@techreport{SchmidtEfimova, author = {Schmidt, Peer and Efimova, Anastasia}, title = {Kristallisationsverhalten von Phasenwechselmaterialien als Latentw{\"a}rmespeicher (KristallLaW): Abschlussbericht}, publisher = {BTU Cottbus - Senftenberg, Fachgebiet Anorganische Chemie}, address = {Senftenberg}, doi = {10.2314/GBV:884496287}, pages = {44}, abstract = {Phasenwechselmaterialien (PCM) sind chemische Verbindungen oder deren Mischungen, die bei einer definierten Temperatur schmelzen bzw. erstarren. Der zyklische Einsatz von W{\"a}rmespeichern erm{\"o}glicht den Ausgleich von {\"U}berlasten f{\"u}r den Bedarf oder den „Abfall" von W{\"a}rme sowie die Vergleichm{\"a}ßigung von W{\"a}rmeprofilen. Bestehende anorganische Materialien weisen {\"u}berwiegend Einschr{\"a}nkungen bez{\"u}glich der Anforderungen an eine geringe Hysterese von Aufheizung und Abk{\"u}hlung auf. Das Maß der Unterk{\"u}hlung der Schmelze sowie ein zyklenstabiler W{\"a}rmeaustausch kann aber durch Zus{\"a}tze als Kristallisationshilfen (Keimbildner) gesteuert werden. Im vorliegenden Bericht werden die Keimbildung und Kristallisation von Phasenwechselmaterialien unter folgenden Gesichtspunkten diskutiert: Methoden der Thermischen Analyse zur Untersuchung der thermochemischen Eigenschaften von PCM, thermochemische Eigenschaften anorganischer Salze und Salzhydrate als PCM, dominierende Kristallstrukturen und Strukturmotive anorganischer Salze und Salzhydrate als PCM, dominierende Kristallstrukturen und Strukturmotive anorganischer Stoffe als homogener und heterogener Keimbildner, {\"A}nderung der thermochemischen Eigenschaften von PCM bei Zusatz von Keimbildnern, geeignete Konzentrationsbereiche von Keimbildnern, Homogenit{\"a}t/Segregation von Phasen.}, language = {de} } @book{BinnewiesFinzeRadiusetal., author = {Binnewies, Michael and Finze, Maik and Radius, Udo and Schmidt, Peer}, title = {Anorganische Chemie, Band 6: Nebengruppen - Teil 1}, edition = {1. Auflage}, publisher = {Springer}, address = {Heidelberg}, isbn = {978-3-662-55904-8}, pages = {61}, abstract = {Stellung der Nebengruppenelemente im Periodensystem, Gruppeneigenschaften, Gewinnung der Metalle, die Nebengruppen (Gruppen 3 bis 12)}, language = {de} } @book{BinnewiesFinzeRadiusetal., author = {Binnewies, Michael and Finze, Maik and Radius, Udo and Schmidt, Peer}, title = {Anorganische Chemie, Band 7: Nebengruppen - Teil 2}, edition = {1. Auflage}, publisher = {Springer}, address = {Heidelberg}, isbn = {978-3-662-55906-2}, pages = {64}, abstract = {Koordinationschemie,Konzepte der chemischen Bindung in Komplexverbindungen}, language = {de} } @book{BinnewiesFinzeRadiusetal., author = {Binnewies, Michael and Finze, Maik and Radius, Udo and Schmidt, Peer}, title = {Anorganische Chemie, Band 8: Metallorganische Chemie der {\"U}bergangsmetalle}, edition = {1. Auflage}, publisher = {Springer}, address = {Heidelberg}, isbn = {978-3-662-56030-3}, pages = {87}, language = {de} } @book{BinnewiesFinzeRadiusetal., author = {Binnewies, Michael and Finze, Maik and Radius, Udo and Schmidt, Peer}, title = {Anorganische Chemie, Band 9: Festk{\"o}rperchemie}, edition = {1. Auflage}, publisher = {Springer}, address = {Heidelberg}, isbn = {978-3-662-47577-5}, pages = {91}, abstract = {Beschreibung kristalliner Strukturen, Strukturen anorganischer Festk{\"o}rper und Methoden zur Synthese und Kristallz{\"u}chtung}, language = {de} } @book{BinnewiesFinzeRadiusetal., author = {Binnewies, Michael and Finze, Maik and Radius, Udo and Schmidt, Peer}, title = {Anorganische Chemie, Band 10: Lanthanoide}, edition = {1. Auflage}, publisher = {Springer}, address = {Heidelberg}, isbn = {978-3-662-47543-0}, pages = {28}, abstract = {Vorkommen, Gewinnung und Verbindungen der Lanthanoide - Anwendungen der Lanthanoide und ihrer Verbindungen}, language = {de} } @misc{EfimovaVargaMatuscheketal., author = {Efimova, Anastasia and Varga, Janos and Matuschek, Georg and Saraji-Bozorgzad, Mohammad R. and Denner, Thomas and Zimmermann, Ralf and Schmidt, Peer}, title = {Thermal Resilience of Imidazolium-Based Ionic Liquids—Studies on Short- and Long-Term Thermal Stability and Decomposition Mechanism of 1-Alkyl-3-methylimidazolium Halides by Thermal Analysis and Single-Photon Ionization Time-of-Flight Mass Spectrometry}, series = {Journal of Physical Chemistry B}, volume = {122}, journal = {Journal of Physical Chemistry B}, number = {37}, doi = {10.1021/acs.jpcb.8b06416}, pages = {8738 -- 8749}, abstract = {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.}, language = {en} } @incollection{NilgesSchmidtWeihrich, author = {Nilges, Tom and Schmidt, Peer and Weihrich, Richard}, title = {Phosphorus: The Allotropes, Stability, Synthesis, and Selected Applications}, series = {Encyclopedia of Inorganic and Bioinorganic Chemistry}, booktitle = {Encyclopedia of Inorganic and Bioinorganic Chemistry}, editor = {Scott, Robert A.