Superhard materials (Vickers hardness >40 GPa) are the key to demanding materials processing in industry scale and synthesis via high pressure routes like in diamond anvil cells. Despite extensive research both by experiments and computational chemistry, synthetic diamond (Vickers hardness H-V approximate to 90 GPa) is still widely used. Sharing metastability and structure with diamond, softer cubic boron nitride cBN (H-V approximate to 60 GPa) found application as e.g. refractory material where diamond lacks chemical resistance. This is most prominent in contact with iron containing compounds, ruling out diamond-coated machining tools for steels. While there are improvements of those materials like grain and grain boundary optimizations, none has reached wider industrial application due to processing difficulty and costs. Based on the tetragonal coordination of diamond and cBN, the present work addresses the question of novel superhard materials from the class of carbonitrides CxNy and its analogues from Group IVA. A novel family of hexagonal A(4)N(4) structures with A = C, Si, Ge is proposed based on crystal chemistry considerations and structure optimizations using Density Functional Theory with the Generalized Gradient Approximation. The structures are characterized by {A(2)N(2)} bilayers of AN polyhedra separated by repulsive N-N interactions. Due to short covalent bonds, the carbonitride is predicted to classify as superhard material. Ab initio calculations indicate thermodynamically and dynamically stable C4N4 at ambient conditions, laying the foundation for successful synthesis at p > 40 GPa in the future.

Human activity has an ever-increasing impact on the environment. In order to understand all processes and interactions behind this change, one has to analyze the environmental impact. Life Cycle Assessments (LCAs) are one way to achieve this, which, however, are time-consuming and often associated with high costs, as well as the requirement of specialized knowledge and software. This paper introduces a model, which allows an initial assessment. The model enables a more pragmatic way and may be considered as a first step in order to implement ecological sustainability considerations into companies. Based on a real-world problem, namely the disposal of foundry dust, the model is explained in a vivid manner.

Our discovery of half metal ferromagnetic (HFM) properties on shandite type Co 3 Sn 2 S 2 =Sn 2 Co 3 S 2 about 20 years ago by DFT calculations opened the gate for fascinating discoveries like giant anomalous Hall effect and Weyl semimetal characteristics. Thereby, interest arose on electronic and magnetic structure effects upon substitution of M=Co and A=Sn sites in and between Co Kagomé layers. Non isoelectronic substitution to A =In or M =Ni causes a decay of magnetic properties to semiconducting diamagnetic InSnCo 3 S 2 or paramagnetic semi metal Ni 3 Sn 2 S 2 . The present study addresses simultanious substitutions on both A and M sites to novel isoelectronic compounds of Co 3 Sn 2 S 2 . Therefore, DFT calculations were performed on model structures MM' 2 AA'X 2 ( M =Fe, Co, Ni; A =In, Sn, Sb; X =S). By the given approach, target compositions are identified that are interesting for future investigations and discoveries.

Topological Weyl semimetals have recently attracted considerable attention among materials scientists as their properties are predicted to be protected against perturbations such as lattice distortion and chemical substitution. However, any experimental proof of such robustness is still lacking. In this study, we experimentally demonstrate that the topological properties of the ferromagnetic kagomé compound Co3Sn2S2 are preserved upon Ni substitution. We systematically vary the Ni content in Co3Sn2S2 single crystals and study their magnetic and anomalous transport properties. For the intermediate Ni substitution, we observe a remarkable increase in the coercive field while still maintaining significant anomalous Hall conductivity. The large anomalous Hall conductivity of these compounds is intrinsic, consistent with first-principles calculations, which proves its topological origin. Our results can guide further studies on the chemical tuning of topological materials for better understanding.

We report experimental and theoretical evidence that GaGeTe is a basic Z2 topological semimetal with three types of charge carriers: bulk-originated electrons and holes as well as surface state electrons. This electronic situation is qualitatively similar to the classic 3D topological insulator Bi2Se3, but important differences account for an unprecedented transport scenario in GaGeTe. High-resolution angle-resolved photoemission spectroscopy combined with advanced band structure calculations show a small indirect energy gap caused by a peculiar band inversion at the T-point of the Brillouin zone in GaGeTe. An energy overlap of the valence and conduction bands brings both electron and holelike carriers to the Fermi level, while the momentum gap between the corresponding dispersions remains finite. We argue that peculiarities of the electronic spectrum of GaGeTe have a fundamental importance for the physics of topological matter and may boost the material’s application potential.

