Nonlinear optical studies of lead lanthanum borate glass doped with Au nanoparticles

Synthesis, characterization and optical nonlinearity of lead lanthanum borate glass embedded with gold nanoparticles have been investigated. DSC thermogram shows characteristics glass transition temperature at T_g = 775 K. Glasses doped with Au were subjected to heat treatment at 823 K with different annealing time and then, slowly cooled to room temperature show striking ruby color. SAED and TEM analyses have confirmed that f.c.c. Au nanoparticles of ~ 40 nm size are present in these glasses. An absorption peak centered on 563 nm has been observed in heat treated samples, which is attributed to surface plasmon resonance of gold nanoparticles. Nonlinear optical studies with open aperture Z-Scan technique show saturable absorption for heat treated samples at low intensity and reverse saturable absorption in samples without heat treatment at high intensity.     

Structural relaxation and optical properties in transparent nanocrystalline β-quartz glass-ceramic

We studied structural relaxation in a nanocrystalline β-quartz solid solution (s.s.) glass-ceramic through density measurement, and the effect of structural relaxation on its optical properties. The density of the glass-ceramic changed as structural relaxation proceeded in the glass phase. It was found that the glass-ceramic whose glass phase has a high fictive temperature shows a high optical transmittance because of less optical scattering. We also demonstrated that the refractive index difference between the crystal and glass phases can be calculated from the scattering coefficients of the specimens with different fictive temperatures. The calculated refractive index of the crystalline phase was in fair agreement with the indices of a high-quartz crystal.     

Influence of thermal history on the structure and properties of silicate glasses

We studied a set of float glass samples prepared with different fictive temperatures by previous annealing around the glass transition temperature. We compared the results to previous measurements on a series of amorphous silica samples, also prepared with different fictive temperatures. We showed that the modifications on the structure at a local scale are very small, the changes of physical properties are moderate but the changes on density fluctuations at a nanometer scale are rather large: 12% and 20% in float glass and silica, for relative changes of fictive temperature equal to 13% and 25% respectively. Local order and mechanical properties of silica vary in the opposite way compared to float glass (anomalous behavior) but the density fluctuations in both glasses increase with temperature and fictive temperature.     

Atomic dynamics in different regions of the potential energy surface

The atomic dynamics in two (bulk) metallic glasses, Ni₄₀Pd₄₀P₂₀ and Zr₅₅Cu₃₀Al₁₀Ni₅, were investigated by neutron inelastic scattering in different regions of the potential energy landscape, which are reached by slow cooling the bulk glasses and by hyper-quenching the same alloys. The results prove that the atomic dynamics depends also on the fictive temperature, i.e. the region of the potential energy surface, in which the glass is frozen in. Obviously the shapes of the basins or inherent structures are not the same everywhere on the potential energy surface, and the glass with a higher fictive temperature has more low energy modes than has the same glass with a lower fictive temperature. As results from computer simulation have suggested already, on moving to regions of lower mean potential energy (aging), part of theses low energy modes are transferred to the energy region of the calculated Debye cut-off energy. The difference between the vibrational entropies, calculated from the generalized vibrational density-of-states, which have been determined for both fictive temperatures, shows that the contribution from the vibrational entropy to the total entropy change, when moving through the potential energy landscape, is small for the two metallic glasses investigated. Structural relaxation of the hyper-quenched glass removes part of the additional low energy modes, but quantitatively possibly only at the low and perhaps also at the high-energy limit of the density-of-states. The wavelength dependence of the dynamics suggests that the additional low energy modes in the glass with the higher fictive temperature are not dominated by extended but more likely by localized modes.     

Microstructure and Texture Formation in Vacuum-deposited Silver Films

The role of the recystallization in the processes of microstructure and texture formation of silver films is compared for films: 1) deposited at high substrate temperatures (up to 720 K) and slowly cooled or quenched to room temperature; 2) deposited at room temperature and annealed at high temperatures. The grain growth distribution curves and the texture perfection are analysed. It is shown that the recrystallization processes taking place both during the slow cooling and during the annealing of the films lead to a formation of identical film structure with lower degree of texture perfection than in the case of quenched films.     

