Crystallographic, electronic and magnetic studies of Ce4Ni6Al23: a new ternary intermetallic compound in the cerium-nickel-aluminum phase diagram

The Al-rich portion of the ternary Ce-Ni-Al has been investigated and a new ternary phase of composition Ce₄Ni₆Al₂₃ has been found. This compound crystallizes in the monoclinic space group C2/m with the cell parameters a=16.042(8), b=4.140(4), c=18.380(8) Å and β=113.24(5)°. The structure has been determined by single crystal X-ray diffraction. The local environment of Ni and Ce is close to what is observed in the CeNi₂Al₅ and CeNiAl₄ structures. Band structure calculations, using the tight-binding-linear muffin-tin orbital-atomic-spheres approximation (TB-LMTO-ASA) method, have been performed to understand the electronic structure of Ce₄Ni₆Al₂₃ and the results are discussed in connection with those two other Ce-Ni-Al intermetallic compounds, which possess heavy-fermion behavior. Magnetic and heat capacity measurements have also been measured to analyze the low-temperature magnetic behavior of this new compound.     

Reinvestigation of the GaMn structure and theoretical studies of its electronic and magnetic properties

The crystal structure of the binary gallide compound GaMn is reinvestigated using X-ray diffraction. The structure is quite different from that proposed previously. Although GaMn is reported to crystallize with the Al₈Cr₅ structure type, space group R3m, we found that the centrosymmetric space group , with a=12.605(2) Å and c=8.0424(11) Å, was more accurate. Moreover, the atomic positions and the atomic displacement parameters, which are missing in the previous study, are now refined. Thereafter, band structure calculations have been performed using the TB-LMTO-ASA method to understand the electronic and magnetic properties of this compound. Analyses from the band structure, the density of states and the magnetic moments obtained using spin-polarized calculations show the stability of two different magnetic models relative to the nonmagnetic one.     

Ba14Zn5−xAl22+x: a new polar intermetallic compound with a novel 2D network

A new ternary, intermetallic compound, Ba₁₄Zn_5−xAl_22+x, was synthesized by heating the pure elements at 900°C. This compound crystallizes in the monoclinic space group I2/m, Z=2, with a=10.474(2) Å, b=6.0834(14) Å, c=34.697(8) Å and β=90.814(4)°. The crystal structure of Ba₁₄Zn_5−xAl_22+x consists of [Zn_5−xAl_22+x] slabs that are built with a novel, two-dimensional (2D) network of Zn and Al atoms involving eight-membered rings sandwiched between two layers of trigonal bipyramids interconnected by three-center bonding. Tight-binding, linear muffin-tin orbital (TB-LMTO-ASA) calculations have been performed to understand the relationship between composition and orbital interactions in the electronegative element framework. This new structure is closely related to the high-pressure, cubic Laves-type structure of BaAl₂ as well as the ambient pressure binary compound, Ba₇Al₁₃. The degree of valence electron charge transfer from the electropositive Ba atoms is related to the Al:Ba molar ratio in the Ba-Zn-Al system.     

Study on the cluster of floating dross before nucleating during hot-dipping process

At present, hot-dipping anticorrosion metalliccoating on the surface of steel base is the main methodto prevent atmospheric corrosion of steel. With thechange of atmospheric environment, the traditionalidea of hot-dipping pure Zn cladding already does not…     

Undistorted linear Bi chains with hypervalent bonding in La3TiBi5 from single‐crystal X‐ray diffraction

The crystal structure of the lanthanum titanium bismuthide La₃TiBi₅ (Pearson code hP18, Wyckoff sequence b d g2) has been established from single‐crystal X‐ray diffraction data and analyzed in detail using first‐principles calculations. There are no anomalies pertaining to the atomic displacement parameter of the Ti site, previously reported based on a powder X‐ray diffraction analysis of this compound. The anionic substructure contains columns of face‐sharing TiBi₆ octahedra and linear Bi chains. Due to a significant La(5d) and Bi(6p) orbital mixing, a perfectly one‐dimensional character of the Bi chains is not realised, while a three‐dimensional electronic structure is established instead. The latter fact explains the stability of the polyanionic pnictide units against Peierls distortions. The hypervalent bonding in the Bi chains is reflected in a rather long Bi—Bi distance of 3.2264 (4) Å and a typical pattern of bonding and antibonding interactions, as revealed by electronic structure calculations.     

Computational Cogitation of Cn@Al12 Clusters

A variety of novel C_nAl₁₂ core–shell nanoclusters have been investigated using density functional calculations. A series of C_n cores (n=1–4) have been encapsulated by icosahedral Al₁₂, with characteristic physical properties (energetics and stabilities, ionisation energies, electron affinities) calculated for each cluster. Other isomers, with the C_n moiety bound externally to the Al₁₂ shell, have also been studied. For both series, a peak in stability was found for n(C)=2, a characteristic that appears to be inextricably linked with the relaxation of the constituent parts upon dissociation. Analysis of trends for ionisation energies and electron affinities includes evaluation of contributions from the carbon and aluminium components, which highlights the effects of composition and morphology on cluster properties.     