A new preparation route is developed for the synthesis of needle-like crystals of [Au(S2 CNH2 )2 ]SCN, which avoids disproportionation of the AuI salt used as a starting material. In the crystal structure, the two crystallographically independent AuIII centers are in a square-planar environment of two S2 CNH2 ligands. The Hirshfeld surface analysis reveals the presence of noncovalent intermolecular S⋅⋅⋅S interactions, which are essential for the spatial arrangement of the molecules. Density functional theory (DFT) calculations including dispersion and damping corrections result in a unit cell volume very close to the value determined experimentally. Thermal decomposition in an inert atmosphere generates black needles with lengths of up to 500 μm. X-ray powder diffraction and pair distribution function analyses demonstrate that the needles are composed of nanosized crystals with a volume-weighted average domain size of 20(1) nm. According to results of X-ray photoemission experiments, the black needles are covered by a nitrogen-rich carbon nitride with composition near (CN)2 N. 13 C solid-state NMR investigations indicate that two different carbon species are present, with signals corresponding well to heptazine units as in melon and triazine units as in poly(triazin imide) type compounds. Scanning transmission electron microscopy tomography evidences that the needles are composed of slightly elongated nanoparticles.

AbstractParallel angeordnete Spins in Cobalt‐Kagome‐Netzen lassen Forscher gleich mehrfach jubeln: Liu et al. und Wang et al. berichten von Entdeckungen einmaliger Eigenschaftskombinationen: Sn2Co3S2=Co3Sn2S2=SnCo3/2S weist riesige anomale Hall‐Effekte auf, die bisher bekannte Materialien um Größenordnungen übertreffen. Für die einstige Laborkuriosität wird dies auf eine elektronische Topologie des 2001 vorhergesagten magnetischen S= ‐Grundzustands zurückgeführt, die es zu einem herausragenden Beispiel eines magnetischen Weyl‐Halbmetalls macht. Wir geben einen chemischen Blick auf diese lange Zeit wenig verstandene Verbindung, die auch im Hinblick auf Skyrmionen‐Gitter und als Thermoelektrikum erforscht wird.

Herein, the crystal structure as well as second‐harmonic‐generation (SHG), thermal and spectroscopic properties of Sn[B 2 O 3 F 2 ] (TFB = tin‐fluorooxo‐borate) are presented. TFB adopts a novel non‐centrosymmetric crystal structure, which is determined by single‐crystal X‐ray diffraction (XRD) ( P 31 m , Z = 1, a = 4.5072(2) Å, c = 4.7624(3) Å) and comprises [B 2 O 3 F 2 ] 2− layers consisting solely of BO 3 F tetrahedra; the covalent BF bonds are unequivocally localized via solid‐state NMR spectroscopy as well as density functional theory (DFT) calculations. TFB is insensitive to air and moisture, shows a stronger SHG intensity than K[H 2 PO 4 ] (KDP) and a bandgap of ≈5 eV. The thermal decomposition yields two new borate fluorides.

La2NiBi was synthesized by heating a cold pressed pellet of the elements in a sealed and evacuated silica tube at 1070 K. The structure was determined via powder and single crystal X‐ray diffraction. La2NiBi crystallizes orthorhombically, in the space group Pnma: a = 838.88(6), b = 455.61(11), c = 1210.4(2) pm and V = 0.46261(14) nm3 (wR = 0.1002, 1001 F2 values, 26 variables, Z = 4). La2NiBi represents a higher congener of La2NiSb and adopts a ternary ordered version of the Bi3Ni structure type. Similar to La2NiSb, the nickel atoms form infinite zigzag chains (259 pm Ni–Ni) with trigonal‐prismatic lanthanum coordination. One rectangular face of the lanthanum prism is capped by a bismuth atom (333.08–364.74 pm La–Bi, 281.18 pm Ni–Bi). These zigzag chains run along the b axis. DFT based band structure calculations and DOS representations suggest metallic behavior. This was confirmed via temperature dependent impedance spectroscopic measurements. A Seebeck coefficient of –10 μV·K–1 in the temperature range up to 873 K substantiates this finding. Thermal analyses show that the compound is stable up to 873 K under inert gas conditions and degrades at higher temperatures. The magnetic measurements show almost no grain boundary nickel impurities characterizing La2NiBi as a weak Pauli paramagnet.

