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Spontaneous ferroelectric order in lead-free relaxor, -based composites
No full textShort-range ordered polar nanoregions are key to the giant electromechanical properties exhibited by relaxor ferroelectrics. Stabilization of the long-range ferroelectric order in relaxor systems has typically been achieved by applying external fields. In this work, spontaneous (zero-field) ferroelectric order is demonstrated in the composites constituting of nonergodic relaxor matrix phase 0.91NaBiTiO−0.09BaTiO with ZnO inclusions. Direct structural evidence is provided for the long-range ferroelectric order in the composites using in situ electric-field-dependent synchrotron investigations and 23Na nuclear magnetic resonance spectroscopy. Thermodynamic analysis incorporating microelasticity reveals the role of spatial residual stress in stabilizing the ferroelectric order. The work provides a direct correlation between the stabilized ferroelectric order and enhanced thermal stability, which can be utilized to guide the design of spontaneous long-range order in other relaxor systems
Influence of Titania Synthesized by Pulsed Laser Ablation on the State of Platinum during Ammonia Oxidation
No full textA set of physicochemical methods, including X-ray photoelectron spectroscopy (XPS), X-ray diraction, electron microscopy and X-ray absorption spectroscopy, was applied to study Pt/TiO2 catalysts prepared by impregnation using a commercial TiO2-P25 support and a support produced by pulsed laser ablation in liquid (PLA). The Pt/TiO2-PLA catalysts showed increased thermal stability due to the localization of the highly dispersed platinum species at the intercrystalline boundaries of the support particles. In contrast, the Pt/TiO2-P25 catalysts were characterized by uniform distributionof the Pt species over the support. Analysis of Pt4f XP spectra shows that oxidized Pt2+ and Pt4+ species are formed in the Pt/TiO2-P25 catalysts, while the platinum oxidation state in the Pt/TiO2-PLA catalysts is lower due to stronger interaction of the active component with the support due to stronginteraction via Pt-O-Ti bonds. The Pt4f XP spectra of the samples after reaction show Pt2+ and metallic platinum, which is the catalytically active species. The study of the catalytic properties in ammonia oxidation showed that, unlike the catalysts prepared with a commercial support, the Pt/TiO2-PLA samples show higher stability during catalysis and significantly higher selectivity to N2 in a wide temperature range of 200–400 C
Axion-mediated forces and CP violation in left-right models
No full textWe compute the CP-violating (CPV) scalar axion coupling to nucleons in the framework of baryon chiral perturbation theory and we apply the results to a class of left-right symmetric models. The correlated constraints with other CPV observables show that the predicted axion nucleon coupling is within the reach of axion-mediated force experiments as ARIADNE for up to TeV
Untersuchung der Photoelektronen-Winkelverteilungen von ausgerichteten Molekülen in der Gasphase
No full textThis work investigates if and how photoelectron diffraction might become a suitable tool to measure structural changes of small molecules in the gas-phase with femtosecond temporal and angstrom spatial resolution. Molecular-frame photoelectron angular distributions (MFPAD) of O(1)-, S(2)- and F(1)-electrons from carbonyl sulfide and fluoromethane molecules have been measured in photoelectron-photoion coincidence experiments at the synchrotron radiation sources DORIS and PETRA III (kinetic energy of photoelectrons: 16 eV < E < 283 eV). It has been investigated which degree of molecular orientation is necessary to observe a rich structure in the MFPADs, which influence linearly and circularly polarized photons have on MFPADs, and if MFPADs of photoelectrons with a few 100 eV kinetic energy can be described by a simple scattering model.The relation of the measured MFPADs to the molecular structure was examined by MSX calculations. At the free-electron laser FLASH, S(2)-photoelectron angular distributions of adiabatically laser-aligned OCS molecules have been measured (E=44 eV). In an IR-pump-XUV-probe experiment at FLASH, molecular dynamics have been observed in the photoelectron angular distributions with femtosecond temporal resolution. The influence of the alignment and the pump laser on molecules and on photoelectrons has been discussed. This work indicates avenues how to reach the goal of observing ultrafast molecular structural changes by photoelectron diffraction
Intrinsic electronic excitations and impurity luminescent centres in NaMgF and MgF doped with Yb
No full textThe relaxation pathways of states in the energy region of the fundamental absorption of NaMgF and MgF and MgF:Yb are investigated using time-resolved vacuum ultraviolet spectroscopy. ForNaMgF and MgF :Yb, excitation into intrinsic free exciton states or above the band gap results in emission features associated with self-trapped excitons and impurity-trapped excitons. Excitation into host-related states of MgF:Yb similarly exhibits self-trapped exciton emission as well as emission from Yb 4f5d states. The excitation features related to Yb 4f→4f5d transitions are interpreted using semi-empirical crystal field models. For both materials, the interplay between intrinsic distortions and Yb impurity centres, as the excitation wavelength and sample temperature are varied, is presented and analysed
Study of the luminescence of and states in garnet using synchrotron radiation excitation
No full textThe work is dedicated to the investigation of and luminescence centers in the garnet using synchrotron radiation excitation. The luminescence of and states was observed in the emission spectra of :Eu ceramics under excitation with energies in the exciton range and the range above band gap of this garnet. The luminescence of ions host is observed in the band peaked at 450–460 nm with decay time in the ten ns range and excited in the two wide bands peaked at 5.04 and 6.05 eV, related to the allowed 4f-5d transitions of ions. The luminescence can be excited via the luminescence. We have also found the energies of formation of excitons bound with and ions in Ca3Ga2Ge3O12, being equal to 7.64 and 6.95 eV, respectively, and the onset of interband transitions in this garnet which is equal to 7.83 eV at 8 K. Strong increase of the luminescence intensity of and centers is observed under excitation above 21 eV due to multiplication of electronic excitation in host
Structural order in plasmonic superlattices
No full textThe assembly of plasmonic nanoparticles into ordered 2D- and 3D-superlattices could pave the way towards new tailored materials for plasmonic sensing, photocatalysis and manipulation of light on the nanoscale. The properties of such materials strongly depend on their geometry, and accordingly straightforward protocols to obtain precise plasmonic superlattices are highly desirable. Here, we synthesize large areas of crystalline mono-, bi- and multilayers of gold nanoparticles >20 nm with a small number of defects. The superlattices can be described as hexagonal crystals with standard deviations of the lattice parameter below 1%. The periodic arrangement within the superlattices leads to new well-defined collective plasmon-polariton modes. The general level of achieved superlattice quality will be of benefit for a broad range of applications, ranging from fundamental studies of light–matter interaction to optical metamaterials and substrates for surface-enhanced spectroscopies
Study of proton parton distribution functions at high using ZEUS data
No full textAt large values of x, the parton distribution functions (PDFs) of the proton are poorly constrained and there are considerable variations between different global fits. Data at such high x have already been published by the ZEUS Collaboration, but not yet used in PDF extractions. A technique for comparing predictions based on different PDF sets to the observed number of events in the ZEUS data is presented. It is applied to compare predictions from the most commonly used PDFs to published ZEUS data at high Bjorken x. A wide variation is found in the ability of the PDFs to predict the observed results. A scheme for including the ZEUS high-x data in future PDF extractions is discussed
Higgs boson combination and coupling measurements at CMS
No full textThe most recent CMS results on Higgs boson properties from the combination of different final states will be presented, including the Higgs boson mass, couplings, and interpretations in the context of effective field theories extending the standard model