Search

Nanocrystals of the CrCl3–RuCl3 solid solution are deposited onto a substrate and directly delaminated to obtain few- and monolayer structures.

In the search for novel 2D materials with potentially valuable properties, such as a tunable band gap for optoelectronic or catalytic applications, solid solutions hold the potential to significantly expand the inventory of available 2D nanomaterials. In this study, we present for the first time the synthesis of such 2D rhodium trihalide solid solutions: RhBr x Cl3−x and RhBr x I3−x . We use thermodynamic simulations and simultaneous thermal analysis to predict conditions for their rational synthesis and to investigate suitable chemical vapor transport (CVT) parameters for these solid solutions. The evolution of the lattice parameters was investigated by powder x-ray diffraction, showing an isostructural relationship of the synthesized compounds and only minor deviation from Vegard’s law. The optical band gap of these materials can be tuned in an energy range from 1.5 eV (RhCl3) to 1.2 eV (RhI3) by choosing the composition of the solid solution, while the samples also exhibit photoluminescence in similar energy ranges. Ultimately, the successful deposition of bulk as well as ultrathin 2D nanocrystals of RhBr x Cl3−x by CVT from 925 °C to 850 °C is shown, where the composition of the deposited crystals is precisely controlled by the choice of the starting composition and the initial amount of material. The high quality of the obtained nanocrystals is confirmed by atomic force microscopy, high resolution transmission electron microscopy and selected area electron diffraction. For RhBr x I3−x , the CVT from 900 °C to 825 °C is more difficult and has only been practically demonstrated for an exemplary case. According to the observed properties, these novel solid solutions and nanocrystals show a great potential for an application in optoelectronic devices.

Temperature-induced change in reactivity of the frequently used ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([C4 C1 im]BF4 ) is presented as a prerequisite for the rational screening of reaction courses in material synthesis. [C4 C1 im]BF4 becomes active with oxidic precursor compounds in reduction reaction at ϑ≥200 °C, even without the addition of an external reducing agent. The reaction mechanism of forming red amorphous selenium from SeO2 is investigated as a model system and can be described similarly to the Riley oxidation. The reactive species but-1-ene, which is formed during the decomposition of [C4 C1 im]BF4 , reacts with SeO2 and form but-3-en-2-one, water, and selenium. Elucidation of the mechanism was achieved by thermoanalytical investigations. The monotropic phase transition of selenium was analyzed by the differential scanning calorimetry. Beyond, the suitability of the single source oxide precursor Bi2 Se3 O9 for the synthesis of Bi2 Se3 particles was confirmed. Identification, characterization of formed solids succeeded by using light microscopy, XRD, SEM, and EDX.

Chemistry - a European journal 28(55), e202201281 (2022). doi:10.1002/chem.202201281, DUT-8(Ni) metal–organic framework (MOF) belongs to the family of flexible pillared layer materials. The desolvated framework can be obtained in the open pore form (op) or in the closed pore form (cp), depending on the crystal size regime. In the present work, we report on the behaviour of desolvated DUT-8(Ni) at elevated temperatures. For both, op and cp variants, heating causes a structural transition, leading to a new, crystalline compound, containing two interpenetrated networks. The state of the framework before transition (op vs. cp) influences the transition temperature: the small particles of the op phase transform at significantly lower temperature in comparison to the macroparticles of the cp phase, transforming close to the decomposition temperature. The new compound, confined closed pore phase (ccp), was characterized by powder X-ray diffraction and spectroscopic techniques, such as IR, EXAFS, and positron annihilation lifetime spectroscopy (PALS). Thermal effects of structural transitions were studied using differential scanning calorimetry (DSC), showing an overall exothermic effect of the process, involving bond breaking and reformation. Theoretical calculations reveal the energetics, driving the observed temperature induced phase transition., Published by Wiley-VCH, Weinheim

International audience; The tellurides of Bismuth and Antimony (Bi2Te3 and Sb2Te3) are prominent members of the V2VI3 material family that exhibit promising topological properties. We provide a method for the rational synthesis of mixed crystals of these mate-rials ((BixSb1−x)2Te3 with x = 0.1, …, 0.9) by means of a bottom-up CVT approach. Thermodynamic calculations showed the synthesis to be possible in the temperature range of 390 – 560°C without significant enrichment of either component and without adding a transport agent. The starting materials were synthesized and verified by XRD. Optimization exper-iments showed the ideal conditions for nanosheet synthesis to be T2 = 560°C, T1 = 390°C with a reaction time of t = 36 h. Crystals with heights of down to 12 nm (12 quintuple layers) were synthesized and analyzed by means of scanning elec-tron microscopy, energy-dispersive X-ray spectrometry and atomic force microscopy. High resolution transmission elec-tron microscopy confirmed the R3̄m crystal structure, high crystallinity and overall quality of the synthesized (BixSb1−x)2Te3 nanosheets. Magneto-transport measurements revealed that such ternary compounds can have a signifi-cantly reduced carrier density compared to the binary parent compounds.

