Showing papers in "Journal of Non-crystalline Solids in 1999"

Heterogeneity at the glass transition: a review

Abstract: Theoretical concepts and experimental evidence of heterogeneity in glass-forming liquids and polymers are reviewed. The main purpose is to provide an introduction to theoretical developments and recent experiments which have led to rapidly increasing knowledge. Realizing that there is no consensus in regard to the various scenarios of the glass transition starting from rather different assumptions we try to give a balanced overview although we also compare and interrelate some of the approaches. The experimental part describes recent nuclear magnetic resonance, dielectric, and optical experiments from which dynamically distinguishable subensembles can be selected thus proving the existence of a well defined dynamical heterogeneity.

Active and passive chalcogenide glass optical fibers for IR applications: a review

Abstract: Chalcogenide glass fibers based on sulfide, selenide, telluride and their rare earth doped compositions are being actively investigated worldwide. Great strides have been made in reducing optical losses using improved chemical purification techniques, but further improvements are needed in both purification and fiberization technology to attain the theoretical optical losses. Despite these problems, current single mode and multimode chalcogenide glass fibers are enabling numerous applications. Some of these applications include laser power delivery, chemical sensing, imaging, scanning near field microscopy/spectroscopy, fiber IR sources/lasers, amplifiers and optical switches. The authors assert that the research and development of chalcogenide glasses will grow in the foreseeable future, especially with respect to improvements in the optical quality of the fibers and the performance of the fibers in existing and future applications.

Electronic polarizability, optical basicity and non-linear optical properties of oxide glasses

Abstract: The average electronic polarizability of the oxide ion αO2−(no) of numerous binary oxide glasses (phosphate, borate, silicate, germanate, tellurite and titanate) has been estimated on the basis of the refractive index reported in literature. An optical basicity scale has been proposed on the basis of a good agreement between calculated theoretical optical basicity Λth and refractive index based optical basicity Λ(no) of the glasses. It was established that third-order non-linear optical susceptibility χ(3) of the glasses, also found in the literature, increases with increasing optical basicity and tendency for metallization of the glasses. This is associated with the high electron donor ability of the oxide ions and the small optical band gap. Conventional oxide glasses with low refractive index possess low polarizability, low optical basicity, large metallization criterion and small χ(3). Tellurite and titanate glasses as well as borate glasses containing a large amount of Sb2O3 and Bi2O3 with high refractive index above 2.0 show large polarizability, high optical basicity, small metallization criterion and large χ(3).

Optical transitions of rare earth ions for amplifiers: how the local structure works in glass

Abstract: Several properties of 4f optical transitions of rare earth ions in glasses utilized as optical amplifiers for telecommunications are discussed. For the Er 3+ : 1.55 μm transition, the role of Judd–Ofelt Ω 6 parameters is presented. With compositional change in structure of aluminosilicate glasses, the changes of the radiative cross section, quantum efficiency, and flatness, is observed, which are especially important for the amplifiers in the wavelength-division-multiplexing (WDM) network system. Moreover, the energy level structures and resultant spectral properties of Pr 3+ , Nd 3+ and Dy 3+ ions, all of which are 1.3 μm-active ions, are compared. The hypersensitivity of Dy 3+ transitions appears especially in chalcogenide glasses, where the non-radiative loss due to multiphonon emissions is minimized. Compositional variations of the branching ratio and radiative cross sections, and their dependence on the Ω 2 parameters, which are affected by the asymmetry of the rare earth ion sites, are discussed.

Non-linear optical properties of chalcogenide glasses in the system As S Se

Abstract: We report results of a systematic study examining the relationship of bond type and concentration to the linear and non-linear optical properties of As–S–Se glasses. The effects of iso-structural substitution of Se for S and the resulting impact on structure and the non-linear refractive index, n 2 , are discussed. Non-linear optical properties of As–S–Se chalcogenide glasses were measured by the Z-scan technique at 1.6 μm, and measured n 2 up to 400 times the n 2 for silica were observed. Such large n 2 for glasses with small As/(S + Se) molar ratios is correlated with the presence of covalent, homopolar Se–Se bonds in the glass structure as identified by Raman spectroscopy, and can not be attributed to any red shift in the absorption edge or to a resonant effect. The suitability of these glasses for planar waveguides based on such nonlinear properties is thus confirmed, and recent fabrication results are described.