}, edition = {2. Auflage}, publisher = {John Wiley Sons}, address = {Hoboken, US}, isbn = {978-1-119-95143-8}, doi = {10.1002/9781119951438.eibc2643}, pages = {1 -- 19}, abstract = {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.}, language = {en} } @misc{GroenkeSchmidtValldoretal., author = {Gr{\"o}nke, Martin and Schmidt, Peer and Valldor, Martin and Oswald, Steffen and Wolf, Daniel and Lubk, Axel and B{\"u}chner, Bernd and Hampel, Silke}, title = {Chemical vapor growth and delamination of α-RuCl3 nanosheets down to the monolayer limit}, series = {Nanoscale}, volume = {10}, journal = {Nanoscale}, number = {40}, issn = {2040-3372}, doi = {10.1039/C8NR04667K}, pages = {19014 -- 19022}, abstract = {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.}, language = {en} } @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} } @inproceedings{BeckmannGuentherSchmidtetal., author = {Beckmann, Jens and G{\"u}nther, David and Schmidt, Peer and Sch{\"o}neich, Michael and Klepel, Olaf}, title = {Template assisted synthesis of porous carbon materials using porous concrete as a template}, series = {5th International Sypmosium on "Carbon on Catalysis", Books of abstracts, Bressanone/Brixen, 2012}, booktitle = {5th International Sypmosium on "Carbon on Catalysis", Books of abstracts, Bressanone/Brixen, 2012}, pages = {S. 94}, language = {en} } @inproceedings{BeckmannGuentherKlepeletal., author = {Beckmann, Jens and G{\"u}nther, David and Klepel, Olaf and Schmidt, Peer}, title = {Porous concrete as a template for the synthesis of porous carbon materials}, series = {Annual World Conference on Carbon : (Carbon 2012) Krakow, Poland 17-22 June 2012}, booktitle = {Annual World Conference on Carbon : (Carbon 2012) Krakow, Poland 17-22 June 2012}, publisher = {Curran}, address = {Red Hook, NY}, isbn = {978-1-62993-436-5}, pages = {854}, 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{GroenkePohfleppSchmidtetal., author = {Gr{\"o}nke, Martin and Pohflepp, Danny and Schmidt, Peer and Valldor, Martin and Oswald, Steffen and Wolf, Daniel and Hao, Qi and Steiner, Udo and B{\"u}chner, Bernd and Hampel, Silke}, title = {Simulation and synthesis of alpha-MoCl₃ nanosheets on substrates by short time chemical vapor transport}, series = {Nano-Structures \& Nano-Objects}, journal = {Nano-Structures \& Nano-Objects}, number = {19}, issn = {2352-507X}, doi = {10.1016/j.nanoso.2019.100324}, pages = {1 -- 7}, abstract = {Alpha-molybdenum(III) chloride (MoCl₃) belongs to layered van-der-Waals materials, which are in focus to exhibit interesting properties due to their weak chemical and magnetic interactions. Especially the structure of alpha-MoCl₃ has been discussed in terms of symmetry breaking dimerization of Mo atoms at room temperature, which might led to exotic ground states. By exploiting the 2D materials characteristics, an investigation of physical properties on the nanoscale is intended. We herein demonstrate the probably first approach to synthesize phase pure, as-grown alpha-MoCl₃ few-layer nanosheets by means of a pure short time chemical vapor transport (CVT) process. Vapor growth benefits from a one-step deposition of high crystalline alpha-MoCl₃ nanosheets without stacking faults on a substrate. Thus, mostly applied subsequent delamination, associated with the introduction of structural defects, becomes redundant. According to the CVT process thermodynamic simulations of gas phase equilibria have been performed and the synthesis conditions could be optimized based on the calculation results. By CVT the as-grown nanolayers are deposited on sapphire (Al₂O₃) substrates by applying a temperature gradient of 70 K from 743 K to 673 K. Single crystalline sheets with thicknesses ≤75 nm down to five layer (3 nm) could be obtained by using a pure CVT process. According to the deposited nanostructures we approve the desired composition, morphology, phase purity and high crystallinity by using several microscopy and spectroscopy techniques. Furthermore, we show micro-RAMAN measurements which hint at a slight increase in phonon energies for nanosheets in comparison to the corresponding bulk phase.