Adequacy test of the fictive temperatures of silica glasses determined by IR spectroscopy

Adequacy of the fictive temperature determined by the IR spectroscopy method was examined for various silica glasses by measuring the extent of the memory effect. The IR method of fictive temperature measurement of silica glasses relies upon the assumption that a silica glass has a silica structural band with a unique wavenumber when it has a particular fictive temperature. Silica glasses with various impurities or added components such as Cl, F, and OH were given a cross-over heat-treatment and the extent of the resulting deviation of the wavenumber during the second stage heat-treatment at a constant temperature corresponding to the apparent fictive temperature of the sample was determined. Silica glasses containing high concentrations of water or fluorine exhibited distinct memory effects while glasses with low water concentration or Cl did not. These results seem to indicate that the main source of the memory effect in silica glasses is the composition fluctuation rather than density fluctuation. Thus, the IR method of determining the fictive temperature is adequate for high purity silica glasses even when the glass samples have unknown thermal history.     

Unified approach for determining the enthalpic fictive temperature of glasses with arbitrary thermal history

We propose a unified routine to determine the enthalpic fictive temperature of a glass with arbitrary thermal history under isobaric conditions. The technique is validated both experimentally and numerically using a novel approach for modeling of glass relaxation behavior. The technique is applicable to glasses of any thermal history, as proved through a series of numerical simulations where the enthalpic fictive temperature is precisely known within the model. Also, we demonstrate that the enthalpic fictive temperature of a glass can be determined at any calorimetric scan rate in excellent agreement with modeled values.     

On the dependence of the properties of glasses on cooling and heating rates II: Prigogine-Defay ratio, fictive temperature and fictive pressure

In a previous analysis (J. Chem. Phys. 125 (2006) 094505) it was shown by us that - in contrast to earlier believe - a satisfactory theoretical interpretation of the experimentally measured values of the so-called Prigogine-Defay ratio, Π, can be given employing only one structural order parameter. According to this analysis, the value of this ratio has to be, in accordance with experimental findings, larger than one (Π > 1). This analysis is extended here and, in particular, the dependence of the value of Π on cooling and heating rates is studied. Finally, employing the general model-independent definition of internal (fictive) pressure and fictive temperature, developed by us (J. Non-Crystalline Solids 355 (2009) 653), it is shown how these parameters behave in dependence on temperature for different sets of cooling and heating rates. Some further consequences and possible extensions are discussed briefly.     

Calorimetric investigation of the structural relaxation and crystallization of amorphous Ge16Te84 alloys

Differential scanning calorimetric measurements have been performed on amorphous Ge₁₆Te₈₄ alloys; the study of the dependence of the cooling rate on the reciprocal fictive temperature yields the activation energy of the relaxation process; this value fits well that deduced from shear viscosity measurements. The enthalpy difference between the supercooled liquid and the crystal has been investigated by drop calorimetry on samples annealed at different temperatures below T_g, during different times. These results, combined with the former obtained by DSC lead to the enthalpy values of the metastable liquid system from 390 to 510 K.     

Microstructure and optical properties of phase-change Ge–Sb–Te nanoparticles grown by pulsed-laser ablation

Phase-change Ge–Sb–Te (GST) nanoparticles have been in-situ synthesized by a pulsed-laser ablation method. During the ablation process, growth parameters including temperature of heat treatment, pressure, and laser fluence are extensively explored. Scanning and transmission electron microscopy are used to study microstructure and phase formation of the nanoparticles. Fourier transform analysis of electron micrographs exhibits an evidence of existence of the stoichiometric single GST-225 phase. We have measured micro-Raman scattering spectra of commercially available GST-124, -147, and -225 bulk and GST nanoparticles. Lack of the amorphous Te–Te stretching mode near 150 cm⁻¹ from the Raman spectra of the bulk samples indicates that the samples are well-crystallized. From the measurements of GST nanoparticles with different growth conditions, we could get information towards the optimal growth conditions for better crystalline quality of the GST nanoparticles. Our results suggest that micro-Raman scattering spectroscopy can be used to study phases and phase changes in the GST bulk crystals and nanoparticles through local structural information, which is being developed for low-power non-volatile memory applications.     