Determination of the sp3/sp2 ratio of a-C:H by XPS and XAES

Abstract: X-ray photoelectron spectroscopy and X-ray excited Auger electron spectroscopy were used to determine some of the properties of diamond like amorphous carbon films deposited using saddle field glow discharge of methane. By applying the chemical shift technique and curve fitting technique to the C1s peak in the X-ray photoelectron spectrum of the film, we were able to determine the sp 3 /sp 2 bonding ratio of the films. The ratio from this method was in agreement (±1%) with that calculated from the X-ray excited Auger electron spectrum of the same film. The method was also applied to a-C:H films doped with different impurities (boron and phosphorus) in amounts varying from 1% to 20%. We found that the sp 3 /sp 2 ratio of the film was dependent on the deposition parameters and on types of impurities and their concentrations.

Spectral properties of carbon black

Abstract: The internal structure of carbon black particles considerably influences the optical behavior of the material, apart from the shape and agglomeration state of the primary particles. In this paper the correlation between internal structure and spectral behavior of carbon black is investigated experimentally. The carbon blacks were produced by resistive heating of graphite electrodes and condensation in a cooling gas atmosphere. The internal structure of the primary carbon black particles was investigated by high-resolution transmission electron microscopy, electron energy loss spectroscopy, 13 C NMR spectroscopy, and Raman spectroscopy. The primary particles were found to consist of bent or plane structural subunits. The UV π−π* absorption feature of the produced carbon blacks varies in position between 196 and 265 nm depending on the state of bending of the graphene layers in the subunits of particles and/or the dimensions of the plane graphitic microcrystallites and the incorporation of hydrogen. The different curvature radii of the graphene layers or the sizes of microcrystallites can be summarized by an integral dimension like the ratio of sp2/sp3 hybridized carbon atoms. In the mid-infrared spectral region, the absolute value of the absorption coefficient κ is dominated by a continuous absorption due to free charge carriers which are also influenced by the ratio of sp2/sp3 hybridized carbon in the primary particles. The appearance of prominent bands is related to the existence of functional groups, like C–Hn, CO and/or C–O–C.

FTIR and XPS studies of P2O5-Na2O-CuO glasses

Abstract: The short range structure of ternary sodium–copper–phosphate [(40–70)P2O5–(0–60)Na2O–(0–50)CuO (mol%)] samples were examined by Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The XPS O 1s spectrum was deconvoluted into three components, symmetric bridging oxygen (P–O–P), non-bridging oxygen ( and PO) and asymmetric bridging oxygen (P–O–Cu). In the ultraphosphate and metaphosphate glasses, the P–O–Cu bonds are formed replacing bonds while keeping the same fraction of P–O–P bonds as Na2O is replaced by CuO. Whereas, in the polyphosphate glasses, the formation of P–O–Cu will replace both P–O–P and bonds. The results reveal the formation of P–O–Cu bonds in these glasses, and an increase of crosslink density. Thus, chemical durability and Tg of the glasses are increased.

Solid state 27Al NMR and FTIR study of lanthanum aluminosilicate glasses

Abstract: The structure of lanthanum aluminosilicate (LAS) glasses, containing: (15–25) mol% La2O3, (15–35) mol% Al2O3 and (40–70) mol% SiO2, were studied by 27Al nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The effects of La2O3 and Al2O3 content on the properties and structure of the LAS glasses were evaluated. Al3+ ion enters into the glass structure mainly in fourfold co-ordination, forming ( AlO 4/2 ) − tetrahedra, and only in small amounts in fivefold and sixfold co-ordination. La3+ acts as network modifier, producing more non-bridging oxygen atoms as its content increases.