}, language = {en} } @misc{GroenkeArroziBronkallaetal., author = {Gr{\"o}nke, Martin and Arrozi, Ubed S. F. and Bronkalla, Nadine and Schmidt, Peer and Valldor, Martin and Oswald, Steffen and Woodcock, Thomas G. and Eckert, Victoria and Hao, Qi and Pl{\"u}schke, Laura and Lederer, Albena and Nielsch, Kornelius and B{\"u}chner, Bernd and Kaskel, Stefan and Hampel, Silke}, title = {Layered α-TiCl₃: Microsheets on YSZ Substrates for Ethylene Polymerization with Enhanced Activity}, series = {Chemistry of Materials}, volume = {31}, journal = {Chemistry of Materials}, number = {14}, doi = {10.1021/acs.chemmater.9b01818}, pages = {5305 -- 5313}, abstract = {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 synthesis technique is used to obtain thin sheets of α-TiCl₃ that show exceptional physical properties in contrast to their bulk counterparts, due to an enlarged surface-to-volume ratio. Chemical vapor transport (CVT) of α-titanium(III) chloride directly on substrates results in microsheets that exhibit an improved catalytic effect. For rational planning of synthesis conditions, thermodynamic simulations of occurring gas-phase equilibria were performed. Based on these calculation results, crystal growth was achieved by adding GaCl₃via pure short term CVT in a temperature gradient of 700-600 K on yttrium-stabilized zirconia (YSZ) substrates. Phase pure, as-grown, single crystal sheets with high crystallinity and a thickness of around 4 μm were obtained. These thin sheets of α-TiCl₃ on YSZ substrates were implemented as catalysts for the ethylene polymerization reaction. A significant improvement of catalytic activity of 16\% was achieved, probably due to an increased surface-to-volume ratio. As a highlight, the as-grown microsheets were exfoliated subsequently to a thickness lower than 200 nm and an even higher catalytic activity of up to 24\% was confirmed experimentally due to delamination effects. This is the first time that an improved catalytic effect of α-TiCl₃ is observed as a result of downscaling from bulk to microsheets by CVT.}, language = {en} } @book{Schmidt, author = {Schmidt, Peer}, title = {Allgemeine Chemie}, edition = {1. Auflage}, publisher = {Springer-Spektrum}, address = {Heidelberg}, isbn = {978-3-662-57846-9}, pages = {268}, abstract = {Atombau, Konzepte der Chemischen Bindung sowie Thermodynamische Kenngr{\"o}ßen zu Beschreibung chemischer Gleichgewichte und zeitabh{\"a}ngige Einstellung des chemischen Gleichgewichts}, language = {de} } @misc{GroenkeBuschbeckSchmidtetal., author = {Gr{\"o}nke, Martin and Buschbeck, Benjamin and Schmidt, Peer and Valldor, Martin and Oswald, Steffen and Hao, Qi and Lubk, Axel and Wolf, Daniel and Steiner, Udo and B{\"u}chner, Bernd and Hampel, Silke}, title = {Chromium Trihalides CrX₃(X = Cl, Br, I): Direct Deposition of Micro- and Nanosheets on Substrates by Chemical Vapor Transport}, series = {Advanced Materials Interfaces}, volume = {6}, journal = {Advanced Materials Interfaces}, number = {24}, issn = {2196-7350}, doi = {10.1002/admi.201901410}, pages = {11}, abstract = {The experimental observation of intrinsic ferromagnetism in single layered chromium trihalides CrX₃ (X = Cl, Br, I) has gained outstanding attention recently due to their possible implementation in spintronic devices. However, the reproducible preparation of highly crystalline chromium(III) halide nanolayers without stacking faults is still an experimental challenge. As chromium trihalides consist of adjacent layers with weak interlayer coupling, the preparation of ultrathin CrX₃ nanosheets directly on substrates via vapor transport proves as an advantageous synthesis technique. It is demonstrated that vapor growth of ultrathin highly crystalline CrX₃ micro- and nanosheets succeeds directly on yttrium stabilized zirconia substrates in a one-step process via chemical vapor transport (CVT) in temperature gradients of 100 K (600°C → 500°C for CrCl₃ and 650°C → 550°C for CrBr₃ or CrI₃) without a need for subsequent delamination. Due to simulation results, optimization of synthesis conditions is realized and phase pure CrX₃ nanosheets with thicknesses ≤25 nm are obtained via short term CVT. The nanosheets morphology, crystallinity, and phase purity are analyzed by several techniques, including microscopy, diffraction, and spectroscopy. Furthermore, a potential subsequent delamination technique is demonstrated to give fast access to CrX₃ monolayers using the example of CrCl₃ .}, language = {en} } @misc{PabstChangFinzeletal., author = {Pabst, Falk and Chang, Jen-Hui and Finzel, Kati and Kohout, Miroslav and Schmidt, Peer and Ruck, Michael}, title = {The Subbromide Bi5Br4 - On the Existence of a Hidden Phase}, series = {Zeitschrift f{\"u}r Anorganische und Allgemeine Chemie}, volume = {646}, journal = {Zeitschrift f{\"u}r Anorganische und Allgemeine Chemie}, number = {3}, doi = {10.1002/zaac.201800149}, pages = {149 -- 155}, abstract = {Black and irregularly shaped crystals of the bismuth-rich bromide Bi5Br4 were obtained as a by-product of the reaction of CsBr, Bi, and BiBr3. X-ray diffraction on a single-crystal revealed its orthorhombic structure with the space group Pmmn (no. 59) and lattice parameters a = 1800.0(2) pm, b = 1476.1(1) pm, and c = 924.5(2) pm at 296 K. The structure is composed of Bi82+ and Bi95+ polycations and bromidobismuthate(III) anions according to the structured formula Bi5Br4 = Bi20Br16 = Bi82+Bi95+[BiBr5]2-[Bi2Br11]5-. Bi5Br4 is the bismuth-richest among the bismuth subhalides containing isolated polycations. Extensive differential scanning calorimetry studies indicate that Bi5Br4 decomposes at 262 °C, i.e. one degree below the bismuth-rich eutectic at 263 °C. All attempts towards a rational synthesis yielded predominantly the neighboring phases BiBr and Bi6Br7.