Deceleration of surface structural relaxation in chlorine-containing silica glass due to chlorine volatilization

Both surface and bulk fictive temperatures of chlorine-containing silica glass were measured using the IR method, after thermal, mechanical and chemical treatments. A metastable equilibrium state at 1200 °C was first established for the glass by heat-treatment and a uniform fictive temperature was observed except for the sample surface created by polishing after the heat-treatment. The densified layer of the polished surface shifted the IR peak wavenumber, making the fictive temperature appear higher than the bulk. During the second heat-treatment at 950 °C, the sample with the as-heat-treated surface and uniform fictive temperature of 1200 °C developed non-uniform fictive temperature distribution with the bulk fictive temperature becoming lower than the surface fictive temperature. Usually, surface structural relaxation is faster than bulk structural relaxation and the surface fictive temperature becomes lower than the bulk fictive temperature when heat-treated at a lower temperature than the initial fictive temperature. The observed anomalous feature was attributed to chlorine volatilization from the glass surface layer creating a high viscosity surface layer. This conclusion was supported by the diffusion data of chlorine in the glass available in the literature.     

Melting and Crystallization Processes of EBBA I. Thermal Analysis

Melting and crystallization processes of EBBA (N-p-Ethoxybenzylidene-p'-butylaniline) have been studied by the method of thermal analysis and measurement of light transmittance. When the sample is cooled down from the nematic phase at a rapid cooling rate, solid phase (solid S) is formed directly. Solid S contains two solid modifications (solid S₁ and solid S₂. By heating the solid S, some amount of Solid S₁ is transformed into the nematic phase through the process of (melting of solid S₁ → crystallization to solid S₂ → melting of solid S₂). After the melting of solid S₁, some liquid crystalline state appears transiently. Solid S₁ is stabilized by the heat treatment at low temperature. The quantity of solid S₁ in solid S increases with the heat treatment time and/or with cooling at a low temperature.     

Fictive temperature dependence of subcritical crack growth rate of normal glass and anomalous glass

Subcritical crack growth rates of soda–lime–silicate glass, which is a typical normal glass, and silica glass, which is a typical anomalous glass, with different fictive temperatures were measured by the double-cleavage-drilled-compression (DCDC) fracture mechanics technique under both dry and humid atmospheres in order to clarify the effect of the fictive temperature on mechanical strength and fatigue. In the humid atmosphere, the soda–lime–silicate glass with a higher fictive temperature showed a slower crack growth rate than the same glass with a lower fictive temperature while the silica glass with a higher fictive temperature showed a faster crack growth rate than the silica glass with a lower fictive temperature. These results imply that normal glass with a higher fictive temperature is expected to show a higher mechanical strength compared with the same glass with a lower fictive temperature and anomalous glass with a higher fictive temperature is expected to show a lower mechanical strength than the same glass with a lower fictive temperature when tested in ambient air if the flaw size is the same. In the dry atmosphere, the fictive temperature effects on the crack growth rate in both glasses were small and within the experimental error.     

Low-energy excitations in polyvinyl chloride: Raman scattering and thermal properties

The low-energy excitations of a very fragile glass-former (in the sense of Angell), poly(vinyl chloride), have been studied by low-frequency Raman scattering and by measurements of the low-temperature heat capacity and thermal conductivity. Two different samples were investigated : one with a crystallinity of about 15%, the other quenched and amorphous, as measured by small-angle neutron scattering. The boson peak in Raman scattering was observed in both samples even at room temperature. A clear correspondance between the Raman boson peak, the excess of heat capacity and the plateau of thermal conductivity was shown. It is confirmed that the boson peak or the heat capacity excess are relatively small in this very fragile glass-former. However it is deduced that the high concentration of tunnelling systems in the amorphous sample is the result of a rapid quenching rather than an intrinsic property of fragile glass-formers.     