Effect of melting temperature and time on iron valence and crystallization of iron phosphate glasses

Abstract: The effect of melting temperature and time on iron valence, dissolution rate (DR) in deionized water, and crystallization of iron phosphate glasses was investigated using a 40Fe2O3–60P2O5, mol%, batch composition. The concentration of Fe2+ ions in these glasses increased from 17% to 57% as melting temperature increased from 1150°C to 1450°C, but remained nearly constant at about 20% for melting times longer than 1 h at 1200°C. Measurements by differential thermal analysis (DTA) combined with X-ray diffraction (XRD) and thermogravimetric analysis (TGA) showed that these glasses crystallized to Fe3(P2O7)2 and Fe4(P2O7)3 when heated in nitrogen between 600°C and 820°C, but with continued heating in air at 820°C the Fe3(P2O7)2 changed to Fe(PO4), which produced a weight gain in the sample associated with the oxidation of Fe2+ to Fe3+ ions. The DR (in deionized water) of these glasses was generally very low (∼10−9 g cm−2 min−1) and nearly independent of the relative concentration of Fe2+ or Fe3+ ions, but decreased with total iron content.

Thermodynamic properties of Pd-based glass-forming alloys

Abstract: Undercooled liquids of the easy glass-forming alloys Pd–Ni–P and Pd–Cu–Ni–P (Pd40Ni40P20, Pd40Ni10Cu30P20, Pd43Ni10Cu27P20) have an extra-ordinary stability against crystallization allowing for direct calorimetric measurements of this metastable state. The liquid alloys can be undercooled consistently into the glassy state at moderate cooling rates of about 0.2 K/s and heat capacity measurements have been performed covering the undercooling regime from the melting temperature to the glass transition temperature. The thermodynamic functions of the alloys in dependence on temperature were evaluated. The isentropic temperature, TK, often interpreted as the low temperature limit of the liquid state, was determined from the excess entropy. Enthalpy relaxation experiments show that the addition of Cu leads to an increase in the fragility of the Pd-based alloys.

Enhanced fluorescence from Eu3+ owing to surface plasma oscillation of silver particles in glass

Abstract: We describe the increase of europium ion (Eu3+) fluorescence owing to resonant plasma oscillation of silver (Ag) particles in silica (SiO2) glass, which were precipitated by annealing in a reducing atmosphere sol–gel derived SiO2 glass containing Ag+ and Eu3+ ions. Nanometer size effects of Ag particles on the increase were also investigated as a function of the reduction time. The mean particle size and the volume fraction of silver particles in glass were estimated from absorption spectra using the Mie–Drude theory modified by the electron mean free path model. The fluorescence from Eu3+ ions when the excitation was a N2 laser increased in the presence of silver particles of ∼4.3 nm size. From comparison of the radiative damping time of the plasma oscillation with the lifetime of Eu3+ fluorescence we, tentatively, concluded that the induced surface plasma oscillation by incidence and the interaction between Eu3+ and Ag particles occurred simultaneously.

What do electrical conductivity and electrical modulus spectra tell us about the mechanisms of ion transport processes in melts, glasses, and crystals?

Abstract: The significance of electrical conductivity and electrical modulus spectra with respect to ion transport mechanisms in melts, glasses, and crystals is discussed. It is shown that in the typical frequency range of an ac impedance experiment, the real part of the conductivity, σ′, is exclusively determined by the ion transport dynamics, while the imaginary part of the modulus, M″, is additionally influenced by vibrational and electronic polarisations. Accordingly, conclusions from the shape of M″ spectra about ion transport mechanisms cannot be drawn without properly taking into account the influence of these polarisations. Generally, it can be argued that analyses in terms of conductivity or dielectric spectra are preferable to analyses in terms of modulus or resistivity spectra if the electrical properties of a sample can be represented by resistances acting in parallel.

