@misc{PielnhoferBachhuberSchmidtetal., author = {Pielnhofer, Florian and Bachhuber, Frederik and Schmidt, Peer and Nilges, Tom and Weihrich, Richard}, title = {Mit DFT-Modellierungen zu neuen Polyanionenverbindungen}, series = {Zeitschrift f{\"u}r Anorganische und Allgemeine Chemie}, volume = {638}, journal = {Zeitschrift f{\"u}r Anorganische und Allgemeine Chemie}, number = {10}, doi = {10.1002/zaac.201204137}, pages = {S. 1634}, abstract = {Verbindungen mit ionischen Baueinheiten erweisen sich als geeignete Materialien zur Energie- und Ressourcennutzung. Beispiele sind Li-Elektrodenmaterialien oder neue Thermoelektrika, die aufgrund ihrer Teilstrukturen schaltbar werden. Das Design neuer funktionaler Materialien verlangt dabei nach einem grundlegenden Verst{\"a}ndnis von Struktur-Eigenschafts-Beziehungen, metastabilen Strukturen und Umwandlungen. Dies bedarf des Einsatzes kombinierter experimenteller und theoretischer Methoden. Zur systematischen Erforschung metastabiler Strukturen wurde j{\"u}ngst das Konzept der Strukturvorhersage in Energielandschaften mit ab initio Methoden auf das System P1-xAsx angewandt und mit experimentellen Messungen verkn{\"u}pft. Im n{\"a}chsten Schritt wurden Verbindungen mit ionischen Teilstrukturen des As, Sb, Se und Te untersucht. Modellhaft wurden nun Zintl-Systemen wie IrPTe und PtSnTe neue m{\"o}gliche metastabile Strukturen identifiziert und auf Funktionalisierungen untersucht.}, language = {de} } @misc{PoddigDonathGebaueretal., author = {Poddig, Hagen and Donath, Tom and Gebauer, Paul and Finzel, Kati and Kohout, Miroslav and Wu, Yuandong and Schmidt, Peer and Doert, Thomas}, title = {Rare Earth Metal Polytellurides RETe1.8 (RE = Gd, Tb, Dy) - Directed Synthesis, Crystal and Electronic Structures, and Bonding Features}, series = {Zeitschrift f{\"u}r Anorganische und Allgemeine Chemie}, volume = {644}, journal = {Zeitschrift f{\"u}r Anorganische und Allgemeine Chemie}, number = {24}, issn = {1521-3749}, doi = {10.1002/zaac.201800382}, pages = {1886 -- 1896}, abstract = {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.}, language = {en} } @misc{ScholzSchoeneichSchmidt, author = {Scholz, Tanja and Sch{\"o}neich, Michael and Schmidt, Peer}, title = {Understanding Solid-State Phase-Formation Processes by Usingthe High-Temperature Gas Balance: The Example of Zr₂PTe₂}, series = {European Journal of Inorganic Chemistry}, journal = {European Journal of Inorganic Chemistry}, number = {21}, doi = {10.1002/ejic.201900281}, pages = {2577 -- 2582}, abstract = {Inorganic solid-state synthesis with phosphorus and tellurium requires a careful control of the reaction parameters because of the high volatility of the components. This initial disadvantage can be used as a benefit for the investigation of phase formation mechanisms by analyzing the individual vapor pressure behavior. The high-temperature gas-balance is introduced as a device for detection of heterogeneous solid-gas equilibria in closed reaction systems. The experimentally challenging synthesis of the phosphide telluride Zr₂PTe₂ is examined as a model system: optimized synthesis runs at lower temperatures (ϑ = 650 °C) in a faster time, while the quantity as well as the crystalline powder quality is increased. A stepwise solid-solid reaction of zirconium and tellurium according to Ostwald's rule of stages and the shrinking core model is revealed while phosphorus sublimes and subsequently condenses to react to the ternary compound. Additional phenomena such as melting, expansion, and mechanical instabilities can be observed that broaden the possibilities of the gas- balance.