Structure and electronic structure of quasicrystal and approximant surfaces: a photoemission study

The structure and electronic structure of different high-symmetry surfaces of either quasicrystalline or approximant Al–Pd–Mn were studied by means of photoemission-based techniques such as X-ray photoelectron diffraction (XPD) and ultraviolet photoelectron spectroscopy. We find that the twofold (2f), 3f and 5f surfaces of icosahedral Al–Pd–Mn exhibit all the symmetry elements of the icosahedral non-crystallographic group. These XPD experiments can be modeled by single-scattering cluster calculations.

The bulk-terminated icosahedral or approximant surfaces are recovered after ion sputtering followed by annealing at T≈500–600 °C. A wealth of ordered surface phases (with different compositions) are found after sputtering and depending on the annealing temperature as, for example, a crystalline bcc multitwinned phase (for T<400 °C) or a stable decagonal quasicrystalline surface (for T>650 °C).

The icosahedral surfaces are characterised by a lowering of the density of states close to the Fermi edge, compatible with the opening of a pseudogap, as expected for a quasicrystal. The crystalline overlayers are characterised by a sharp Fermi edge, while the approximant and decagonal quasicrystalline surfaces also have a lowered density of states.     

Züchtung und röntgenographische Untersuchung von Einkristallen des Alumothiosilicats Mn1,84Al0,16Si0,84Al0,16S4

Crystal Growth and Structure of the Alumothiosilicate Mn_1.84Al_0.16Si_0.84Al_0.16S₄ Single Crystals of the alumothiosilicate Mn_1.84Al_0.16Si_0.84Al_0.16S₄ were grown by chemical transport reaction. The compound represents the first example of this type of silicate. The crystals were characterized by electron microprobe analyses and X-ray methods. The compound crystallizes in the olivine type structure, space group Pnma, a = 1 266.9(2), b = 739.6(3), c = 592.8(1) pm. The mean bond lengths are very similar to those in Mn₂SiS₄. That part of aluminum which is situated at the octahedral sites is not equally distributed amongst both types of octahedral positions but is enriched on the smaller and more symmetric M(1) position.     

Hydroxyl‐Mediated Non‐oxidative Propane Dehydrogenation over VOx/γ‐Al2O3 Catalysts with Improved Stability

Supported vanadium oxides are one of the most promising alternative catalysts for propane dehydrogenation (PDH) and efforts have been made to improve its catalytic performance. However, unlike Pt‐based catalysts, the nature of the active site and surface structure of the supported vanadium catalysts under reductive reaction conditions still remain elusive. This paper describes the surface structure and the important role of surface‐bound hydroxyl groups on VO_x / γ‐Al₂O₃ catalysts under reaction conditions employing in situ DRIFTS experiments and DFT calculations. It is shown that hydroxyl groups on the VO_x /Al₂O₃ catalyst (V?OH) are produced under H₂ pre‐reduction, and the catalytic performance for PDH is closely connected to the concentration of V?OH species on the catalyst. The hydroxyl groups are found to improve the catalyst that leads to better stability by suppressing the coke deposition.     

A study of the phase Mg2Cu6Ga5, isotypic with Mg2Zn11. A route to an icosahedral quasicrystal approximant

The new title compound was synthesized by high-temperature means and its X-ray structure refined in the cubic space group Pm3macro, Z = 3, a = 8.278(1) A. The structure exhibits a 3-D framework made from a Ga(14) and Mg network within which large and small cavities are occupied by centered GaCu(12) icosahedral and Cu(6) octahedral clusters, respectively. The clusters are well bonded within the network. Electronic structure calculations show that a pseudogap exists just above the Fermi energy, and nearly all pairwise covalent interactions remain bonding over a range of energy above that point. Analysis suggests that the compound is hypoelectronic with a four-electron deficiency per unit cell, and such a derivative with Sc substituting for Mg is an appropriate quasicrystal approximant (Im3macro). Such characteristics seem to be key factors in the formation of icosahedral quasicrystals.     