Brittleness of glass

Abstract: A study seeking to decrease the brittleness of glasses was carried out. The brittleness, defined as the ratio of hardness to fracture toughness, was estimated from the ratio of median crack length to the diagonal length of a deformation impression. The brittleness of various kinds of glasses in the silicate as well as borosilicate systems was investigated as a function of glass properties. The brittleness of the glasses was correlated with densities, i.e., a variation of ∼1 to ∼9 μm−1/2 in brittleness was observed as the density varied from ∼1.9 to ∼2.8 g/cm3. The brittleness of normal glasses decreased with decreasing density due to the ease of both plastic flow and densification. On the other hand, the brittleness of anomalous glasses increased with decreasing density due to the lack of plastic flow. In addition, the brittleness of normal glasses was less than that of the anomalous glasses with the same density. We also observed that a 50% decrease in brittleness resulted in an increase of crack initiation load by ∼15 times.

Part 2.125Te NMR study of M2O–TeO2 (M=Li, Na, K, Rb and Cs) glasses

Abstract: The structure of TeO2 and M2O–TeO2 (M=Li, Na, K, Rb and Cs) glasses has been investigated by means of 125Te static and magic-angle spinning (MAS) NMR spectroscopies. On the basis of the relationship between the local structures around Te atoms and the NMR parameters obtained by 125Te NMR spectra of various tellurite crystals, the local structures around Te atoms in TeO2 and M2O–TeO2 glasses were examined. The spectral simulation of static NMR spectra enabled us to discriminate between TeO3 trigonal pyramid (tp) and TeO4 trigonal bipyramid (tbp) and to estimate the fractions of TeO3 tp (N3) and TeO4 tbp (N4). It was concluded that in TeO2 glass TeO4 tbps are connected by sharing their corners as in α-TeO2 crystal. N3 increased and N4 decreased with increasing M2O content. On the basis of a previous structural model, the fractions of TeO4 tbp without a non-bridging oxygen (NBO) atom, TeO4 tbp with an NBO atom, and TeO3 tp with two NBO atoms were calculated. A new model which presents the structural change for M2O–TeO2 glasses has been proposed.

Microwave properties of zinc, barium and lead borosilicate glasses

Abstract: The trend to fabricate mulitlayer structures of microwave dielectric ceramics cofired with low melting conductors results in the demand of additives for low temperature sintering. Low-melting glasses are good candidates for low temperature sintering aids. When the concentration of the added low-melting glasses reaches a high content of about 10–20 mol%, their microwave properties will certainly affect the performance of the final multilayer devices. It is the object of this study to investigate the microwave properties of low-melting ZnO–B 2 O 3 –SiO 2 , BaO–B 2 O 3 –SiO 2 , and PbO–B 2 O 3 –SiO 2 glasses. The parallel plate dielectric resonator rod method was employed for measurements of relative dielectric constants, quality factors, and temperature coefficients of frequency in the microwave frequency range. A thermo-mechanical analyzer was used to determine deformation temperatures of glasses. Properties of these three glass systems are chiefly determined by the amount of structural modifier oxides (ZnO, BaO, and PbO) and the ionic size of the modifying cations (Zn 2+ , Ba 2+ , Pb 2+ ). In contrast, the effect of the ratio of B 2 O 3 to SiO 2 is relatively small. The frequency constants of these three glass systems range from 500 to 3400, which are equivalent to tan δ of 0.02–0.003 at 10 GHz. The temperature coefficients of frequency range from −3 to −155 ppm/°C.

Factors affecting molecular dynamics simulated vitreous silica structures

Abstract: To obtain accurate results in molecular dynamic (MD) simulations of glasses, it is essential to chose proper force fields (FF), proper length of the simulation cell, and proper cooling cycle to generate 300 K structures from liquid. Herein we establish guidelines for these choices. We find that the MS-Q force field (FF) and the Molecular Simulations Incorporated (MSI) glass FF both lead to agreement with the radial distribution function (RDF) from small angle neutron scattering (SANS) experiments. We find that the simulation cell should contain about 3000 atoms to obtain run to run density variation less than 1% and consistency in the first two RDF peaks of 0.001 nm. A cell of 648 atoms gives run to run density variation of up to 5% and consistency in the first three RDF peaks of 0.001 nm. We find that a good compromise between accuracy and reproducibility of results and simulation time is to start with NVT dynamics at 8000 K followed by cooling to room temperature at a rate of 100 K/2 ps.

