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Probing the temperature induced phase transition mechanism in PbTiO3 BiM0.5Ti0.5O3 ferroelectrics across the morphotropic phase boundary
No full textThe fundamental understanding of the driving mechanism of dipolar ordering in complex perovskite oxides ABO3 and its dependence on the degree of doping as well as on the type of dopant is critical for the effective design of novel functional materials with desired properties. To elucidate the temperature induced transformations in mixed lead bismuth systems, we have studied two solid solutions with a morphotropic phase boundary MPB , 1 amp; 8722; amp; 119909; amp; 8290;PbTiO3 amp; 8722; amp; 119909; amp; 8290;BiNi0.5 amp; 8290;Ti0.5 amp; 8290;O3 PT amp; 119909; amp; 8290;BNT and 1 amp; 8722; amp; 119909; amp; 8290;PbTiO3 amp; 8722;xBiMg0.5 amp; 8290;Ti0.5 amp; 8290;O3 PT amp; 119909; amp; 8290;BMT , by Raman spectroscopy and second harmonic generation SHG . The temperature evolution of atomic dynamics in both PT amp; 119909; amp; 8290;BNT and PT amp; 119909; amp; 8290;BMT shows that the paraelectric to ferroelectric phase transition at the MPB does not involve any dynamical instability, indicating the dominance of order disorder transformation processes. The temperature dependence of the SHG intensity reveals that the MPB can be identified by the smallest size of the preexisting intrinsic ferroic entities that on cooling merge to form a ferroelectric state with a macroscopic polarization. The difference between Ni and Mg containing solid solutions is merely in the correlation length of local structural distortion
Angle resolved photoemission spectroscopy and electrocatalysis is there a bridge in between?
Get PDFThe electronic interaction between molecules and a surface greatly influences the kinetics of heterogeneous electrocatalytic processes. Here, we explore the possibility of using angle resolved photoemission spectroscopy ARPES to study electrocatalysts. Using oxide materials as an example, we identify pitfalls and key challenges of such experiments and discuss future opportunitie
Tuning ultrafast demagnetization with ultrashort spin polarized currents in multi sublattice ferrimagnets
Get PDFFemtosecond laser pulses can be used to induce ultrafast changes of the magnetization in magnetic materials. Several microscopic mechanisms have been proposed to explain these observations, including the transport of ultrashort spin polarized hot electrons SPHE . However, currently such ultrafast spin currents are only poorly characterized due to the measurement requirements for element and time resolution. Here, using time and element resolved X ray magnetic circular dichroism alongside atomistic spin dynamics simulations, we study the ultrafast transfer of the angular momentum from spin polarized currents. We show that using a Co Pt multilayer as a polarizer in a spin valve structure, the SPHE drives the demagnetization of the two sub lattices of the Fe74Gd26 film. This behaviour can be explained with two physical mechanisms; spin transfer torque and thermal fluctuations induced by the SPHE. We provide a quantitative description of the heat transfer of the ultrashort SPHE pulse to the Fe74Gd26 films, as well as the effect of spin polarization of the SPHE current density responsible for the observed magnetization dynamics. Our work finally characterizes the spin polarization of the SPHEs revealing unexpected opposite spin polarization to the Co magnetizatio
Covalent Organic Framework Enhanced Metal Halide Perovskites for Selective and Sensitive Gas Sensing
No full textSolution processed lead free halide perovskite gas sensors possess low gas detection limits, offering promising alternatives to traditional metal oxide chemiresistors. However, halide perovskite chemiresistors often suffer from poor selectivity and durability due to a lack of coordinatively unsaturated surface metal ions and their sensitivity to humidity. To address these issues, a general strategy is presented in which the Cs2PdBr6 perovskite surface is coated with covalent organic framework COF to provide hybrid sensor materials that are highly sensitive to specific gases and demonstrate excellent stability under real working conditions. The hybrid chemiresistors demonstrate high sensitivity and controllable selectivity toward NO2 or NH3 gases. Specifically, TAPB PDA Cs2PdBr6 achieves a detection limit of 10 ppb for NO2, the lowest value reported for a perovskite based gas sensor, maintaining its performance after continuous exposure to ambient air for several weeks. In contrast, COF 5 Cs2PdBr6 shows high selectivity to NH3 and has a detection limit of 40 ppb. Structural and spectroscopic characterization combined with mechanistic studies provide molecular level insights into the outstanding properties of these new hybrid sensor materials, which set a new benchmark in the field, i.e., surpassing the selectivity and sensitivity of conventional halide perovskite sensor
Conformationally Restricted Macrocycles as Improved FKBP51 Inhibitors Enabled by Systematic Linker Derivatization
No full textMacrocycles are increasingly considered as promising modalities to target challenging intracellular proteins. However, strategies for transitioning from active linear starting points to improved macrocycles are still underdeveloped. Here we explored the derivatization of linkers as an approach for macrocycle optimization. Using the FK506 binding protein 51 FKBP51 as a model system we prepared gt;140 macrocycles with systematically derivatized linkers. Two backbones were identified as promising frameworks for subsequent optimization. Surprisingly, co crystal structure analyses revealed that these chemical templates represent an ensemble of three dimensional 3D conformations that can give rise to several distinct 3D scaffolds. This resulted in a set of macrocycles with consistently improved affinity, plasma stability, and aqueous solubility compared to the linear precursors or the non functionalized macrocycles. Our results highlight linkers as an opportunity for macrocyclic drug development, show how linker derivatization can improve the performance of macrocycles, and emphasizes the need to track macrocyclic scaffold evolution at a three dimensional leve