Darstellung,Eigenschaften und Kristallstruktur von RuSn6[(Al1/3–xSi3x/4)O4]2 (0 ≤ x ≤ 1/3) – einem Oxid mit isolierten RuSn6‐Oktaedern

Preparation, Properties, and Crystal Structure of RuSn₆[(Al_1/3–xSi_3x/4)O₄]₂ (0 ≤ x ≤ 1/3) – an Oxide with isolated RuSn₆ Octahedra RuSn₆[(Al_1/3–xSi_3x/4)O₄]₂ is obtained by the solid state reaction of RuO₂, SnO₂, Sn, and Si in an Al₂O₃‐crucible at 1273 to 1373 K. The compound is cubic with the space group Fm 3 m (a = 9.941(1) Å, Z = 4, R₁ = 0.0277, wR₂ = 0.0619), a semiconductor and stable in air. Results of Mößbauer measurements as well as bond length‐bond strength calculations justify the ionic formulation Ru²⁺Sn₆²⁺[(Al_1/3–x³⁺Si_3x/4⁴⁺)O₄^2–]₂. The central motif of the crystal structure are separated RuSn₆‐octahedrea. These are interconnected by oxygen atoms, arranged tetrahedrely above the surfaces of the RuSn₆‐octahedrea and partialy filled with Al and Si, respectively. Because of these features the compound can be considered as a variant of the crystal structure type of pentlandite.     

Experimental and theoretical studies on bis[<Emphasis Type="Italic">μ</Emphasis>-2-methoxy-<Emphasis Type="Italic">N</Emphasis>′-(2-oxidobenzoyl)benzohydrazidato(3-)]dipyridinetricopper(II)

A novel homotrinuclear pyridine Schiff base copper(II) compound, [Cu₃(C₁₅H₁₁N₂O₄)₂(C₅H₅N)₂], has been synthesized and characterized by elemental analysis and X-ray single crystal deterimination. X-ray structural determination reveals that each copper(II) ion has a distorted square-planar geometry. The central copper ion is coordinated by two O and two N atoms from two Schiff base ligands, while each terminal copper ion is coordinated by one N and two O atoms of one Schiff base ligand and by one N atom of a pyridine molecule. Density funcational theory (DFT) method calculations of the structure, atomic charges distribution and natural bond orbital (NBO) analyses have been performed. The coordinate stabilization energies show that the trinuclear copper(II) compound is very stable.     

Direct Visualisation of the Surface Atomic Active Sites of Carbon-Supported Co3O4 Nanocrystals via High-Resolution Phase Restoration

The atomic arrangement of the terminating facets on spinel Co₃O₄ nanocrystals is strongly linked to their catalytic performance. However, the spinel crystal structure offers multiple possible surface terminations depending on the synthesis. Thus, understanding the terminating surface atomic structure is essential in developing high-performance Co₃O₄ nanocrystals. In this work, we present direct atomic-scale observation of the surface terminations of Co₃O₄ nanoparticles supported on hollow carbon spheres (HCSs) using exit wavefunction reconstruction from aberration-corrected transmission electron microscopy focal-series. The restored high-resolution phases show distinct resolved oxygen and cobalt atomic columns. The data show that the structure of {100}, {110}, and {111} facets of spinel Co₃O₄ exhibit characteristic active sites for carbon monoxide (CO) adsorption, in agreement with density functional theory calculations. Of these facets, the {100} and {110} surface terminations are better suited for CO adsorption than the {111}. However, the presence of oxygen on the {111} surface termination indicates this facet also plays an essential role in CO adsorption. Our results demonstrate direct evidence of the surface termination atomic structure beyond the assumed stoichiometry of the surface.     

Origin of pressure-induced insulator-to-metal transition in the van der Waals compound FePS3 from first-principles calculations

Pressure-induced insulator-to-metal transition (IMT) has been studied in the van der Waals compound iron thiophosphate (FePS₃) using first-principles calculations within the periodic linear combination of atomic orbitals method with hybrid Hartree–Fock-DFT B3LYP functional. Our calculations reproduce correctly the IMT at ∼15 GPa, which is accompanied by a reduction of the unit cell volume and of the vdW gap. We found from the detailed analysis of the projected density of states that the 3p states of phosphorus atoms contribute significantly at the bottom of the conduction band. As a result, the collapse of the band gap occurs due to changes in the electronic structure of FePS₃ induced by relative displacements of phosphorus or sulfur atoms along the c-axis direction under pressure.     

Exploration of the lithium–aluminum–silver system. Crystal and electronic structure analysis of new phases Li6.98Al4.15Ag0.87 and LiAlAg2

The lithium–aluminum–silver ternary system has been investigated and two new phases Li_6.98Al_4.15Ag_0.87 and LiAlAg₂ were characterized using both powder and single crystal X-ray diffraction techniques. These phases crystallize in the cubic system, space group (a=6.344(1), 6.3124(5) Å), they, respectively, display the Pearson's cF12- and cF16-type structural arrangements. Compared to Li₂AlAg, the only phase in the system reported so far, the structure of Li_6.98Al_4.15Ag_0.87 is disordered owing to atomic substitutions and contains a full site vacancy. Band structures and densities of states of Li_6.98Al_4.15Ag_0.87, LiAlAg₂ and Li₂AlAg have been calculated by a first principle pseudopotential method using the plane-wave basis CASTEP package.     