Tungsten telluride WTe2 is the sole candidate of a group of two-dimensional layered transition metal dichalcogenides (TMDCs) MX2 with a thermodynamically stable 1T′-structure at room temperature. T...

Despite Chemical Vapor Transport (CVT) being a widely used method for crystal growth of inorganic substances, detailed mechanistic studies on the course of the crystallization process are rather se...

The transition metal halide α-titanium(III) chloride (α-TiCl3) is a layered two-dimensional compound and a well-established Ziegler–Natta catalyst for the polymerization of ethylene. A new synthesi...

Single crystals of the polytellurides RETe1.8 of gadolinium, terbium, and dysprosium were prepared by chemical vapor transport and alkali metal halide flux reactions. To determine proper synthesis conditions for the desired target composition, the binary phase diagram Gd-Te was evaluated by CalPhaD methods. The compounds are isostructural to SmTe1.8 and crystallize in space group P4/n (no. 85) with lattice parameters of a = 966.10(4), 960.00(3), and 957.33(2) pm and c = 1794.15(10), 1785.77(6), and 1779.38(5) pm for GdTe1.8, TbTe1.8 and DyTe1.8, respectively. The structures consist of puckered [RETe] double slabs and planar telluride layers composed of Te2 dumbbells and linear Te3 units in accordance with ELI-D based bonding analyses. The latter can be understood as a Te3(4–) anion. GdTe1.8 is a semiconductor with a bandgap of 0.19 eV/0.17 eV (experimental / calculated). Magnetization data confirm trivalent RE ions and indicate antiferromagnetic order at T(N) = 12 K for TbTe1.8 and T(N) = 9.8 K for DyTe1.8, whereas GdTe1.8 remains paramagnetic down to 2 K.

Ionic liquids are often considered as green alternatives of volatile organic solvents. The thermal behavior of the ionic liquids is relevant for a number of emerging large-scale applications at elevated temperature. Knowledge about the degradation products is indispensable for treatment and recycling of the used ionic liquids. The objective of this paper was an investigation of the short- and long-term stability of several 1-alkyl-3-methylimidazolium halides, determination of the degradation products, and the elucidation of their decomposition patterns and structure-stability relations. Short-term stability and mechanism of thermal degradation were investigated by a self-developed, innovative thermal analysis single-photon ionization time-of-flight mass spectrometry device with Skimmer coupling. The applied technology provides real-time monitoring of the forming species and allows tracing their change during the course of the decomposition. Therein, the almost fragment-free soft ionization with vacuum ultraviolet photons plays a crucial role. We have detected unfragmented molecules whose formation was only assumed by electron ionization. Nevertheless, the main decomposition products of the selected ionic liquids were alkyl imidazoles, alkenes, alkyl halides, and hydrogen halides. From the decomposition products, we have deduced the fragmentation patterns and discussed their interrelation with the length of the alkyl chain and the type of the halide anion. Our results did not suggest the evaporation of the investigated ionic liquids prior to their decomposition under atmospheric conditions. Long-term thermal stability and applicability were determined based on thermogravimetric analysis evaluated with a kinetic model. Thus, the time-dependent maximum operation temperature (MOT) for the respective ionic liquids has been calculated. As a rule, the short-term stability overestimates the long-term decomposition temperatures; the calculated MOT are significantly lower (at least 100 K) than the standardly obtained decomposition temperatures.