Phosphorus, first found in the seventeenth century, played an important role in the definition of the element term by Lavoisier and thus shaped the beginning of the era of modern chemistry. It was discovered for the first time in the most unstable crystalline modification—the white phosphorus. Today, a variety of experimentally proven allotropes are known. The most common allotropes, such as black, violet, and fibrous phosphorus, are described here with respect to their synthesis, crystal structures, thermal, and thermodynamic properties. Besides, more than 50 crystalline allotropes have been predicted, and their stabilities have been estimated using quantum‐chemical methods. This way, phosphorus becomes one of the most structurally variable elements of the periodic table. In this article, some of the most reasonable and sophisticated calculations are presented. The applications of elemental phosphorus are mainly connected with its semiconducting properties. Thus, the development of current applications is strongly related to new synthesis methods for direct preparation of individual, phase pure allotropic forms of phosphorus. The past decade supplied basic results on the formation of black phosphorus and other modifications, primarily using the mineralizer concept. Related to graphene and other two‐dimensional, layered structures, phosphorene is of drastically rising interest. The pertinent modifications are characterized by corrugated arrangement of six‐membered P‐rings, where both the boat conformation and the chair conformation are known. The application of phosphorene is in a jumping evolution. Currently, phosphorene is already in use in manifold ways, including as a sensor, optical device, transistor, energy‐conversion material, and supercapacitor material.

Parallelly aligned spins in Co-Kagome nets have provided several reasons for researchers to celebrate: Liu et al. and Wang et al. have reported discoveries of unique combinations of properties: Sn2Co3S2=Co3Sn2S2=SnCo3/2S exhibits giant anomalous Hall effects that exceed those of known materials by orders of magnitude. For this laboratory curiosity, a specific electronic topology has been discovered in the predicted half-metal ferromagnetic S=1/2 state that makes it a fascinating example of the novel group of magnetic Weyl semimetals. We present a chemical view on this compound that was little understood for a long time, but that is now also studied with respect to skyrmion lattices and thermoelectrics.

The very first alkaline-earth fluorooxoborate Ba[B4 O6 F2 ] was synthesised by solid state methods starting from Ba(BF4 )2 , β-BaB2 O4 , and B2 O3 . The crystal structure derived from single-crystal X-ray diffraction (P21 /n, a=6.6384(2) Å, b=7.6733(3) Å, c=11.3385(4) Å, β=91.281(2)°, Z=4, Rint =0.0269, R1 =0.018, wR2 =0.034) comprises layers of BO3 F tetrahedra condensed through triangular BO3 units according to the descriptor 2Δ2□:Δ. The extraordinary thirteen-fold coordination of barium by oxygen and fluorine leads to interesting optical properties of a sample doped with divalent europium, where a 4f→4f emission was recorded around 359 nm together with a broad emission band of a 5d→4f emission peaking at 366 nm. The compound is further characterised by IR-, Raman-, and solid-state NMR-spectroscopic methods. Moreover, DFT calculations as well as TGA and DSC measurements were performed.

γ-NiB4O7 was synthesized in a high-pressure/high-temperature experiment at 5 GPa and 900 °C. The single-crystal structure analysis yielded the following results: space group P6522 (No. 179), a = 425.6(2), c = 3490.5(2) pm, V = 0.5475(2) nm3, Z = 6, and Flack parameter x = -0.010(5). Second harmonic generation measurements confirmed the acentric crystal structure. Furthermore, γ-NiB4O7 was characterized via vibrational as well as single-crystal electronic absorption spectroscopy, magnetic measurements, high-temperature X-ray diffraction, differential scanning calorimetry, and thermogravimetry. Density functional theory-based calculations were performed to facilitate band assignments to vibrational modes and to evaluate the elastic properties and phase stability of γ-NiB4O7.

Abstract We report on microsecond-resolved in-situ SAXS experiments of the early nucleation and growth behavior of both cadmium sulfide (CdS) quantum dots in aqueous solution including the temperature dependence and of gold (Au) nanoparticles. A novel free-jet setup was developped to access reaction times as early as 20 μs. As the signal in particular in the beginning of the reaction is weak the containment-free nature of this sample environment prooved crucial. The SAXS data reveal a two-step pathway with a surprising stability of a structurally relaxed cluster with a diameter of about 2 nm. While these develop rapidly by ionic assembly, a further slower growth is attributed to cluster attachment. WAXS diffraction confirms, that the particles at this early stage are not yet crystalline. This growth mode is confirmed for a temperature range from 25°C to 45°C. An energy barrier for the diffusion of primary clusters in water of 0.60 eV was experimentally observed in agreement with molecular simulations. To access reaction times beyond 100 ms, a stopped-drop setup -again contaiment- free is introduced. SAXS experiments on the growth of Au nanoparticles on an extended time scale provide a much slower growth with one population only. Further, the influence of ionizing X-ray radiation on the Au particle fromation and growth is discussed.

