Search results for "Absorption"
showing 10 items of 2701 documents
EPR studies of Mn, Fe, Co, and Cu doped PLZT and PMN compositions
1993
Results of Mn, Fe, Co, and Cu admixture EPR spectra studies in PLZT and PMN ceramics are discussed. The spectra of Mn, Fe, and Co ions with dominating absorption at geff = 2.0 and 4.3 are proposed due to d5 (S = 5/2) configurations (Mn2+, Fe3+, Co4+). The latter can be used as probes disclosing specific features (glass-like behaviour) of the structures. The Jahn-Teller ions (Mn3+, Fe4+, Co5+, Cu2+) are responsible for the dopant effect, e.g., the shift of the e(T) maximum to higher temperatures. The microscopic nature of differences of the dopant effect in PLZT and PMN materials and in the Mn Fe Co sequence is analyzed. [Russian Text Ignored].
Effects of Ionising Radiation on Optical Properties of Lithium Niobate Single Crystals
2005
Studies of thermal and γ-irradiation effects on the optical properties in congruent lithium niobate single crystals containing Mg and Gd dopants including samples with double dopants Y, Mg are reported. Formation of defects at irradiation and thermal treatment of the samples is explored by analysis of the behaviour of electron absorption spectra. Considerable increase of absorption with the dose of γ-radiation is observed at 500 nm. The changes of absorption examined under different conditions are explained by creation and destruction of Nb 4+ defects.
Effect of oxygen deficiency on the radiation sensitivity of sol-gel Ge-doped amorphous SiO2
2008
We report experimental investigation by electron paramagnetic resonance (EPR) measurements of room temperature γ-ray irradiation effects in sol-gel Ge doped amorphous SiO2. We used materials with Ge content from 10 up to 104 part per million (ppm) mol obtained with different preparations. These latter gave rise to samples characterized by different extents of oxygen deficiency, estimated from the absorption band at ~5.15 eV of the Ge oxygen deficient centers (GeODC(II)). The irradiation at doses up to ~400 kGy induces the E'-Ge, Ge(1) and Ge(2) paramagnetic centers around g ~ 2 with concentrations depending on Ge and on GeODC(II) content. We found correlation between Ge(2) and GeODC(II) con…
Water diffusion and swelling stresses in highly crosslinked epoxy matrices
2016
Abstract The present work investigates the swelling induced stresses arising in two epoxy systems during water uptake. The analysed systems are two epoxy resin based on DGEBA monomer and DGEBF monomer respectively, both fully cured by DDS amine. The systems achieve different cross-link density degrees, and are characterised by high glass transition temperatures ranging between 200 and 230 °C. Both epoxies have been conditioned in deionized water baths at two different temperatures (50 °C and 80 °C). A desorption process at room temperature in a dry airborne environment was performed after saturation. Dynamic Mechanical Thermal Analysis, carried out at the various stages of hydrothermal cond…
Structural and CO [sub] 2 capture properties of ethylenediamine-modified HKUST-1 metal-organic framework
2020
The high structural and compositional flexibility of metal–organic frameworks (MOFs) shows their great potential for CO2 capture and utilization in accordance with the environmental guidelines of low-carbon technology developments. HKUST-1 as one of the most intensively studied representatives of MOFs for such purposes excels because of its simplicity of production and high ability to tune its intrinsic properties by various functionalization processes. In the present work, ethylenediamine functionalization was performed for the first time in order to thoroughly investigate the amine sorption sites’ impact on the CO2 capture performance of HKUST-1. The placement of ethylenediamine moieties …
Local structure of copper nitride revealed by EXAFS spectroscopy and a reverse Monte Carlo/evolutionary algorithm approach
2016
Physica scripta 91(5), 054003 (2016). doi:10.1088/0031-8949/91/5/054003
Low Temperature Optical Absorption by Magnons in KNiF3 and NiO Single-Crystals
2000
Optical absorption spectra of KNiF3 and NiO stoichiometric single-crystals were measured at 5 K in the range from 4000 to 50000 cm-1. The observed bands are interpreted based on the energy levels diagram for Ni2+ (3d 8 ) ion in a cubic crystal field. The crystal-field parameter Dq is equal to 766 cm-1 in KNiF3 and 890 cm-1 in NiO. Particular attention is paid to the band due to the magnetic-dipole 3A2g(F)→3T2g(F) transition, located at 7700 cm-1 in KNiF3 and at 8900 cm-1 in NiO. We show that the energy difference between the two peaks, located at the low energy side of the band, is related to the zone-center (k=0) one-magnon energy, so that the low-energy peak is attributed to the pure exci…
Molecular dynamics and reverse Monte Carlo modeling of scheelite-type AWO4(A = Ca, Sr, Ba) WL3-edge EXAFS spectra
2016
Classical molecular dynamics (MD) and reverse Monte Carlo methods coupled with ab initio multiple-scattering extended x-ray absorption fine structure (EXAFS) calculations were used for modeling of scheelite-type AWO4 (A = Ca, Sr, Ba) W L 3-edge EXAFS spectra. The two theoretical approaches are complementary and allowed us to perform analysis of full EXAFS spectra. Both methods reproduce well the structure and dynamics of tungstates in the outer coordination shells, however the classical MD simulations underestimate the W–O bond MSRD due to a neglect of quantum zero-point-motion. The thermal vibration amplitudes, correlation effects and anisotropy of the tungstate structure were also estimat…
Effect of Pressure and Temperature on the Local Structure and Lattice Dynamics of Copper(II) Oxide
2016
Abstract Microcrystalline and nanocrystalline (6 nm) CuO were studied in situ by the Cu K-edge X-ray absorption spectroscopy as a function of pressure (0-20 GPa) and temperature (10-300 K). Pressure dependence of X-ray absorption near edge structure (XANES) was interpreted within the full-multiple-scattering formalism based on the relaxed atomic structure determined by ab initio linear combination of atomic orbital (LCAO) calculations. Temperature dependence of the mean-square relative displacement (MSRD) for the four shortest Cu–O distances was obtained from the analysis of extended X-ray absorption fine structure (EXAFS) and described by the correlated Einstein model with the characterist…
Optical, X-ray absorption and photoelectron spectroscopy investigation of the Co site configuration in Zn1−xCoxO films prepared by pulsed laser depos…
2007
Abstract In this paper, we investigate the Co site configuration in Zn1−xCoxO thin films by means of different spectroscopic techniques. Thin films were prepared by pulsed laser deposition with Co proportion from 1% to 30%. The Co 2p doublet observed in the X-ray photoelectron spectra exhibits the spin–orbit splitting and shake-up satellites typical of Co+2 ionization states. X-ray absorption spectra at the Co K-edge, taken in fluorescence mode, unambiguously show that Co atoms are in tetrahedral configuration substituting for Zn over the whole composition range. Optical absorption spectra provide further evidence of the tetrahedral coordination of Co cations, both through the internal tran…