Search results for "impur"
showing 10 items of 349 documents
Structural fluctuations in glass-forming liquids: Mössbauer spectroscopy on iron in glycerol.
1991
M\"ossbauer absorption spectra of $^{57}\mathrm{Fe}^{2+}$ dissolved in a glycerol-water mixture have been measured over a wide temperature range (80--275 K). In the supercooled liquid state the shapes of the spectra depend strongly on temperature. The M\"ossbauer spectra can be fit with jump diffusion with a Cole-Davidson distribution of fluctuation times. The results are in agreement with those obtained from dielectric and ultrasonic volume relaxations, proving that the \ensuremath{\alpha} relaxation of viscous liquids is responsible for the line broadening of the spectra. From the temperature dependence of the integrated area of the M\"ossbauer spectrum a second dynamic process is inferre…
The role of impurities in the irradiation induced densification of amorphous SiO(2).
2011
In a recent work (Buscarino et al 2009 Phys. Rev. B 80 094202), by studying the properties of the (29)Si hyperfine structure of the E'(γ) point defect, we have proposed a model able to describe quantitatively the densification process taking place upon electron irradiation in amorphous SiO(2) (a-SiO(2)). In particular, we have shown that it proceeds heterogeneously, through the nucleation of confined densified regions statistically dispersed into the whole volume of the material. In the present experimental investigation, by using a similar approach on a wider set of materials, we explore how this process is influenced by impurities, such as OH and Cl, typically involved in relevant concent…
New process of silicon carbide purification intended for silicon passivation
2017
Abstract In this work, we report on a new, efficient and low cost process of silicon carbide (SiC) powder purification intended to be used in photovoltaic applications. This process consists on the preparation of porous silicon carbide layers followed by a photo-thermal annealing under oxygen atmosphere and chemical treatment. The effect of etching time on impurities removal efficiency was studied. Inductively coupled plasma atomic emission spectrometry (ICP-AES) results showed that the best result was achieved for an etching time of 10 min followed by gettering at 900 °C during 1 h. SiC purity is improved from 3N (99.9771%) to 4N (99.9946%). Silicon carbide thin films were deposited onto s…
Luminescence of rutile structured crystalline silicon dioxide (stishovite)
2014
Abstract Luminescence spectrum of synthetic mono-crystalline stishovite comprises a slow blue band at ~400 nm (~3.1 eV) and a fast UV band at ~260 nm (~4.7 eV), as well as some bands in near-infrared range of spectra. The NIR luminescence of stishovite crystal, excited with lasers 532 nm, 248 nm and 193 nm as well as x-ray, possesses several sharp lines. A zero phonon line is situated at 787 nm (1.57 eV) and grows with cooling. An anti-Stokes line is located at 771 nm (1.68 eV). This line disappears with cooling. In a powder sample of stishovite created by shock waves generated by the impact of a 50-m-diameter meteorite in Arizona 50,000 years ago, the PL broad blue band is situated at 425 …
Peculiarities of photoluminescence of Al2O3 bulk and nanosize powders at low temperatures
2011
Abstract Photoluminescence has been studied in the aluminum oxide (Al2O3) bulk and nanosize powders in the 300–8 K temperature range. In both samples luminescence spectrum is characterized by presence of broad blue and red bands caused mainly by emission from the uncontrolled titanium impurity. At low temperatures luminescence intensity increases by several times and the red band obtains fine structure. The nature of the fine structure is discussed suggesting manifestation of splitting of the Ti3+ emitting level due to Jahn–Teller effect or overlapping of Ti3+ emission band with narrow lines from other emitting ions. The observed differences in low-temperature spectral features of nanopowde…
Effect of reactive ion beam etching on the photoluminescence of CdTe epitaxial layers
2008
http://link.aip.org/link/?JAPIAU/103/056108/1
3d impurities in Al: density functional results
1980
Self-consistent spin density functional calculations have been carried out for 3d transition metal impurities in aluminium. The width of the virtual level decreases as it moves away from the Fermi energy with increasing occupancy. The results are compared with recent XPS measurements.
EPR characterization of erbium in glasses and glass ceramics
2020
Electron paramagnetic resonance (EPR) is a well-established spectroscopic technique for electronic structure characterization of rare-earth ion impurities in crystalline and amorphous hosts. EPR spectra of erbium-doped glass matrices and nanocomposites can provide information about local structure variations induced by changes in chemical composition or crystallization processes. Characterization possibilities of Er3+ ions in glasses and glass ceramics including direct EPR measurements, indirect investigations via secondary paramagnetic probes, and optically detected magnetic resonance techniques are considered in this article. ----/ / /---- This is the pre-print of the following article: A…
Photochemical stabilization of linear low-density polyethylene/clay nanocomposites: Towards durable nanocomposites
2008
International audience; This article reports a study of the chemical modifications of LLDPE/nanoblend nanocomposites exposed to UV light in conditions of artificially accelerated ageing and natural weathering. Analysis by infrared spectroscopy of the chemical modifications produced by photoageing shows that the presence of an organo-clay leads to the decrease of the oxidation induction time of the polymer (LLDPE), which results in lower durability of the nanocomposites. Protection against photooxidation was tested with different kinds of UV stabilizers and with a metal deactivator. It is shown that the metal deactivator is very efficient in stabilizing the nanocomposite since it totally can…
Defect Calculations for Yttrium Aluminum Perovskite and Garnet Crystals
2000
Native and impurity point defects in both Yttrium Aluminum Perovskite and Garnet crystals are studied in the framework of the pair-potential and the shell model approximations. The calculated formation energies for native defects suggest that the antisite disorder is preferred over the Frenkel and Schottky-like disorder in both YAP and YAG. In non-stoichiometric compounds, the calculated reaction energies indicate that excess of Y2O3 or Al2O3 is, most likely, to be accommodated by the formation of antisites rather than vacancies or interstitials in the lattice. Enthalpies of the reactions for impurity (Ca2+, Mg2+, Sr2+, Ba2+, Cr3+, Fe3+, Nd3+, Si4+) incorporation into both YAP and YAG latti…