Rare-earth doped transparent glass-ceramics with high cross-sections

Abstract: Erbium doped oxy-fluoride glass-ceramics (50GeO2,[50−x]PbO,xPbF2) have been prepared by thermal treatments of as-melted glass. The optical absorption and emission cross-sections were measured. The controlled crystallisation of the fluoride compounds by nucleation and growth in the oxide matrix produced crystallites ∼10 nm in size and a filling factor of 10−2. The phase separation process was investigated using thermal and structural analysis. Changes were observed in the optical properties of the glass after reheating (10 h at 360°C). The inhomogeneous linewidth of the 4I15/2↔4S3/2 transition was reduced by 50% by incorporating most of the Er ions in the crystalline phase. An increase of the maximum absorption cross-section, up to 100%, was obtained at room temperature.

A catalyst-free approach for sol–gel synthesis of highly mixed ZrO2–SiO2 oxides

Abstract: The synthesis of mixed ZrO2–SiO2 oxides has been carried out using a new non-acid–base alkoxide route. The chemical reactivity of zirconium n-propoxide (ZP) is first modified with the chelating agent acetylacetone (acac) before it is brought in contact with tetraethoxysilane (TEOS). It is found that the gelation rate of bi-component sols is much faster than those of the mono-components under similar preparation conditions. A self-catalytic effect of the resultant Zr–O–Si on Si–O–Si formation is thus identified. By employing FTIR/DTA/TGA/XRD techniques, the mixing level of the two oxides in terms of Zr–O–Si hetero-linkages has been investigated in detail. A linear relationship between the IR absorption band shift of Zr–O–Si linkages and the Zr content is established to indicate the amount of oxide mixing. Phase segregation and thermal decomposition of xerogels upon calcination are studied and factors responsible for good mixing are also discussed. Using this approach, a high level of mixing has been achieved for the ZrO2–SiO2 binary oxides (Zr up to 50 mol%) with an acac to ZP molar ratio in the range 0.2–0.4 in the absence of an acid or base catalyst.

Towards a theory for the mixed alkali effect in glasses

Abstract: A general theoretical approach for the mixed alkali effect in glasses is discussed based on the idea that the covalent host network creates different structural energy landscapes for different types of mobile ions. By deriving a simplified model from this approach, it is shown how the experimentally observed changes in ion mobilities both upon mixing of two types of ions and upon changing the total concentration of mobile ions can be understood. Computer simulations of the model suggest that Coulomb forces have to be taken into account for explaining the differing behavior of activation energies in single modified and mixed ion glasses. It is further shown how the mixed alkali internal friction peak results from diffusional exchange processes of unlike ions in the glassy network.

Bioaccumulation of some hazardous metals by sol–gel entrapped microorganisms

Abstract: This paper reports immobilization of baker's yeast cells (saccharomyces cerevisiae) by entrapment of the biomass in a sol–gel matrix. The solid biogel was observed to accumulate hazardous heavy metals from aqueous solutions. The metal uptake capacity of the biogels was essentially the same as that of the free yeast cells for Hg(II) and Cd(II). However, free yeast cells showed better bioaccumulation capacity for Pb(II) and Cu(II) while a lower capacity was observed in the cases of Co(II), Ni(II), and Zn(II). The siloxane based sol–gel entrapment matrix positively contributes to the overall metal uptake of the biogel, which was observed to contain intact yeast cells homogeneously distributed into the solid matrix. The affinity of the biogel for metal ion bioaccumulation followed the order Hg(II) > Zn(II) > Pb(II) > Cd(II) > Co(II) ≅ Ni(II) > Cu(II). Metal uptake characteristics of the biogel also depend on pH, buffer type and temperature.