The 2D layered honeycomb magnet α-ruthenium(III) chloride (α-RuCl3) is a promising candidate to realize a Kitaev spin model. As alteration of physical properties on the nanoscale is additionally intended, new synthesis approaches to obtain phase pure α-RuCl3 nanocrystals have been audited. Thermodynamic simulations of occurring gas phase equilibria were performed and optimization of synthesis conditions was achieved based on calculation results. Crystal growth succeeded via chemical vapor transport (CVT) in a temperature gradient of 973 K to 773 K on YSZ substrates. Single crystal sheets of high crystallinity with heights ≤30 nm were obtained via pure CVT. The crystal properties were characterized by means of optical and electron microscopy, AFM, SAED, micro-Raman and XPS proving their composition, morphology, crystallinity and phase-purity. A highlight of our study is the successful individualization of nanocrystals and the delamination of nanosheets on YSZ substrates down to the monolayer limit (≤1 nm) which was realized by means of substrate exfoliation and ultrasonication in a very reproducible way.

The concept of maximum operation temperature is established for the prediction of the time dependent thermal stability of ionic liquids based on kinetic evaluation of thermogravimetric analysis. The influence of the furnace control parameters on the maximum operation temperature (MOT) is shown using the example of 1-methyl-3-propylimidazolium iodide ([C3C1im]I) with respect to three different parameter sets of a programmed proportional integral derivative (PID) controller of the TGA. Kinetics of thermal decomposition of [C3C1im]I have been investigated with the implementation of an improved kinetic model. The activation energy obtained using the Kissinger-Akahira-Sunose equation showed variations apparently due to the decomposition degree. The model compound is decomposed by a one-step kinetics, which results from pseudo zero order relationship of the activation energy to the conversion rate. The activation energy, pre-exponential factor, and the activation energy are strongly dependent on the parameters of TGA furnace controller.

Die Charakterisierung der Elemente nach ihrer Ordnungszahl und der Elektronenkonfiguration dient nicht nur der Einordnung in das Periodensystem. Die Beobachtung periodischer Eigenschaften der Elemente gibt uns auch einen Anhaltspunkt, dass die Art der chemischen Bindung zwischen Atomen durch die Anzahl der auseren Elektronen bestimmt ist. Mit der Elektronegativitat bekommen wir schlieslich eine sinnvolle Grose zur Abschatzung, ob ein Stoff in einer metallischen, ionischen oder kovalenten Bindung vorkommt.

Bislang stand der Austausch von Energie bei chemischen Reaktionen – vorrangig als Warmeenergie – im Vordergrund der Betrachtungen. Allerdings ist es unmoglich, Warme vollstandig in Arbeit zu transferieren. Die ubrige Warmemenge fuhrt zu irreversiblen Zustandsanderungen im System. Wir bezeichnen das Mas der irreversiblen Zustandsanderungen und damit das Aquivalent zur irreversiblen Warmemenge als Entropie. Ob ein Prozess freiwillig ablauft, hangt davon ab, ob abschliesend (nach Ausgleich von Enthalpie und Entropie) ein Energiegewinn oder -verlust eintritt. Dieser Energiebetrag ist die freie Enthalpie - der Zusammenhang wird durch die Gibbs-Helmholtz-Gleichung ausgedruckt.

In Molekulen ist die Elektronenverteilung nicht mehr kugelsymmetrisch, sondern in bestimmten Raumrichtungen entlang der Bindungselektronenpaare bevorzugt. Da die Molekule meistens kleine, in sich abgeschlossene Struktureinheiten darstellen, ist die Koordinationszahl dann nicht durch die Anordnung in einem dreidimensionalen Gitter eingeschrankt. In einer kovalenten Bindung konnen sich die Atome also relativ frei anordnen. Auf diese Weise sind bei Molekulen Koordinationszahlen von 2, 3, 4, 5, und 7 moglich. Eine systematische Beschreibung der Molekulstrukturen gelingt mithilfe des Modells der Valenzschalen-Elektronenpaar-Abstosung (VSEPR-Modell).

Atome bestehen aus Elementarteilchen: Die Zusammensetzung eines chemischen Elements aus Protonen, Neutronen und Elektronen bestimmt dessen Eigenschaften und die Stellung im Periodensystem. Die Anordnung der Elektronen in der Hulle eines Atoms erfolgt nicht auf festen Positionen, sondern innerhalb von Aufenthaltsraumen mit einer bestimmten Wahrscheinlichkeit. Eine anschauliche Vorstellung der Aufenthaltswahrscheinlichkeiten bekommt man durch die Atom-Orbitale. Die Stellung eines Elements im Periodensystem sowie die Geometrie und Orientierung der Orbitale des Elements im Raum haben fur die Beschreibung der Reaktivitat und der Art der chemischen Bindung eine grose Bedeutung.