Thermal expansion of synthetic fused silica as a function of OH content and fictive temperature

A matrix of synthetic fused silica samples with OH contents from 30 to 1300 ppm and of a fictive temperature from 1000 to 1300 °C has been characterized regarding their thermal expansion with high precision. The thermal expansion increases with fictive temperature and drops with OH content. Although fictive temperature and OH are coupled due to the influence of OH on the relaxation of the network, an independent influence of the OH content on thermal expansion has been observed. This may provide a deeper insight into the impact of impurities incorporated into the fused silica network.     

Thermal strains in focusing channels of the stations for X-ray diffraction analysis in the Sibir-2 storage ring

The thermal load caused by the absorption of synchrotron radiation in X-ray optical elements of the Belok and RSA stations leads to optics elements heating and induces strains upon simultaneous cooling. The heating of the cooled first crystal in the double-crystal monochromator causes its bending and increases the reflected beam divergence, which, in turn, results in the monochromatic beam intensity loss [1]. Numerical simulation makes it possible to more accurately determine the strains, choose the optimal monochromator design, estimate the vertical sizes of the focal spot and wavelength resolution in the focusing channel, correctly design the system for cooling the mirror at the channel input, and choose a design providing the minimum temperature of the beam-limiting slit knives.     

Fictive temperature measurement of alumino-silicate glasses using IR spectroscopy

A simple IR reflection method was used in a previous study to determine the fictive temperature of silica glasses and a soda-lime glass. The IR method is based upon the fact that the silica structural band of a glass takes a unique wavenumber at a particular fictive temperature. When this method was applied to an alumino-silicate glass in this study, however, the IR reflection peak wavenumber of the glass surface was found to be strongly affected by the reaction of the glass with water vapor in the atmosphere. Still, it was possible to measure the fictive temperature of the alumino-silicate glass using IR spectroscopy by taking an IR reflection of the bulk sample after eliminating the surface layer affected by the reaction with water vapor. The IR peak wavenumber of the silica structural band decreased with increasing fictive temperature for the alumino-silicate glass, similar to silica glass.     

Exponential structural relaxation of a high purity silica glass

While most other glasses exhibit non-exponential structural relaxation characteristics even when the change of fictive temperature is small, a high purity silica glass exhibited exponential structural relaxation. This was demonstrated by showing that the non-exponential exponent or β value of the KWW function of the high purity silica glass approaches unity when the change of the fictive temperature approaches zero both from higher and lower temperature sides of the heat-treatment temperature. The non-exponentiality of the structural relaxation of this glass when fictive temperature change is finite is due to the change of relaxation time during the structural relaxation.     

Experimental confirmation of neoclassical Compton scattering theory

Incoherent X-ray scattering spectra of diamond and silicon crystals recorded on the BESSY-2 electron storage ring have been analyzed. All spectral features are described well in terms of the neoclassical scattering theory without consideration for the hypotheses accepted in quantum electrodynamics. It is noted that the accepted tabular data on the intensity ratio between the Compton and Rayleigh spectral components may significantly differ from the experimental values. It is concluded that the development of the general theory (considering coherent scattering, incoherent scattering, and Bragg diffraction) must be continued.     

Initial observations of dynamically heated bone

Understanding the chemical changes within bone during heat treatment has become essential within many fields including biomaterials, archaeology and forensic science. All current approaches report the systematic heating and cooling of bone specimens (a ‘static’ approach). These provide information on modifications to mineral structure and chemistry including recrystallisation and thermal decomposition from bone specimens cooled to room temperature. In order to understand these fundamental processes further, we adopted, for the first time, a dynamic heating protocol coupled to an X‐ray diffraction probe, which provides in situ analysis at temperature. This approach allows physico‐chemical processes to be observed at elevated temperatures for five different bone types: bovine, porcine, human, rostrum and red deer antler. The results, when compared to static heating studies, illustrate individually the effects of heating and cooling upon bone mineral. On heating, the onset of recrystallisation occurs rapidly over a short temperature range for all bone types. It is proposed the continued growth of the hydroxyapatite crystals is limited by the mineral to organic ratio. Investigation of the lattice parameters has also indicated significant differences between the bone types, suggesting species differentiation is possible using X‐ray diffraction analysis. Statistical analysis of the ‘a’ axis lattice parameter data revealed human bone is distinguishable from the other bone types.