Search results for "Amorphous solid"

Über die intensitätsabhängigkeit der ultrarotbanden von der temperatur und vom kristallisationsgrad

1961

Beim Erhitzen von Polyathylenen und Paraffin geben die amorphen Banden bei 7,68μ und 7,38μ die Abnahme des Kristallisationsgrades richtig wieder, die kristalline Bande bei 13,7μ zeigt dagegen eine uber das partielle Schmelzen hinausgehende, durch Torsionsschwingungen der Ketten im Kristallgitter bedingte Intensitatsabnahme. Beim Terylen zeigen alle von uns untersuchten kristallinen und amorphen Banden eine verschiedene Abhangigkeit von der Temperaturbewegung, wobei einige amorphe Banden beim Erhitzen sogar verschwinden. Bei Messungen bei konstanter Temperatur zeigen alle Banden im Verlauf einer Kristallisation eine ubereinstimmende Veranderung mit zunehmendem Kristallisationsgrad. At the he…

1979

2D NMR spectra have been measured at variable temperatures between −100°C and +110°C in a sample of melt crystallized deuterated polyethylene (PE). The line shape could be decomposed into a central part originating from deuterons in the amorphous regions and outer parts from crystalline regions of PE. The “NMR crystallinity” determined from this separation was 72% in agreement with the X-ray crystallinity of 74%. Changes of the crystalline NMR line shape were interperted in terms of oscillations around the chain axis, the r.m.s. oscillation amplitude varying from 5° at 40°C to 12° at 110°C. The central part of the NMR line shape indicates the existence of a “narrow” and a “medium” component…

Vacuum-ultraviolet absorption of hydrogenated and deuterated silanol groups and interstitial water molecules in amorphousSiO2

2005

Vacuum-ultraviolet (VUV) absorption cross sections of hydrogenated and deuterated silanol groups (SiOX, where $\mathrm{X}=\mathrm{H}$ or D) as well as interstitial water molecules $({\mathrm{X}}_{2}\mathrm{O})$ in amorphous $\mathrm{Si}{\mathrm{O}}_{2}$ $(a\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2})$ were determined between photon energies of 7 and $8.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The absorption bands for the deuterated species are blueshifted compared to those for the hydrogenated ones by $\ensuremath{\sim}0.1\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}0.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ as a result of a decrease in the zero-point energy associat…

INFLUENCE OF THE ANODIZATION CONDITIONS ON THE ELECTRONIC PROPERTIES AND CRYSTALLOGRAPHIC STRUCTURES OF THE CORROSION LAYERS ON TUNGSTEN. A PHOTOELEC…

1983

ABSTRACT The influence of morphology, composition and crystallographic structure on the photoelectrochemical behaviour of anodic oxide films on tungsten obtained in various conditions of anodization has been investigated. Different photocurrent spectra and absorption edges were obtained for each type of film. Optical band gaps ranging between 2.55 eV and 3.15 eV were determined for crystalline and amorphous WO 3 films grown in different conditions. The low quantum efficiency of the anodic films must be attributed to the presence of an amorphous (a-W0 3 ) film which controls the transport of the injected photocarriers.

1986

The molecular order and mobility of two liquid-crystalline polyacrylates with phenyl benzoate moieties as mesogenic side groups and (CH2)m spacers (m = 2 and m = 6) were investigated by pulsed 2H NMR. The mesogenic side groups were isotopically labelled at the terminal phenylene ring. In the glassy state the orientational distribution function was characterized from the angular dependence of the 2H NMR line shape of samples macroscopically ordered in their nematic phase by the 8,4 T magnetic field of an NMR spectrometer. It was found to be Gaussian with widths of ± 18,5° and ± 10,5° for the m = 2 frozen nematic and m = 6 frozen smectic system, respectively. The phenylene rings undergo 180° …

Amorphous Ge15Te85: density functional, high-energy x-ray and neutron diffraction study

2011

The structure and electronic properties of amorphous Ge15Te85 have been studied by combining density functional (DF) simulations with high-energy x-ray and neutron diffraction measurements. Three models with 560 atoms have been constructed using reverse Monte Carlo methods constrained to (1) agree with the experimental structure factors S(Q), and have (2) energies close to the DF minimum and (3) a semiconducting band structure. The best structure is based on the melt-quenched DF structure and has a small number of Ge–Ge bonds. It shows interlocking networks of Te and GeTe with a significant fraction (22–24%) of voids (cavities). Ge occurs with both tetrahedral and 3 + 3 defective octahedral…

15N NMR studies of tautomerism

2012

The literature related to 15N NMR studies of tautomerism is updated and discussed. The 15N NMR data show that the technique is applicable for both liquid and solid state (both crystalline and amorphous) materials. Modern computational methods combined with experimental NMR data can aid in the chemical shift assignments especially in case of crystalline materials (so-called NMR crystallography). This review article is divided into chapters based on the different classes of compounds and a brief description of experimental and computational NMR techniques is also included.

Room Temperature Instability of E′γ Centers Induced by γ Irradiation in Amorphous SiO2

2008

We study by optical absorption measurements the stability of E'(gamma) centers induced in amorphous silica at room temperature by gamma irradiation up to 79 kGy. A significant portion of the defects spontaneously decay after the end of irradiation, thus allowing the partial recovery of the transparency loss initially induced by irradiation. The decay kinetics observed after gamma irradiation with a 0.6 kGy dose closely resembles that measured after exposure to 2000 pulses of pulsed ultraviolet (4.7 eV) laser light of 40 mJ/cm(2) energy density per pulse. In this regime, annealing is ascribed to the reaction of the induced E'(gamma) centers with diffusing H(2) of radiolytic origin. At higher…

XAFS STUDIES OF OCTAHEDRAL AMORPHOUS OXIDES

1993

The relationships between the structures of octahedral and tetrahedral amorphous oxides, studied by XAFS spectroscopy, are considered. It was found that a-WO3, a-MoO3, a-V2O5 thin films and glasses have strongly distorted, but well defined, oxygen octahedra, which are joined by vertices (a-WO3, a-MoO3) or by vertices and edges (a-V2O5), and form a random network. At the same time, a-IrO2 and a-NiO have less distorted oxygen octahedra, which form the rutile type and rock salt type nanocrystalline structures. The variation of the structure with the change of the metal valence is considered and the possibility of small radius polaron detection by XAFS is discussed.

Grain-size-induced relaxor properties in nanocrystalline perovskite films

2004

Thin films of ${\mathrm{Pb}}_{0.76}{\mathrm{Ca}}_{0.24}{\mathrm{TiO}}_{3}$ (PTC), which is a classical ferroelectric as a bulk material and of the relaxor material $\mathrm{Pb}({\mathrm{Sc}}_{0.5}{\mathrm{Nb}}_{0.5}){\mathrm{O}}_{3}$, have been produced to find out whether nanocrystalline ferroelectric films show a grain-size-induced relaxor behavior. Amorphous films were deposited onto a $\mathrm{Ti}∕\mathrm{Pt}$ coated silicon (100) wafer by reactive $\text{rf}$ sputtering. Different grain sizes were prepared by a controlled annealing process and they were determined by profile analysis of x-ray diffraction spectra. Temperature dependent Raman spectroscopy was used to look for phase trans…