Direct determination of a topmost atomic layer of (100) surfaces on (La0.3Sr0.7)(Al0.65Ta0.35)O3 single crystals annealed in air by high-resolution scanning transmission electron microscopy

Herein, we investigated the surface of an (La_0.3Sr_0.7)(Al_0.65Ta_0.35)O₃ (LSAT) single crystal via scanning transmission electron microscopy (STEM) after annealing in air. We found amorphous mounds and atomically flat surfaces formed on the surface of the (100) LSAT single crystal subsequent to heat treatment. These surface mounds mainly constituted SrO, including ~50 at.% Al. The atomically flat surface showed a B-site termination determined by the direct surface observation at the atomic scale through HAADF-STEM. The atomic arrangements on the surface were accommodated by surface-mound formation and La evaporation. Consequently, the ordered structure disappeared because of the increase in the Ta content at the terminated B-site layer.     

RbBrF4 Revisited

Rubidium tetrafluoridobromate(III) was synthesized and structurally characterized. The compound is isotypic to sodium and potassium tetrafluoridobromate(III), and crystallizes in the tetragonal space group I4/mcm (tI24, KBrF₄ structure type) with a = 6.3718(2), c = 11.4934(3) Å, V = 466.63(2) ų, Z = 4, at T = 293 K. Additionally we investigated the compound by means of IR and Raman spectroscopy as well as theoretical studies. The data obtained by quantum chemical calculations confirm the crystal structure, and also the atomic distances and angles with an average deviation of 2.2 to 2.7 %.     

Li9Al4Sn5 as a new ordered superstructure of the Li13Sn5 type

Alloys from the ternary Li–Al–Sn system have been investigated with respect to possible applications as negative electrode materials in Li‐ion batteries. This led to the discovery of a new ternary compound, a superstructure of the Li₁₃Sn₅ binary compound. The ternary stannide, Li₉Al₄Sn₅ (nonalithium tetraaluminium pentastannide; trigonal, P m 1, hP18 ), crystallizes as a new structure type, which is an ordered variant of the binary Li₁₃Sn₅ structure type. One Li and one Sn site have m . symmetry, and all other atoms occupy sites of 3m . symmetry. The polyhedra around all types of atoms are rhombic dodecahedra. The electronic structure was calculated by the tight‐binding linear muffin‐tin orbital atomic spheres approximation method. The electron concentration is higher around the Sn and Al atoms, which form an [Al₄Sn₅]^m− polyanion.     

Quantum-chemical,spectroscopic and X-ray diffraction studies on nickel complex of 2-hydroxyacetophenone thiosemicarbazone with triphenylphospine

Reaction of 2-hydroxyacetophenone thiosemicarbazone with [Ni(PPh₃)₂Cl₂] in optimized conditions afforded a mixed ligand complex with an isolated triphenylphosphine molecule. The structure was characterized by elemental analysis, IR, NMR and UV–Vis. spectroscopies and single crystal X-ray diffraction technique. In addition, the molecular geometry, vibrational frequencies and gauge including atomic orbital (GIAO) ¹H and ¹³C NMR chemical shift values of the title compound in the ground state have been calculated using the density functional theory (DFT/B3LYP) method with the 6-31G(d,p) basis set for the C, N, O, S, P, H atoms and LANL2DZ pseudo-potential for the Ni atom, and compared with the experimental data. Besides, atomic charge distributions, molecular electrostatic potential and frontier molecular orbitals (FMO) analysis of the title compound were investigated by theoretical calculations. The thermodynamic properties of the compound at different temperatures have been calculated and corresponding relations between the properties and temperature have also been obtained. Atomic charge distributions indicate that during forming the title compound, the free ligand of thiosemicarbazone ion transfers their negative charges to central Ni(II) ion. The effect of different solvents (chloroform, methanol and water) on the geometry, vibrational frequencies, total energies and dipole moments was studied using the density functional theory (DFT/B3LYP) method by applying the Onsager and the Polarizable Continuum Model (PCM).     

Electronic tuning of Mg2Cu6Ga5. A route to crystalline approximant and quasicrystalline phases

Studies of Mg2Cu6Ga5 reveal that this compound contains incomplete Bergman clusters in its structure and shows a pseudogap and empty bonding states just above the Fermi energy according to band calculations. Under a rigid band assumption, such a compound may be tuned to approximant and quasicrystal phases in which the required number of electrons are attained. Here, we replace part of Mg in the isotypic Mg2Cu6Ga5 with Sc, and both 1/1 approximant and icosahedral quasicrystal phases are obtained after some fine-tuning. This method closely correlates the pseudogap and bonding with Hume-Rothery concepts, thus giving useful directions for future quasicrystal searches, especially when approximants are not known.