Lattice dynamics and structure of the new langasites Ln3CrGe3Be2O14 (Ln ¼ La, Pr, Nd): Vibrational spectra and ab initio calculations
We present experimental (by means of the infrared absorption and Raman scattering measurements at room
temperature) and first-principles studies of the lattice dynamics of the recently discovered new compounds
La3CrGe3Be2O14, Pr3CrGe3Be2O14, and Nd3CrGe3Be2O14 belonging to the langasite series and constituting a new
class of low-dimensional antiferromagnets. The observed vibrational modes of all the three compounds are
consistent with the results of the group-theoretical analysis for the langasite structure (sp. gr. P321) established
earlier for La3CrGe3Be2O14 by the Rietveld refinement. Vibrational frequencies are uniformly distributed over the
spectral range ~80–840 cm 1. Frequencies and intensities of the modes were satisfactory modeled in the
framework of density functional theory and MO LKAO approach using the B3LYP hybrid functional which takes
into account the non-local exchange in the Hartree-Fock formalism. Analyzing the displacement vectors obtained
in the ab initio calculations, we estimate the degree of participation of each ion in each vibrational mode. Information
on the lattice dynamics of the title compounds is essential for a further research on the properties and
functionalities of these new low-dimensional magnets with frustrated interactions.
Despite the increased interest in Chinese export painting of the XVIII–XIX centuries, the research of it had found its reflection particularly in description of this art form history, its cultural component, in description of myriads collections stored in the funds of museums, archives and libraries around the world, collectors and their interests and journeys to China. However, artistic techniques and materials utilized by Chinese masters can also become a source of valuable information on cultural and economic cooperation between the two great civilizations - Chinese and Western. In this regard, domestic and foreign scholars commenced conducting researches involving modern methods of image analysis in the study of Chinese export painting. These methods include reflection and polarized microscopy, electron microscopy, as well as non-destructive techniques, such as multi-spectral analysis, optical coherence tomography (OCT), microfade spectrometry, Raman spectroscopy and X-ray fluorescence spectroscopy (XRF).
In this work we present the results of in-situ case studies of fuel oxidation at the SOFC anode for anode-supported cells with thinfilm electrolyte deposited by magnetron sputtering technique in comparison with studies carried out on optically transparent singlecrystal membrane based electrolyte-supported model SOFC. Changes of the valence state of Ce ions were studied under different current loads applied to the cell, these changes were indicated in the Raman spectra obtained from inner interface of electrolyte membrane and anode electrode. Area of the corresponding peak in Raman spectra of ceria was studied for different working conditions for both cells constructions. Special processing technique gave opportunity to obtain more relevant data.
A novel experimental approach for in-situ Raman spectroscopy of the electrode I solid electrolyte interfaces in controlled atmospheres, based on use of the optically transparent single-crystal membranes of stabilized cubic zirconia, was proposed and validated. This technique makes it possible to ditectly access the electrochemical reaction zone in SOFCs by passing laser beam through the single-crystal electrolyte onto the interface, in combination with simultaneous electrochemical measurements. The case study centered on the analysis of NiO reduction in standard cermet anodes under open-circuit conditions, demonstrated an excellent agreement between the observed kinetic parameters and literature data on nickel oxide. The porous cermet reduction kinetics at 400-600 degrees C in flowing H-2-N-2 gas mixture can be described by the classical Avrami Model, suggesting that the reaction rate is determined by metal nuclei growth limited by Ni diffusion. The advantages and limitations of the technique are briefly addressed.
Optical phonons in nanoparticles with randomness of interatomic bonds are considered both analytically and numerically. For weak dilute disorder, two qualitatively different regimes of separated and overlapped levels are observed, resembling the case of random atomic masses investigated previously. At stronger and/or more dense disorder, the particles become essentially inhomogeneous, thus constituting a minimal model to describe an amorphous phase, where the picture of vibrational modes becomes more subtle. We concentrate here on the experimentally relevant case of a strong disorder located near the particle surface and formulate the core-shell model aimed to describe the ubiquitous phenomenon of particle surface amorphization. We observe a peculiar effect of volume optical phonons “repelling” from the disordered shell. It results in the Raman spectrum appearing in the form of a combination of narrow well-resolved peaks stemming from the quantized modes of a pure particle core (red-shifted due to its effective smaller size) and a wide pedestal-like signal from the disordered shell, placed primarily to the right of the main Raman peak.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.
This volume presents new results in the study and optimization of information transmission models in telecommunication networks using different approaches, mainly based on theiries of queueing systems and queueing networks .
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.