}, language = {en} } @misc{HansenWelsFroeschkeetal., author = {Hansen, Felix and Wels, Martin and Froeschke, Samuel and Popov, Alexey and Wolf, Daniel and B{\"u}chner, Bernd and Schmidt, Peer and Hampel, Silke}, title = {Thermodynamic Evaluation and Chemical Vapor Transport of Few-Layer WTe2}, series = {Crystal Growth and Design}, volume = {20}, journal = {Crystal Growth and Design}, number = {11}, issn = {1528-7505}, doi = {10.1021/acs.cgd.0c01004}, pages = {7341 -- 7349}, abstract = {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. The binary system W/Te was audited with respect to a rational approach of planning and realization of a bottom-up synthesis of WTe2 nanostructures. Thus, the parameters of the synthesis via chemical vapor transports (CVT) were derived by thermodynamic simulations of the reaction pathway according to the Calphad method. Reflecting on the peritectic melting behavior at 1020 °C, the values of ΔfHm° (298 K) = -26.5 kJ·mol-1 and Sm° (298 K) = 132 J·mol-1 ·K-1 have been obtained. According to modeling, crystal growth by short time vapor transport is reasonable under the addition of bromine or TeBr4 in the temperature range between 650 and 750 °C. Experimental implementation of crystal growth of WTe2 nanosheets succeeded in a temperature gradient from 725 to 675 °C on yttria-stabilized zirconia (YSZ) (111) substrates, observing the deposition of single crystal sheets of high crystallinity with thicknesses of 15-20 nm (∼20-30 layers). The high crystallinity, pristine morphology, and overall quality of the deposited nanosheets is shown by means of atomic resolution transmission electron microscopy, selected area electron diffraction (SAED), and atomic force microscopy as well as profound double-polarized Raman spectroscopy.}, language = {en} } @misc{KnorrSchmidt, author = {Knorr, Monika and Schmidt, Peer}, title = {Reactivity of ionic liquids: Reductive effect of [C4C1im]BF4 to form particles of red amorphous selenium and Bi2Se3 from oxide precursors}, series = {ChemistryOpen}, volume = {10}, journal = {ChemistryOpen}, number = {2}, issn = {2191-1363}, doi = {10.1002/open.202000264}, pages = {125 -- 140}, abstract = {Temperature-induced change in reactivity of the frequently used ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([C4C1im]BF4) is presented as a prerequisite for the rational screening of reaction courses in material synthesis. [C4C1im]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 [C4C1im]BF4, reacts with SeO2 and form but-3-en-2-one, water, and selenium. Elucidation of the mechanism was achieved by thermoanalytical investigations. The mono-tropic phase transition of selenium was analyzed by the differential scanning calorimetry. Beyond, the suitability of the single source oxide precursor Bi2Se3O9 for the synthesis of Bi2Se3 particles was confirmed. Identification, characterization of formed solids succeeded by using light microscopy, XRD, SEM, and EDX.}, language = {en} } @misc{HansenFuckeCharvinetal., author = {Hansen, Felix and Fucke, Rico and Charvin, Titouan and Froeschke, Samuel and Wolf, Daniel and Giraud, Romain and Dufouleur, Joseph and Gr{\"a}ßler, Nico and B{\"u}chner, Bernd and Schmidt, Peer and Hampel, Silke}, title = {Direct Deposition of (BixSb1-x)2Te3 Nanosheets on Si/SiO2 Substrates by Chemical Vapor Transport}, series = {Crystal growth \& design}, volume = {22}, journal = {Crystal growth \& design}, number = {4}, issn = {1528-7505}, doi = {10.1021/acs.cgd.1c01446}, pages = {2354 -- 2363}, abstract = {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 materials ((BixSb1-x)2Te3 with x = 0.1, ..., 0.9) by means of a bottom-up chemical vapor transport (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 X-ray diffraction (XRD). Optimization experiments 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 electron microscopy, energy-dispersive X-ray spectrometry, and atomic force microscopy. High-resolution transmission electron microscopy confirmed the R3̅m crystal structure, high crystallinity, and overall quality of the synthesized (BixSb1-x)2Te3 nanosheets. Magnetotransport measurements revealed that such ternary compounds can have a significantly reduced carrier density compared to the binary parent compounds.