}, language = {en} } @misc{LangeErnstTeubneretal., author = {Lange, Felix and Ernst, Owen C. and Teubner, Thomas and Richter, Carsten and Schmidbauer, Martin and Skibitzki, Oliver and Schroeder, Thomas and Schmidt, Peer and Boeck, Torsten}, title = {In-plane growth of germanium nanowires on nanostructured Si(001)/SiO2 substrates}, series = {Nano Futures}, volume = {4}, journal = {Nano Futures}, number = {3}, issn = {2399-1984}, doi = {10.1088/2399-1984/ab82a0}, pages = {1 -- 8}, abstract = {Germanium (Ge) nanowires (NWs) were grown in-plane on nano-structured Si(001)/SiO2 substrates by molecular beam epitaxy using gold (Au) as the solvent. The site-selective NW growth was enabled by a rectangular array of gold droplets on silicon (Si) tips with an 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.}, language = {en} } @misc{HeinemannSchmidt, author = {Heinemann, Robert and Schmidt, Peer}, title = {Crystal Growth by Chemical Vapor Transport: Process Screening by Complementary Modeling and Experiment}, series = {Crystal Growth \& Design}, volume = {20}, journal = {Crystal Growth \& Design}, number = {9}, issn = {1528-7505}, doi = {10.1021/acs.cgd.0c00679}, pages = {5986 -- 6000}, abstract = {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 few. In this study, an elaborated experimental screening run combined with sophisticated modeling of the respective heterogeneous equilibria is presented: Crystal growth of germanium by vapor transport with the addition of iodine has been chosen as a model system for validation of the applied method spectrum. In order to record the course and the interplay of heterogeneous equilibrium and non-equilibrium reactions in the system Ge-I, the experimental setup of high-temperature gas-balance (HTGB) is applied. Additionally, the observed evaporation processes are compared with saturation curves of corresponding volatile substances and, thus, can be assigned to individual species within the system. In this experimental screening, a phase sequence means to examine how the condensed phases undergo iodine depletion and how the gaseous phase undergoes a germanium enrichment when the temperature is increased. This phase screening combined with annealing experiments in the course of the phase sequence helps to analyze stepwise non-equilibrium products and to identify the characteristic species. Subsequently, for the evaluation of the composition of the gaseous phase, and for the deduction of the vapor transport mechanism, thermodynamic modeling by the CalPhaD method is performed. For the reference system, it is confirmed that iodine does not act as the transport agent. Instead, GeI4 is responsible for the volatilization of germanium, forming GeI2. Nevertheless, investigations clearly illustrate how GeI4 forms naturally in the phase sequence in the system Ge-I, which makes direct addition of it unnecessary. The recommended temperature range for vapor transport of germanium spans from 460 to 800 °C. Modeling shows that migration rates for germanium reaches a maximum at a mean temperature between 540 and 550 °C. Finally, vapor transport experiments were performed from 565 to 515 °C and from 690 to 590 °C. By increasing the deposition temperature, a slight decrease of the migration rate was observed, though a positive impact on the crystal's morphology was also found.}, 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{KnorrIckerEfimovaetal., author = {Knorr, Monika and Icker, Maik and Efimova, Anastasia and Schmidt, Peer}, title = {Reactivity of Ionic Liquids: Studies on Thermal Decomposition Behavior of 1-Butyl-3-methylimidazolium Tetrafluoroborate}, series = {Thermochimica Acta}, volume = {Vol. 694}, journal = {Thermochimica Acta}, issn = {0040-6031}, doi = {10.1016/j.tca.2020.178786}, pages = {1 -- 11}, abstract = {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.}, 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{MeissnerEfimovaSchmidt, author = {Meißner, Andr{\´e} and Efimova, Anastasia and Schmidt, Peer}, title = {Impacts of TGA furnace parameters for prediction of long-term thermal stability of ionic liquids}, series = {Thermochimica Acta}, volume = {704}, journal = {Thermochimica Acta}, doi = {10.1016/j.tca.2021.178917}, pages = {178917-1 -- 178917-7}, abstract = {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.