High Temperature Growth of CeOx on Au 111 and Behavior under Reducing and Oxidizing Condition
No full textInverse oxide metal model catalysts can show superior activity and selectivity compared with the traditional supported metal oxide architecture, commonly attributed to the synergistic overlayer support interaction. We have investigated the growth and redox properties of ceria nanoislands grown on Au 111 between 700 and 890 C, which yields the CeO2 Au 111 model catalyst system. We have observed a distinct correlation between deposition temperature, structural order, and oxide composition through low energy electron microscopy, low energy electron diffraction, intensity voltage curves, and X ray absorption spectroscopy. Improved structural order and thermal stability of the oxide have been achieved by increasing the oxygen chemical potential at the substrate surface using reactive oxygen O O2 instead of molecular O2 during growth. In situ characterization under reducing H2 and oxidizing atmospheres O2, CO2 indicates an irreversible loss of structural order and redox activity at high reduction temperatures, while moderate temperatures result in partial decomposition of the ceria nanoislands Ce3 Ce4 to metallic cerium Ce0 . The weak interaction between Au 111 and CeOx would facilitate its reduction to the Ce0 metallic state, especially considering the comparatively strong interaction between Ce0 and Au0. Besides, the higher reactivity of atomic oxygen promotes a stronger interaction between the gold and oxide islands during the nucleation process, explaining the improved stability. Thus, we propose that by driving the nucleation and growth of the ceria Au system in a highly oxidizing regime, novel chemical properties can be obtaine
Reinvestigation of the mechanism of dioxygen activation at a MnII cyclam center
No full textThis study deals with the unprecedented reactivity of a [ cyclam MnII OTf 2] 3 cis; OTf CF3SO3 amp; 8722; with O2, which, depending on the presence or absence of a hydrogen atom donor like 1 hydroxy 2,2,6,6 tetramethyl piperidine TEMPO H , selectively generates di amp; 956; oxo Mn III Mn IV 1 or MnIV2 2 complexes, respectively. Both dimers have been characterized by different techniques including single crystal X ray diffraction, X ray absorption spectroscopy, and electron paramagnetic resonance. Oxygenation reactions carried out with labeled 18O2 and Resonance Raman spectroscopy unambiguously show that the oxygen atoms present in the MnIVMnIII dimer originate from O2. Experimental evidences are provided for a novel method of dioxygen activation involving three Mn ions or two Mn ions and TEMPO H to generate the bis amp; 956; oxo dimanganese IV or bis amp; 956; oxo dimanganese III, IV cores, respectivel
Observation of magnetic skyrmion lattice in Cr0.82Mn0.18Ge by small angle neutron scattering
Get PDFIncommensurate magnetic phases in chiral cubic crystals are an established source of topological spin textures such as skyrmion and hedgehog lattices, with potential applications in spintronics and information storage. We report a comprehensive small angle neutron scattering SANS study on the B20 type chiral magnet Cr0.82Mn0.18Ge, exploring its magnetic phase diagram and confirming the stabilization of a skyrmion lattice under low magnetic fields. Our results reveal a helical ground state with a decreasing pitch from 40 to 35 nm upon cooling, and a skyrmion phase stable in applied magnetic fields of 10 30 mT, and over an unusually wide temperature range for chiral magnets of 6 K amp; 8764; TC 2 lt; T lt; TC, TC 13 K . The skyrmion lattice forms a standard two dimensional hexagonal coordination that can be trained into a single domain, distinguishing it from the three dimensional hedgehog lattice observed in MnGe based systems. Additionally, we demonstrate the persistence of a metastable SkL at 2 K, even at zero field. These findings advance our understanding of magnetic textures in Cr based B20 compounds, highlighting Cr0.82Mn0.18Ge as a promising material for further exploration in topological magnetis
Revealing the history of a Mongolian shrine by virtually unrolling Buddhist Dharanis
Get PDFMongolian Buddhist shrines mong. gungervaa come in a variety of designs, just as the concept of shrines exists across different religions. These shrines are protective containers for icons, such as images or statues of Buddhist teachers, deities, saints, or revered clergy. The central figure is usually surrounded by relics from high ranking lamas as well as decorative offerings presented by worshippers. Since gungervaas are inherited within the family and offerings are added constantly, they can accumulate diverse sets of items over several generations. It is therefore important to examine and analyze the composition inside and understand each single component. One type of object that is found in gungervaas are Dharanis spell scriptures . Physically opening these tiny paper scrolls wrapped in silk poses a risk to their preservation, so it is generally not the preferred method. A non destructive method is needed to decipher the written messages inside. X ray tomography provides a way to examine the interiors of these fragile objects. By creating a three dimensional virtual copy, it was possible to analyze and manipulate the content using computer software without harming the scrolls. Finally, text from inside the Dharanis scrolls was successfully extracted and translate
Photothermal Polarimetric Nanoscopy An Emerging Technique for Fingerprinting Minerals of Extraterrestrial Origin
Get PDFNanospectroscopic investigations of the mineralogical composition of materials returned via sample return missions are crucial for our understanding of the origin and evolution of planetary objects in our Solar System. Here, we show that the emerging technique of photothermal polarimetric nanoscopy, a variant of atomic force microscopy based infrared spectroscopy, enables one to derive infrared fingerprint spectra of minerals noninvasively on the nanoscale. Besides the spatially resolved identification of specific minerals and mineral phases, the evaluation of the polarization dependence of the photoinduced nanomechanical response, in combination with optical reference data, may allow the deduction of valuable structural information on individual nanocrystallites or grains embedded in solid matrice