}, language = {en} } @misc{PutzeRitschelChekhoninetal., author = {Putze, Philipp and Ritschel, Tobias and Chekhonin, Paul and Geck, Jochen and Wolf, Daniel and Popov, Alexey and B{\"u}chner, Bernd and Schmidt, Peer and Hampel, Silke}, title = {Creating chirality in WSe₂ through screw dislocations by chemical vapor transport}, series = {Nanoscale horizons}, volume = {10}, journal = {Nanoscale horizons}, number = {5}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, doi = {10.1039/D4NH00567H}, pages = {944 -- 956}, abstract = {Screw dislocation-driven nanostructures of two-dimensional transition metal dichalcogenides (2D TMDs) can feature chirality that enables prominent asymmetric optical properties. One of the outstanding representatives is WSe₂ as it can exhibit intriguing new size and shape-dependent chemical and physical properties compared to its bulk counterpart. Crystal growth control in nanostructures with screw dislocation-driven growth is central for exploiting their structure-related properties. However, bottom-up syntheses of 2D TMDs usually contain 'trial and error' approaches. Here we report on the rational synthesis planning and realizing for the binary system W:Se to achieve chirality in nano-scale crystals by chemical vapor transport (CVT). For that purpose, key parameters were modelled based on thermodynamic datasets. Thus, crystal growth by CVT under addition of SeCl4 succeeds for right-handed spiral nanocrystals from 850 °C to 800 °C with a dwell time of 60 min, while left-handed spirals are obtained from 915 °C to 860 °C. Surface-fused SiO₂ nanoparticles on an Si(100) substrate served as potential nucleation points. Chirality of screwed WSe₂ was unprecedentedly investigated by circular-polarized Raman Spectroscopy and showed an intensity increase of the E¹₂g mode of 29\% and 15\% for right and left-handed spirals, respectively. Pyramid-like WSe2 analyzed by atomic force microscopy exhibits step heights of around 10 nm. Electron backscatter diffraction patterns reveal a convex curvature for WSe₂ with the curvature radii determined as Rx = (270 ± 32) μm and Ry = (141 ± 9) μm, respectively.}, language = {en} } @misc{PutzeWolfChekhoninetal., author = {Putze, Philipp and Wolf, Daniel and Chekhonin, Paul and Popov, Alexey and Ritschel, Tobias and Lubk, Axel and Geck, Jochen and B{\"u}chner, Bernd and Schmidt, Peer and Hampel, Silke}, title = {Twisted and screw dislocation-driven growth of MoSe₂ nanostructures by chemical vapor transport}, series = {Nano research}, journal = {Nano research}, number = {18}, publisher = {Tsinghua University Press}, issn = {1998-0000}, doi = {10.26599/NR.2025.94908020}, pages = {1 -- 23}, abstract = {Twisted multilayers of two-dimensional materials attract widespread research interest due to their intriguing electronic and optical properties related to their chiral symmetry breaking and Moir{\´e} effects. The two-dimensional transition metal dichalcogenide MoSe₂ is a particular promising material for twisted multilayers, capable of sustaining Moir{\´e} excitons. Here, we report on a rational bottom-up synthesis approach for twisted MoSe₂ flakes by chemical vapor transport (CVT). Screw dislocation-driven growth was forced by surface-fused SiO₂ nanoparticles on the substrates that serve as potential nucleation points in low supersaturation condition. Thus, crystal growth by in-situ CVT under addition of MoCl₅ leads to bulk 2H-MoSe₂ in a temperature gradient from 900 °C to 820 °C with a dwell time of 96 h. Hexagonally shaped 2H-MoSe₂ flakes were grown from 710 °C to 685 °C with a dwell time of 30 min on SiO₂@Al₂O₃(0001) substrates. Electron backscatter diffraction as well as electron microscopy reveals the screw dislocation-driven growth of triangular 3R-MoSe₂ with individual step heights between 0.9 nm and 2.9 nm on SiO₂@Si(100) under the same conditions. Finally, twisted MoSe₂ flakes exhibiting a twist angle of 19° with respect to the [010] zone axis could be synthesized.}, language = {en} }