}, language = {en} } @techreport{SchmidtDonathWelsetal., author = {Schmidt, Peer and Donath, Ines and Wels, Martin and Pinnau, Sebastian and Grau Turuelo, Constantino and Breitkopf, Cornelia and Hack, Klaus and Baben, Moritz to and Reis, Bruno and M{\"u}ller, Michael and Sergeev, Dmitry and Qi, Jia}, title = {PCM Screening - Evaluierung eutektischer Gemische f{\"u}r den Einsatz als PCM: thermodynamische Modellierung und experimentelle Methoden : Energie Speicher: PCM-Screening : Schlussbericht}, publisher = {TIB - Leibniz-Informationszentrum Technik und Naturwissenschaften}, address = {Hannover}, doi = {10.2314/KXP:177643451X}, pages = {163}, abstract = {Ein wichtiges Ziel der Bundesregierung ist der Ausbau des Anteils erneuerbarer Energien an der gesamten Stromerzeugung. Die Entwicklung optimierter W{\"a}rme- und K{\"a}ltespeicher stellt einen wichtigen Baustein bei der Erreichung dieser Zielstellung dar. Elektrisch betriebene W{\"a}rmepumpen und Kompressionsk{\"a}ltemaschinen sowie dezentrale Klein-BHKW bieten in Verbindung mit entsprechend dimensionierten, thermischen Speichern ein großes Potential zum Lastmanagement in Smart Grids und somit zur Netzintegration von Strom aus erneuerbaren Energien. Die im Projekt entwickelte Methodik zur Suche nach neuen Latentspeichermedien kann f{\"u}r ein breites Anwendungsfeld von Heiz- und K{\"u}hlanwendungen in Geb{\"a}uden bis hin zur Kraftwerkstechnik eingesetzt werden. Innerhalb der F{\"o}rdermaßnahme „Anwendungsorientierte Forschung und Entwicklung zur nichtnuklearen Energieforschung" im 6. Energieforschungsprogramm der Bundesregierung wurde durch die Projektarbeiten das Schwerpunktthema Energiespeicher (3.8) adressiert, wobei der Aspekt der Entwicklung neuer Materialien mit reduzierten Kosten f{\"u}r einen wirtschaftlichen Betrieb im Vordergrund stand. Speziell wurden dabei die Unterpunkte 3.8.4 Thermische Speicher zur Weiterentwicklung, Optimierung und Erprobung von PCM sowie 3.8.5 {\"U}bergeordnete Themen mit Modellen und Simulationswerkzeugen f{\"u}r die Auswahl und Bewertung neuer Speichermaterialien adressiert. Die Projektergebnisse besitzen aber auch Ber{\"u}hrungspunkte mit den Schwerpunkten 3.12 Energieeffizienz in Industrie, Gewerbe, Handel und Dienstleistungen sowie 3.4 Solarthermische Kraftwerke, da mit der entwickelten Screening-Methode f{\"u}r diese Anwendungsf{\"a}lle neue W{\"a}rmespeichermaterialien auf der Basis wasserfreier Salze mit h{\"o}heren Prozesstemperaturen gefunden werden k{\"o}nnen. Durch den Einsatz von Methoden zur Modellierung und Simulation von Prozessen erfolgt gleichermaßen die Umsetzung einer energie- und ressourcenschonenden Forschungst{\"a}tigkeit. Das im Projekt entwickelte Vorgehen hilft dabei, einen {\"a}ußerst sparsamen Einsatz von Chemikalien, eine niedrige Belastung der Umwelt durch verringerten Entsorgungsaufwand der verbrauchten Stoffe sowie einen deutlich geringeren Aufwand und Energieeinsatz f{\"u}r die Messtechnik zu erm{\"o}glichen. Damit wurde zugleich das Schwerpunktthema 3.8.5 Modelle und Simulationswerkzeuge f{\"u}r die Auswahl und Bewertung neuer Speichermaterialien angesprochen.}, language = {de} } @misc{EhrlingSenkovskaEfimovaetal., author = {Ehrling, Sebastian and Senkovska, Irena and Efimova, Anastasia and Bon, Volodymyr and Abylgazina, Leila and Petkov, Petko and Evans, Jack D. and Attallah, Ahmed Gamal and Wharmby, Michael Thomas and Roslova, Maria and Huang, Zhehao and Tanaka, Hideki and Wagner, Andreas and Schmidt, Peer and Kaskel, Stefan}, title = {Temperature Driven Transformation of the Flexible Metal-Organic Framework DUT-8(Ni)}, series = {Chemistry - a European journal}, volume = {28}, journal = {Chemistry - a European journal}, number = {55}, issn = {1521-3765}, doi = {10.1002/chem.202201281}, pages = {1 -- 10}, abstract = {DUT-8(Ni) metal-organic framework 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 an 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 cp to ccp 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.