune these exotic properties.

NMR parameters in alkali, alkaline earth and rare earth fluorides from first principle calculations.

(19)F isotropic chemical shifts for alkali, alkaline earth and rare earth of column 3 basic fluorides are measured and the corresponding isotropic chemical shieldings are calculated using the GIPAW method. When using the PBE exchange-correlation functional for the treatment of the cationic localized empty orbitals of Ca(2+), Sc(3+) (3d) and La(3+) (4f), a correction is needed to accurately calculate (19)F chemical shieldings. We show that the correlation between experimental isotropic chemical shifts and calculated isotropic chemical shieldings established for the studied compounds allows us to predict (19)F NMR spectra of crystalline compounds with a relatively good accuracy.

Resolving the aluminum ordering in aluminosilicates by a combined experimental/theoretical study of 27Al electric field gradients.

The discrimination between atomic species in light-element materials is a challenging question. An archetypal example is the resolution of the Al/Si ordering in aluminosilicates. Only an average long-range order can be deduced from powder X-ray or neutron diffraction, while magic-angle-spinning NMR provides an accurate picture of the short-range order.

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.