Anionic layers in CsGaS2undergo a transition to infinite strands at high temperature and transfer back under pressure.

Two fields are united in Mo2B4O9, the first borate compound incorporating transition-metal clusters into its crystal structure. It thus constitutes the hitherto unknown interface between two previously separated fields of research—borate and metal cluster chemistry. In their Communication on page 6449 ff., H. Huppertz and co-workers show how the planned reduction of a reagent in a high-pressure experiment smoothed the way to this novel substance class. Two fields are united in Mo2B4O9, the first borate compound incorporating transition-metal clusters into its crystal structure. It thus constitutes the hitherto unknown interface between two previously separated fields of research—borate and metal cluster chemistry. In their Communication on page 6449 ff., H. Huppertz and co-workers show how the planned reduction of a reagent in a high-pressure experiment smoothed the way to this novel substance class. Dipeptide Structures Molecular Recognition Heterocylces

We report on the first thoroughly characterized molybdenum borate, which was synthesized in a high-pressure/high-temperature experiment at 12.3 GPa/1300 °C using a Walker-type multianvil apparatus. Mo2 B4 O9 incorporates tetrahedral molybdenum clusters into an anionic borate crystal structure-a structural motif that has never been observed before in the wide field of borate crystal chemistry. The six bonding molecular orbitals of the [Mo4 ] tetrahedron are completely filled with 12 electrons, which are fully delocalized over the four molybdenum atoms. This finding is in agreement with the results of the magnetic measurements, which confirmed the diamagnetic character of Mo2 B4 O9 . The two four-coordinated boron sites can be differentiated in the 11 B MAS-NMR spectrum because of the strongly different degrees of local distortions. Experimentally obtained IR and Raman bands were assigned to vibrational modes based on DFT calculations.

Within carbon suboxide C2O devised from ab initio in ground state two-dimensional structure, finite spin polarization is demonstrated, leading to a stable ferromagnetic order confirmed for simple and superstructure cells. Specifically structural relaxation of C2O in 2D AlB2-type structure shows that the hexagonal crystal symmetry is maintained with a large c/a ratio letting magnetization develop on oxygen p valence states. Band-like O-px,y and localized-like O-pz spin projected density of states show striking resemblance with Cr-d in well known room temperature CrO2 ferromagnet with band gap opening in majority spin states leading to an integer magnetic moment of 2μB and a strongly ferromagnetic behavior in the ground state.

Mo2B4O9 vereint zwei Forschungsfelder – Boratchemie und Metallcluster –, denn es ist das erste Borat, das Übergangsmetallcluster in der Kristallstruktur enthält. Wie H. Huppertz und Mitarbeiter in ihrer Zuschrift auf S. 6549 zeigen, ebnete ein gezielter Reduktionsprozess in einem Hochdruckexperiment den Weg zu dieser neuen Substanzklasse. Mo2B4O9 vereint zwei Forschungsfelder – Boratchemie und Metallcluster –, denn es ist das erste Borat, das Übergangsmetallcluster in der Kristallstruktur enthält. Wie H. Huppertz und Mitarbeiter in ihrer Zuschrift auf S. 6549 zeigen, ebnete ein gezielter Reduktionsprozess in einem Hochdruckexperiment den Weg zu dieser neuen Substanzklasse. Dipeptidstrukturen Geodätische Kohlenwasserstoffe Heterocyclen

Inspired by the synthesis of the first atomic-scale double-helix semiconductor SnIP, this study deals with the question of whether more atomistic, inorganic double-helix compounds are accessible. With the aid of quantum chemical calculations, we have identified 31 candidates by a homoatomic substitution in MXPn, varying the Group 14 M-element from Si to Pb, the Group 17 X-element from F to I and replacing the pnictide (Pn) phosphorus by arsenic. The double-helical structure of SnIP has been used as the starting model for all candidates and the electronic structure and vibrational spectra were determined within the framework of density functional theory (DFT). Varying the outer MX or the inner Pn helix led to the conclusion that iodide- and bromide-containing MXPn compounds show similar structures to SnIP. Here, the calculations indicate interesting effects for electronic band-gap tuning. For the highly polarized fluorides, a segregation of the helices to more complex MX substructures is predicted.