Vibrational spectra, related properties, and structure of inorganic glasses

Abstract: Methods for the quantitative analysis of the IR and Raman spectra of various inorganic glasses to determine physically meaningful optical functions and individual band parameters are discussed. Available approaches to the problem of how to describe the mechanism of formation of the vibrational spectra of glasses (such as the quasi-molecular model, central force model and its recent refinements, and the model of phonon localization regions) are critically discussed. Recent data on band intensities and/or frequencies obtained with these methods for phosphate, borate, and germanate glasses are considered. Trends in the IR and Raman band assignments deduced from the current state of vibrational spectroscopy of glasses are analyzed and structural information obtained by different authors for binary phosphate, borate, and germanate glasses is compared. It is shown that, based on data on individual band parameters obtained, some related optical and dielectric properties of glasses in their transparency range can be calculated and/or modeled. Particular directions that are promising for further development of studies into vibrational spectroscopy of glasses are specified.

Photoinduced changes in the linear and non-linear optical properties of chalcogenide glasses

Abstract: The linear refractive index, n, and the position of the absorption edge for thin chalcogenide/chalcohalide films from the systems As–S, As–S–X (X=Bi, Tl or I), and Ge–S–Me (Me=Bi, Tl, As) have been measured before and after exposure to above-bandgap illumination. For compositions containing either As or Ge, the absorption edge was shifted to longer wavelengths (i.e. photodarkening occurred) for As-containing films, and to shorter wavelengths (i.e. photobleaching occurred) for Ge-containing films. As–S–Ge films exhibit either photodarkening or photobleaching, depending on Ge content. The largest values of these edge shifts ranged from 20 up to 60 nm, in the case of Ge31S63Tl6. The conditions for synthesizing the glasses studied are reported. A formula for predicting the non-linear refractive index, n2, for chalcogenide/chalcohalide glasses from the dispersion of n, and which enables n2 to be related to structural parameters, has been developed and compared with existing formulae for other types of glass and crystals. Using the various formulae and the measured values of n, n2 for these materials has been predicted. The results indicate that glasses with compositions near As42S58 or As2S3Tl0.13 may, after UV exposure, exhibit significantly larger values of n2 than as-deposited As40S60.

Calcium phosphate invert glasses with soda and titania

Abstract: Calcium phosphate glasses in the pyrophosphate region were obtained by addition of Na2O and TiO2. The glasses with CaO content of ⩾55 mol% contain pyrophosphate and orthophosphate groups without metaphosphate by Raman and NMR observation. Crystalline phases with bioactivity such as β-Ca3(PO4)2 and/or β-Ca2P2O7 were precipitated in the glasses at 850°C. Some of the glasses can be sintered at 850°C, resulting in glass-ceramics containing significant amounts of bioactive phases.

Effect of relative alkali content on absorption linewidth in erbium-doped tellurite glasses

Abstract: Er 3+ doped tellurite glasses with various Na 2 O/Li 2 O, Na 2 O/K 2 O and K 2 O/Li 2 O ratios (0-4.5) were prepared at 850°C using a platinum crucible. The effect of relative alkali content on absorption linewidth in erbium-doped tellurite glasses was investigated. The highest effective linewidth was obtained from glass samples with mixed alkali molar ratio of Na 2 O/Li 2 O=1, Na 2 O/K 2 O=1 and K 2 O/Li 2 O=1. Glass transition temperature, crystallization temperature, density, refractive index, Judd-Ofelt parameters and emission cross-section of Er 3+ doped tellurite glasses are also reported.

Formation of LaF3 microcrystals in sol–gel silica

Abstract: A novel sol–gel process for silica/fluoride composites is described. Crystallization of LaF3 in the sol–gel silica has been investigated. Dry silica gels containing La3+ and trifluoroacetate ions (CF3COO−) were produced from tetramethylorthosilicate (TMOS), methanol, dimethylformamide, lanthanum acetate, trifluoroacetic acid, water and nitric acid. By heating the gels at temperatures above 300°C, LaF3 microcrystals with a size of 10–30 nm were formed in the silica matrix. IR, XPS and TG-DTA analyses suggested that CF3COO− ions are coordinated to La3+ ions in the sols and the dried gels, leading to the formation of LaF3 by the thermal decomposition at elevated temperatures.

