Browsing by Author "Nofz, Marianne"

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    Effects of phase Separation and devitrification processes in oxide glasses on ESR spectra
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Nofz, Marianne; Stösser, Reinhard; Scholz, Gudrun
    The consequences of phase Separation and devitrification processes for the ESR patterns of Fe³⁺ ions and oxygen hole centres in giassy and glassy-crystalline Systems are discussed. Analysis of the Fe³⁺ spectra by Simulation (including 4th order terms) allows their model-based Interpretation for homogeneous, phase-separated and devitrified samples as well. It is even possible to estimate the ratio of Fe³⁺ ions incorporated into the giassy matrix to those localized in the crystalline phase. An influence of irreversible structural reorganization in glasses on γ-irradiation-induced oxygen hole centres is detectable by studying their Saturation behaviour For the example of a barium Silicate glass studied here, pronounced passage effects could be detected at 77 K. In contrast, a devitrified sample of the same composition after γ Irradiation yielded the same spectral pattern at low microwave power, but only Saturation broadening was to be observed when rising the microwave power. In an annealed sample of anorthite composition (in mol%: 25CaO, 25AI₂O₃, 50SiO₂) progressive crystal growth was detectable using Fe³⁺ ions as probes.
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    ESR spectroscopic study on the incorporation of Fe(III) into Li2O-Al2O3-B2O3 glasses
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Nofz, Marianne; Hähnert, Manfred; Stößer, Reinhard
    The X band ESR spectra at 77 and 300 K of Li2O—Al2O3—B2O3 glasses investigated comprize four resonances, which can be assigned to Fe3+ ions brought into the samples by the raw materials, mainly by alumina. Signals at g' = 3, 2.3, 2.07 are due to Fe3+ ions incorporated into an autonomous FexOy phase or respective cluster-like precursors. The amplitude of the g' ≈ 4.3 signal typical for the Fe3+ ion in oxidic glasses corresponds with the Li2O content of the glasses. This indicates that the Fe(III)/∑ Fe ratio is mainly influenced by the ability of the Li+ ion to stabilize [FeO4/2]- , i.e., four-fold coordinated Fe(III) can only be stabilized if the Li+ content of the glasses is sufficiently large.
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    ESR spectroscopy on glasses and glassy-crystalline materials - New opportunities for material scientists
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Stößer, Reinhard; Nofz, Marianne
    Analyzing the state of the art of ESR applied to glasses, one can state that all results obtained so far give evidence for the fact that the electron (and nuclear) spin properties are related in a unique manner to the local properties of glassy systems. Therefore, all spin-derived experimental parameters obtained for non-crystalline solids are dispersed around mean values. Suitable theoretical models for an adequate representation of the complex ESR spectra of glasses are reviewed and critically analyzed. The information about the glassy state of matter generated with the help of paramagnetic species offers new opportunities for material sciendsts: criteria for the homogeneity, devitrification and crystallizadon of glasses on a microscopic level; indication of redox processes; localization and function of dopants and their effect on the material properties; evidence for different kinds of internal strain. Some relevant, up to now not commonly used methodical ESR developments like in-situ bending stress experiments, tomography, wide range (4 K ≤ T ≤ 1000 K ) temperature dependence are presented.
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    IR and Raman spectroscopic study of some strontium aluminosilicate glasses
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Peuker, Christel; Brzezinka, Klaus-Werner; Nofz, Marianne; Pilz, Walter; Geißler, Heinz
    Vibrational spectra are measured for strontium aluminosilicate glasses with the composition (in mol%) x SrO ∙ y AI2O3 ∙ (100-x-y) SiO2 (33 ≤ x ≤ 40, 0 ≤ y ≤ 2) with a water content ranging from 0.014 to 0.14 mol ∙ l-1 . The OH bands systematically change with glass composition in both MIR and NIR regions. The ratio of the absorption coefficients α3550/α2800 increases with decreasing number of nonbridging oxygens per tetrahedron (NBO/T; Τ = Si, AI). This indicates an increasing amount of strongly hydrogen bonded OH groups (2800 cm-1) with NBO/T relative to the weakly bonded hydroxyls (3550 cm-1) within the compositional series. Intensity changes in the Raman and IR reflectance spectra also reflect the substitution of Al3+ for Si4+ in the network and the incorporation of Sr2+. The increasing intensity ratio of the Raman bands I945/I1070 with NBO/T indicates an increase of structural units relative to Q^3, as well as the weak shoulder at 870 cm-1 shows a rising amount of Q units. The growing intensity of the IR reflectance band at 930 cm-1 with NBO/T confirms the increasing amount of nonbridging oxygen in the glasses. A depolarized Raman band at 330 cm-1 was assigned to an Sr-O vibration. For hydrated samples the significantly higher ratio of α3550/α2800 in relation to the basic glasses can be explained by structural changes in the samples due to the water enrichment procedure. The hydroxyl content of the basic and hydrated glasses can be estimated by the so called two-band method with composition independent extinction coefficients for the two IR bands at about 3550 and 2800 cm-1, ε3550 = 80 1 ∙ mol-1 ∙ cm-1 and ε2800 = 170 1 ∙ mol-1 ∙ cm-1, independent of the Al3+ content of the glasses.
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    On the interaction of glasses with high-energy radiation - Combined ESR and optical studies
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Nofz, Marianne; Reich, Christian; Stösser, Reinhard; Bartoll, Jens; Janata, Eberhard
    This paper will discuss some aspects of the induced physical processes and chemical reactions which are observed when Silicate and aluminosilicate glasses are exposed to UV radiation (248 nm; excimer laser), γ radiation (⁶⁰Co) and pulses of fast electrons (3.8 MeV). The stimulated emission and absorption of short-lived defects and Čerenkov radiation are detected in the optical ränge between 200 and 800 nm and on the microsecond time scale. Stahle hole centres (Si-0⁻/h⁺, Si-O-Al/h⁺) and electron centres (among others Zn⁺, Cd⁺, (Fe³⁺)⁻) are detected by ESR spectroscopy at room temperature. They show surprising differences in regard to their thermal stability, i.e., the distribution and mean value of their trap depths. Induced absorption in the UV/VIS range exhibits broad and overlapping bands, some of which can be partially assigned to centres detected by ESR spectroscopy. Therefore, UV/VIS spectroscopy provides complementary information, an induced absorption at 300 nm for example, which has no analogy in ESR measurements.