Der Energieumsatz einer chemischen Reaktion fuhrt zur Anderung der Warmebilanz und des Ordnungszustandes des Systems. Zur quantitativen Beschreibung werden die Reaktionsgrosen der Enthalpie und der Entropie verwendet. Aus der Reaktionsenthalpie und der Reaktionsentropie kann man mithilfe der Gibbs-Helmholtz-Gleichung die freie Reaktionsenthalpie berechnen. Deren Wert ist unmittelbar mit der Gleichgewichtskonstante K fur die chemische Reaktion verknupft. Die zeitliche Abhangigkeit der Einstellung des chemischen Gleichgewichts wird durch die Reaktionsgeschwindigkeit beschrieben. Aus dem Geschwindigkeitsgesetz einer Reaktion lasst sich die Reaktionsordnung ablesen. Die Arrhenius-Gleichung beschreibt die Temperaturabhangigkeit der Reaktionsgeschwindigkeit.

Die Grenztypen der chemischen Bindung sind durch charakteristische Eigenschaften gekennzeichnet: Die ionische Bindung beruht auf den elektrostatischen Wechselwirkungen und damit auf ungerichteten Anziehungskraften zwischen positiv geladenen Kationen und negativ geladenen Anionen. Daraus resultieren uberwiegend Strukturen, die das Prinzip der dichtesten Kugelpackungen erfullen. Die metallische Bindung beruht in gleicher Weise auf elektrostatischen Wechselwirkungen der konstituierenden Teilchen. Die Strukturen der meisten Metalle konnen mit einem von drei einfachen Strukturtypen beschrieben werden. Das Bandermodell erklart anschaulich die Eigenschaften von Metallen und Halbleitern. Die Lokalisierung von Elektronen in der kovalenten Bindung fuhrt zur Bildung raumlich begrenzter Molekule, deren Struktur und Eigenschaften sehr gut mit Hilfe der VB-Theorie und der MO-Theorie beschrieben werden konnen.

The Ionic Liquid 1-butyl-3-methylimidazolium tetrafluoroborate [C4C1im]BF4 serves as a commonly solvent in inorganic material synthesis and analytics. Nevertheless, its application is frequently associated with trial and error approaches. Thereupon, detailed knowledge on the thermal behavior is the key information for understanding the reactivity of [C4C1im]BF4. 1-butyl-3-methylimidazolium tetrafluoroborate behaves as a glass in the cold, its glass transition temperature being ϑg = −83 °C. During heating with 10 K·min−1 [C4C1im]BF4 appears to be stable above 350 °C with onset temperatures ϑonset, DSC = 375 °C, ϑonset, DTG = 422 °C, and ϑonset, TG = 437 °C. Thereby, thermal decomposition occurs in a single step reaction forming 1-methyl-1H-imidazole (CH3C3H3N2 or C4H6N2), but-1-ene (C4H8), fluoromethane (CH3F) and boron trifluoride (BF3) as main species, as determined by thermogravimetry coupled with mass spectrometry and FTIR spectroscopy. To be more specific in thermal behavior, the temperature and time dependent stability is evaluated here on the basis of the kinetic model of maximum operation temperature − MOT. Clearly, thermal stability rises with application time, thus being 193 °C for one hour, while reaching only 141 °C for one day, and 114 °C for one week. The incipient decomposition (≤ 1 %) at the calculated time dependent maximum operation temperature finally is verified by optical analysis, infrared (IR), and nuclear magnetic resonance (NMR) spectroscopy.

Phase pure polycrystalline PbP7 was prepared from the elements via a lead flux. Crystalline pieces with edge-lengths up to 1 mm were obtained. The assignment of the previously published P-31 solid state NMR spectrum to the seven distinct crystallographic sites was accomplished by radio-frequency driven dipolar recoupling (RFDR) experiments. As commonly found in other solid polyphosphides there is no obvious correlation between the P-31 chemical shift and structural parameters. PbP7 decomposes incongruently under release of phosphorus forming liquid lead as remainder. The thermal decomposition starts at T > 550 K with a vapor pressure almost similar to that of red phosphorus. Electronic structure calculations reveal PbP7 as a semiconductor according to the Zintl description and clearly shows the stereo active Pb-6s(2) lone pairs in the electron localization function ELF. (C) 2015 ELSEVIER. All rights reserved.