Cation clustering and formation of free oxide ions in sodium and potassium lanthanum silicate glasses: nuclear magnetic resonance and Raman spectroscopic findings

Abstract: Alkali silicate glasses containing lanthanum oxide are useful model systems for understanding the structural role of rare earth cations in optical and other types of materials. We report 29 Si and Raman spectra of sodium and potassium silicate glasses, both with added La 2 O 3 and with La 2 O 3 substituted for Na 2 O or K 2 O on an equal-oxygen basis. In the former series, silicate speciation changes show the formation of more non-bridging oxygens (NBO) as more of the network-modifying La 2 O 3 is added. In the latter series, however, in which the nominal ratio of NBO to Si is constant, silicate speciation changes indicate that the actual ratio decreases significantly as La is substituted for 3 Na or K. The simplest explanation of this finding is that up to several percent of the oxygen in the La-rich glasses is not bonded to any Si, but instead forms `free oxide' ions that are part of La-rich domains. Although the size of these domains remains unconstrained, the lack of evidence for phase separation and continuity of trends in structure with composition suggests that the metastable liquid structure at the glass transition contains substantial intermediate-range heterogeneity.

Synthesis of silver clusters in silica-based glasses for optoelectronics applications

Abstract: The techniques of silver–sodium ion exchange and Ag + ion implantation in glass have been successfully applied for producing silver clusters in soda-lime glass optical waveguides. Optical absorption spectroscopy, time and spectrally resolved photoluminescence, Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy and transmission electron microscopy measurements were made. Structural changes of the Ag + environment were observed in ion-exchanged samples prepared in liquids with different Ag + concentrations. Heat treatments in air and in H 2 atmospheres induced cluster formation in ion-exchanged samples through different reduction–migration mechanisms, whereas clusters formation in ion-implanted samples is related to the defect concentrations induced by the radiation damage.

Silicon oxycarbide glasses from silicone networks

Abstract: Rubbers resulting from the hydrosilylation reaction between poly(methylsiloxane), and 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcycletetrasiloxane, have been pyrolyzed to silicon oxycarbide ceramics, with ceramic yield varying as a function of the mixture composition. The rubber–ceramic conversion process was investigated by 13C and 29Si nuclear magnetic resonance and infrared spectroscopies, thermogravimetric analysis and density measurements. The composition of the ceramic products was determined by elemental and X-ray fluorescence analyses and their structural characterization was done by 29Si solid-state magic angle spinning nuclear magnetic resonance. The structure of the ceramic products is, actually, a mixture of SiO4, SiCO3, SiC2O2, SiC3O, SiC4 sites randomly distributed in the bulk. The C–C/SiCxO4−x composites were prepared by infiltration of the siloxane mixture into the bidirectionally reinforced carbon plate. The composites obtained after pyrolysis showed an improved resistance to oxidation in relation to untreated carbon plates.

Optical and surface properties of inorganic and hybrid organic–inorganic silica–titania sol–gel planar waveguides

Abstract: Inorganic and hybrid organic–inorganic silica (SiO2)–titania (TiO2) planar waveguides, with a relative molar composition 70–30, have been fabricated by sol–gel dip-coating. The composition and the density of the film samples have been measured by Rutherford backscattering spectrometry, nuclear reaction analysis and elastic recoil detection analysis. The measured compositions have been found to agree with the nominal composition of the sols. The film density of the inorganic samples increased with the firing temperature in the range 1.80–2.58. A root mean square roughness (rms) <1 nm was measured on the surface of the samples by atomic force microscopy. A refractive index in the range 1.61–1.54 was measured (λ=632.8 nm). The inorganic waveguides had smaller losses (∼0.3 dB cm−1) compared to the hybrid waveguides (∼1 dB cm−1).