}, language = {en} } @misc{FroeschkeWolfHantuschetal., author = {Froeschke, Samuel and Wolf, Daniel and Hantusch, Martin and Giebeler, Lars and Wels, Martin and Gr{\"a}ßler, Nico and B{\"u}chner, Bernd and Schmidt, Peer and Hampel, Silke}, title = {Synthesis of micro- and nanosheets of CrCl3-RuCl3 solid solution by chemical vapour transport}, series = {Nanoscale}, volume = {29}, journal = {Nanoscale}, number = {14}, issn = {2040-3372}, doi = {10.1039/D2NR01366E}, pages = {10483 -- 10492}, abstract = {Solid solutions of 2D transition metal trihalides are rapidly growing in interest for the search for new 2D materials with novel properties at nanoscale dimensions. In this regard, we present a synthesis method for the Cr1-xRuxCl3 solid solution and describe the behaviour of the unit cell parameters over the whole composition range, which in general follows Vegard's law in the range of a = 5.958(6)CrCl3 … 5.9731(5)RuCl3 {\AA}, b = 10.3328(20)CrCl3 … 10.34606(21)RuCl3 {\AA}, c = 6.110(5)CrCl3 … 6.0385(5)RuCl3 {\AA} and β = 108.522(15)CrCl3 … 108.8314(14)RuCl3 °. The synthesized solid solution powder was subsequently used to deposit micro- and nanosheets directly on a substrate by applying chemical vapour transport in a temperature gradient of 575 °C → 525 °C for 2 h and 650 °C → 600 °C for 0.5 h as a bottom-up approach without the need for an external transport agent. The observed chromium chloride enrichment of the deposited crystals is predicted by thermodynamic simulation. The results allow for a nanostructure synthesis of this solid solution with a predictable composition down to about 30 nm in height and lateral size of several μm. When applying a quick consecutive delamination step, it is possible to obtain few- and monolayer structures, which could be used for further studies of downscaling effects for the CrCl3-RuCl3 solid solution. X-ray photoelectron spectroscopy, transmission electron microscopy and Raman spectroscopy were used to confirm the purity and quality of the synthesized crystals.}, 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{BoehlerRosencrantzWolfetal., author = {B{\"o}hler, Stefan and Rosencrantz, Sophia and Wolf, Karina and Heinemann, Robert and Schmidt, Peer and Ganster, Johannes and B{\"u}sse, Thomas and Balko, Jens and Rosencrantz, Ruben R.}, title = {Active protease formulation in commodity polymers withstands melt processing into compounds and blown films}, series = {Materials Today Communications}, volume = {34}, journal = {Materials Today Communications}, issn = {2352-4928}, doi = {10.1016/j.mtcomm.2022.105018}, pages = {1 -- 9}, abstract = {Integrating enzymes into thermoplastic polymers is challenging due to their lack of robustness with respect to temperature and shear fields during conventional melt processing. In the present study, blown films from low-density polyethylene (LDPE) were prepared containing a technical protease from Bacillus sp. First, LDPE/protease compounds were produced followed by blown film extrusion, both processes at melt mass temperatures of 130 °C or higher. Enzyme activity was proven, both for the LDPE/protease compound and the blown film. The highest enzyme activity in the compound was determined for processing at 132 °C and a screw speed of 75 rpm. The influence of melt temperature and shear fields was studied in detail. Enzyme activities were determined for melt temperatures up to 160 °C and for screw speeds ranging from 75 to 300 rpm during compounding by twin-screw extrusion. The process was also applied for biobased and biodegradable polyesters, where similar protease activity after compounding was verified. Electron microscopy, X-ray diffraction, nuclear magnetic resonance spectroscopy and differential scanning calorimetry served to analyze components and morphology of the enzyme formulation used here. It is proposed that the porous morphology of the protease particles is beneficial for the enzyme to remain active after processing. Additionally, the polymer matrix surrounding the particles protects the protease at elevated temperatures, which can be attributed to thermal insulation. Thus, the right combination of a suited technical enzyme formulation with appropriate mild melt compounding conditions allows enzymes to be incorporated into thermoplastics and retain their activity. This opens the way to use the abundant biological functions of enzymes in thermoplastic applications.}, language = {en} } @misc{FroeschkeBesthaFuckeetal., author = {Froeschke, Samuel and Bestha, Kranthi Kumar and Fucke, Rico and Schiemenz, Sandra and Popov, Alexey and Naumann, Marco and Knupfer, Martin and Giebeler, Lars and Wolf, Daniel and Kizhake Malayil, Ranjith Kumar and Sivan, Saramgi Chencheriparambil and Grafe, Hans-Joachim and Gräßler, Nico and Corredor, Laura T. and Wolter, Anja U. B. and B{\"u}chner, Bernd and Schmidt, Peer and Hampel, Silke}, title = {Structural and Magnetic Transitions Caused by Dimer Formation in the CrCl3-MoCl3 Solid Solution}, series = {Chemistry of Materials}, volume = {36}, journal = {Chemistry of Materials}, number = {9}, issn = {0897-4756}, doi = {10.1021/acs.chemmater.3c03109}, pages = {4240 -- 4253}, abstract = {In this work, we apply the concept of solid solutions to the two 2D transition metal trihalides