Germanium (Ge) nanowires (NWs) were grown in-plane on nano-structured Si(001)/SiO2 substrates by molecular beam epitaxy using gold (Au) as solvent. The site-selective NW growth was enabled by a rectangular array of gold droplets on silicon (Si) tips with a Au nuclei density below 0.25 µm-2 on the surrounding silicon oxide (SiO2). The initial growth of Ge NWs starting from Si-Au droplets with SixGe1-x nucleation from ternary alloy is discussed from a thermodynamic point of view. The in-plane NW elongation occurred within 〈110〉 directions on the substrate and NWs were mainly bounded by two 55° inclined {111} facets and a less pronounced planar (001) top facet. Fully relaxed crystal lattices of Ge NWs were observed from two-dimensional reciprocal space maps of X-ray diffraction measurements.

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.

Phase formation, stability, crystal and electronic structures of IrPTe are investigated from experiment and quantum chemical calculations. The phase formation is studied from thermodynamic data and CalPhaD modeling. Applying a high-temperature gas-balance a formation pathway for IrPTe is studied from the elements and the binary parent compounds IrTe2 and IrP2. The obtained paracostibite (CoSbS) type structure contains rarely occurring heteroatomic P–Te dumbbells. The stability of IrPTe and the found structure is studied from DFT calculations with respect to the elements, IrTe2 and IrP2, and possible polymorphs. Probable metastable modifications with XY dumbbells (as known for isoelectronic compounds like CoAsS) are obtained from systematic DFT modelling. Phase transitions are predicted form the equation of states (EOS). According to its electronic band structure IrPTe is predicted as small gap (ΔEg = 0.5 eV) semiconductor.

The thermochemical behavior of 1-ethyl-3-methylimidazolium [EMIm] halides (Cl, Br and I) has been investigated for their crystalline and liquid states in the temperature range from −90 °C to 600 °C using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The temperatures and enthalpies of phase transitions have been determined: Tfus = 86(1) °C, ΔHfus = 14.2(0.7) kJ mol−1 ([EMIm]Cl); Tfus = 67(1) °C, ΔHfus = 19.3(0.7) kJ mol−1 ([EMIm]Br); and Tfus = 74(1) °C, ΔHfus = 16.9(0.6) kJ mol−1 ([EMIm]I). The decomposition temperatures, determined by onset of DTG at 1 K min−1 are 233(5) °C ([EMIm]Cl), 246(5) °C ([EMIm]Br), and 249(5) °C ([EMIm]I). The maximum operation temperature (MOT) has been estimated based on dynamic TGA for an operation time of 24 h: 132 °C ([EMIm]Cl), 149 °C ([EMIm]Br), 139 °C ([EMIm]I) and 8000 h: 76 °C ([EMIm]Cl), 90 °C ([EMIm]Br), 77 °C ([EMIm]I). The decomposition products of the investigated ionic liquids (ILs) after heating experiments were identified by means of TGA complemented with mass spectrometry (MS), for establishment of the mechanism of thermal decomposition of the ILs. Complete degradation of [EMIm]X ionic liquids occurs under formation of characteristic molecule fragments CH3+, NH+, and X+, CH3X+, C2H5X+ (X = Cl, Br, I).

The synthesis of the phosphide telluride Zr2+xPTe2 was accomplished by a solid-state reaction from the elements. Le Bail refinements of the data from the as-synthesized crystalline powders as well as the thermal decomposition of Zr2PTe2 along the homogeneity range Zr2+xPTe2 with the release of P4(g) and Te2(g) evidence a maximum zirconium content corresponding to the composition Zr2.5PTe2. The thermal decomposition product of Zr2.5PTe2 undergoes a phase transformation to “Zr2PTe”, which adopts the structural motif of the binary phases ZrTe and ZrTe2. The new phase “Zr2PTe” has a wide homogeneity range Zr2–xP1–yTe1+y and tolerates a deficit in the cation position and a mixed occupation of the anions. The composition of the crystalline decomposition product was determined to be Zr1.95P0.84Te1.16 by Rietveld refinement and by analysis of the elemental composition by inductively coupled plasma optical emission spectroscopy (ICP-OES). Zr1.95P0.84Te1.16 crystallizes in the hexagonal space group P63/mmc (no. 194) with lattice constants a = 3.8726(1) A and c = 13.008(1) A.