@misc{GaraiBonEfimovaetal., author = {Garai, Bikash and Bon, Volodymyr and Efimova, Anastasia and Gerlach, Martin and Senkovska, Irena and Kaskel, Stefan}, title = {Reversible switching between positive and negative thermal expansion in a metal-organic framework DUT-49}, series = {Journal of Materials Chemistry A}, volume = {39}, journal = {Journal of Materials Chemistry A}, number = {8}, issn = {2050-7496}, doi = {10.1039/D0TA06830F}, pages = {20420 -- 20428}, abstract = {Three-dimensional architectures constructed via coordination of organic ligands to metal ions (broadly termed metal-organic frameworks, MOFs), are highly interesting for many demanding applications such as gas adsorption, molecular separation, heterogeneous catalysis, molecular sensing, etc. Being constructed from heterogeneous components, such framework solids show characteristic features from both the individual components and framework-specific features. One such interesting physicochemical property is thermal expansion, which arises from thermal vibration from the organic linker and metal ions. Herein, we show a very unique example of thermal responsiveness for the DUT-49 framework, a MOF well-known for its distinctive negative gas adsorption (NGA) properties. In the guest-free form, the framework shows another counter-intuitive phenomenon of negative thermal expansion (NTE), i.e. the lattice size increases with decrease of temperature. However, in the solvated state, it shows both NTE and positive thermal expansion (i.e. lattice size decreases with lowering of temperature, PTE) based on a specific temperature range. When the solvent exists in the liquid form inside the MOF pore, it retains the pristine NTE nature of the bare framework. But freezing of the solvent inside the pores induces the strain, which causes a structural transformation through in-plane bending of the linker and this squeezes the framework by ∼10\% of the unit cell volume. This effect has been verified using 3 different solvents where the structural contraction occurs immediately at the freezing point of the individual solvent. Furthermore, studies on a series of DUT-49(M) frameworks with varying metals confirm the general applicability of this mechanism.}, 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{KlepelUtgenanntVormelchertetal., author = {Klepel, Olaf and Utgenannt, Stephan and Vormelchert, Carolin and K{\"o}nig, Mark and Meißner, Andr{\´e} and Hansen, Felix and B{\"o}lte, Jens-Henning Ingo Holger and Sieber, Tim and Heinemann, Robert and Bron, Michael and Rokicinska, Anna and Jarczewski, Sebastian and Kustrowski, Piotr}, title = {Redox catalysts based on amorphous porous carbons}, series = {Microporous Mesoporous Materials}, volume = {323}, journal = {Microporous Mesoporous Materials}, issn = {1387-1811}, doi = {10.1016/j.micromeso.2021.111257}, pages = {12}, 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} } @misc{IvshinMetlushkaZinnatullinetal., author = {Ivshin, Kamil and Metlushka, Kirill and Zinnatullin, Ruzal and Nikitina, Kristina and Pashagin, Alexander and Zakharychev, Dmitry V. and Efimova, Anastasia and Kiiamov, Airat and Latypov, Shamil and Kataeva, Olga}, title = {Competitive Hydrogen Bonding and Unprecedented Polymorphism in Selected Chiral Phosphorylated Thioureas}, series = {Crystal Growth Design}, volume = {21}, journal = {Crystal Growth Design}, number = {9}, issn = {1528-7505}, doi = {10.1021/acs.cgd.1c00758}, pages = {5460 -- 5471}, abstract = {New racemic and enantiopure N-phosphorylated thioureas bearing 1-phenylethyl or tetrahydronaphthalenyl fragments were synthesized. According to NMR data assisted by DFT calculations, the preferred conformation is stabilized by an intramolecular hydrogen bond. This form in solution is in equilibrium with dimeric N-H···S hydrogen-bonded associates, the population depending on the concentration. In the crystalline phase the low-energy conformation with an intramolecular H-bond is realized only in the racemic tetrahydronaphthalenyl derivative. In most crystals various types of intermolecular hydrogen bonding are observed, accompanied by the formation of infinite linear chains or helical structures. Due to the conformational lability of compounds and competitive intermolecular H-bonding, multiple polymorphic modifications are formed. Therefore, crystallization of enantiopure 1-phenylethyl derivatives from various solvents results in concomitant polymorphs at room temperature. One of them undergoes reversible two-step phase transitions from the high-symmetry I41 space group (Z′ = 1, no disorder) via the P41 space group (Z′ = 6) to the monoclinic P21 space group (Z′ = 16) accompanied by drastic concerted conformational changes. Notably, the optimization of the crystal packing is observed upon phase transitions with a gradual reduction of the void space in the unit cell from 4.5\% to 0.8\%. This is a rare case of several high-Z′ polymorphs for one compound, with chirality playing an important role.}, 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} }