CrCl3 and MoCl3. While CrCl3 belongs to the magnetically active CrX3 family, the magnetism in MoCl3 is intrinsically suppressed by the formation of aligned Mo-Mo dimers, which also distort the regular honeycomb lattice that is typical for the 2D transition metal trihalides. We report suitable synthesis conditions for the gapless solid solution and crystal growth by chemical vapor transport. The CrCl3-MoCl3 solid solution was initially synthesized at 650 °C for 100 h under addition of MoCl5 as mineralizer, and bulk crystals were subsequently grown by vapor transport in a temperature gradient from 600 °C → 550 °C for 60 h. The obtained solid solution exhibits multiple composition-dependent phase transitions at room temperature, as confirmed by powder X-ray diffraction measurements. The possible presence of Mo-Mo dimers in the solid solution was further investigated by infrared, Raman, electron energy loss, and nuclear quadrupole resonance spectroscopies. The combined results indicate that the Mo-Mo dimers are present over a wide range of compositions. Their orientation changes from parallel alignment for compositions from 70\% ≤ c(Mo3+) ≤ 100\% to random orientation for samples with c(Mo3+) < 70\% content, which significantly affects the course of lattice parameters. Finally, the magnetic properties of the powder samples show a correlation between the Mo3+ content and the transition temperature into the low-temperature phase.}, language = {en} } @misc{FroeschkeYasmenPopovetal., author = {Froeschke, Samuel and Yasmen, Nadia and Popov, Alexey and Schiemenz, Sandra and Wolf, Daniel and Giebeler, Lars and Hantusch, Martin and Gr{\"a}ßler, Nico and B{\"u}chner, Bernd and Schmidt, Peer and Hampel, Silke}, title = {Controlled Nanoplatelet Deposition of 2D Chromium Trihalide Solid Solutions}, series = {Chemistry of Materials}, volume = {35}, journal = {Chemistry of Materials}, number = {11}, issn = {1520-5002}, doi = {10.1021/acs.chemmater.2c03785}, pages = {4136 -- 4148}, abstract = {The two-dimensional (2D) chromium trihalides CrCl3, CrBr3, and CrI3 are most famous for their exotic magnetic properties when their crystals get downscaled to nanometer dimensions. One way to tune the properties of such materials and to further increase their potential utility, e.g., in spintronics, is the formation of solid solutions. Here, we present a detailed theoretical and experimental study on the synthesis and nanoplatelet growth of CrBrxCl3-x and CrBrxI3-x solid solutions. Phase pure powder was obtained by tempering the respective parent compounds at 600 and 550 °C, using additional iodine in the case of CrBrxI3-x. The dominant stacking order changes at x = 1.8 for CrBrxCl3-x while remaining similar to CrI3 for the whole CrBrxI3-x series. A consecutive chemical vapor transport from 575 → 525 °C for 2 h (CrBrxCl3-x) or 600 → 550 °C for 3 h with 0.1 mmol additional iodine (CrBrxI3-x) resulted in the deposition of high-quality nanoplatelets on a substrate with only several nanometers in height. The composition can be controlled by the choice of the starting material, since only small shifts in the anion ratio occur during the transport. The deposited CrBrxCl3-x nanoplatelets can then be easily delaminated by ultrasonication in ethanol to reduce the height even further to few-layer dimensions. These nanoplatelets could potentially be used to investigate the property changes (e.g., in terms of magnetic response) for the downscaling of these solid solutions. We further demonstrate the quality of the deposited material by transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectroscopy. Raman spectroscopy of the solid solution series reveals a complex evolution of vibrational modes. Photoluminescence measurements on solid solution samples show emission peaks in the near-infrared energy range with the specific energy and intensity being composition and temperature dependent.}, language = {en} } @misc{FroeschkeSchrothSteineretal., author = {Froeschke, Samuel and Schroth, Karl-Georg and Steiner, Udo and Popov, Alexey and Schiemenz, Sandra and Wolf, Daniel and Giebeler, Lars and Gr{\"a}ßler, Nico and B{\"u}chner, Bernd and Schmidt, Peer and Hampel, Silke}, title = {Understanding the chemistry of 2D rhodium trihalide solid solutions: tuning of optical properties and nanocrystal deposition}, series = {2D Materials}, volume = {10}, journal = {2D Materials}, number = {3}, issn = {2053-1583}, doi = {10.1088/2053-1583/acd012}, pages = {1 -- 12}, abstract = {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: RhBrxCl3-x and RhBrxI3-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 RhBrxCl3-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 RhBrxI3-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.}, language = {en} } @misc{VinokurovaKnorrEfimovaetal., author = {Vinokurova, Ekaterina and Knorr, Monika and Efimova, Anastasia and Ovchinnikov, Alexander and Schmidt, Peer and B{\"u}chner, Bernd and Isaeva, Anna and Roslova, Maria}, title = {Microstructural evolution of layered K-doped RuCl3 during annealing traced by thermogravimetric analysis and 3D electron diffraction}, series = {Zeitschrift f{\"u}r Anorgische und Allgemeine Chemie}, volume = {649}, journal = {Zeitschrift f{\"u}r Anorgische und Allgemeine Chemie}, number = {19}, issn = {0044-2313}, doi = {10.1002/zaac.202300141}, pages = {1 -- 8}, abstract = {Nanoscale phase separation was induced in the K-doped RuCl3 van der Waals material by annealing, and studied with the goal to find a natural design strategy for the formation of two-dimensional architectures as an alternative to the costly and time-consuming experimental artificial growth methods. Phase conversion was traced by means of thermogravimetric analysis combined with mass spectrometry. The local crystal structure of co-existing K3Ru2Cl9 domains with the sizes of about 100 nm was solved by 3D electron diffraction.}, 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} } @misc{MichalkBartholomaeusSchmidt, author = {Michalk, Silke and Bartholom{\"a}us, Heike and Schmidt, Peer}, title = {Von starren Grenzen zu freien Wegen : die Entfaltung von Bildungspotenzialen}, series = {University:Future Festival (U:FF), 13. bis 15. Mai 2025}, journal = {University:Future Festival (U:FF), 13. bis 15. Mai 2025}, abstract = {Wie kann Studium neu gedacht werden? Die BTU Cottbus-Senftenberg diskutiert ein zukunftsf{\"a}higes Hochschulmodell, das Profillinien, Microcredentials und Future Skills integriert. Im Rahmen der Neugestaltung der Rahmenstudienordnungen und im Kontext der Empfehlungen des Wissenschaftsrates zur Weiterentwicklung des Hochschulsystems Brandenburg entsteht ein zukunftsf{\"a}higes Hochschulmodell, das Durchl{\"a}ssigkeit, Flexibilit{\"a}t und Qualit{\"a}t vereint. Der Transformationsprozess setzt auf die Schaffung individueller Bildungswege entlang des gesamten, weiter gefassten Student Life Cycles, wodurch die Attraktivit{\"a}t des Studiums und der Studienerfolg gesteigert werden.}, language = {de} } @techreport{SchmidtGieseHeinemannetal., author = {Schmidt, Peer and Giese, Marie and Heinemann, Robert and Nawdiyal, Amruta and Knorr, Monika and Breitkopf, Cornelia and Schneegans, Marcel Felix and Pinnau, Sebastian and Lorenz, Tommy and Mickoleit, Erik and to Baben, Moritz and Keuter, Philipp and M{\"u}ller, Michael and Sergeev, Dmitry and Ewaznezhad Fard, Darya and Morsa, Amedeo and Rhys, Dominic Jacob and Yazhenskikh, Elena}, title = {PCM-Screening-2 : Evaluierung eutektischer Gemische f{\"u}r den Einsatz als PCM : thermodynamische Modellierung und experimentelle Methoden - 2}, series = {Deutsche Forschungsberichte}, journal = {Deutsche Forschungsberichte}, doi = {10.34657/28504}, pages = {182}, abstract = {Durch den Einsatz von W{\"a}rme- und K{\"a}ltespeichern in Geb{\"a}uden, Industrieanlagen und Kraftwerken k{\"o}nnen Lastschwankungen reduziert und die Anlageneffizienz verbessert werden. Latentw{\"a}rmespeicher (PCM) erm{\"o}glichen durch Ausnutzung einer fest-fl{\"u}ssig Phasenumwandlung hohe Speicherdichten bei geringen Temperaturdifferenzen. Die Verf{\"u}gbarkeit geeigneter und kosteng{\"u}nstiger PCM's ist derzeit noch eingeschr{\"a}nkt. Ein Screening geeigneter Stoffsysteme zur Bildung multin{\"a}rer Eutektika durch thermodynamische Modellierung der Phasengleichgewichte erlaubt fundierte Vorhersagen zur Zusammensetzung eutektischer Gemische, ihren Schmelztemperaturen und -enthalpien. Auf Basis der Literatur, umfangreicher experimenteller Untersuchungen und Simulationen wurde im Projekt eine im Temperaturbereich nicht eingeschr{\"a}nkte thermochemische Datenbank f{\"u}r das komplexe Stoffsystem Na+, K+, Ca2+, Mg2+ // Cl-, NO3-, SO4_2-, CO3_2- // H2O geschaffen, die eine Auswahl neuer PCM mit optimalen thermodynamischen Eigenschaften f{\"u}r spezifische Prozessanforderungen auf Basis von in Deutschland in großen Mengen verf{\"u}gbaren, preiswerten Rohstoffen erm{\"o}glicht. Weiterhin wurde ein CalPhaD-basiertes Viskosit{\"a}tsmodell, ein Screening-Verfahren inkl. Webserver und intuitive Visualisierungsm{\"o}glichkeiten hochkomponentiger Systeme entwickelt. Mittels eines Screenings erfolgte eine Vorauswahl von potentiell als PCM geeigneten Gemischen, die umfangreich charakterisiert wurden. Auf Basis der vielversprechenden Speicherdichten und der niedrigen Materialkosten wird erwartet, dass ein oder mehrere dieser identifizierten PCMs in die Anwendung als thermische Speicher gebracht werden k{\"o}nnen.}, language = {de} }