Light scattering simulations relevant to crystallization of lithiumdisilicate glass

The virtual microstructures relevant to lithiumdisilicate glass crystallization have been created as an environment to compute the light scattering. The input data in computations include the number density of crystals, refractive indices of involved glassy and crystalline phases, the wavelength of the incident beam radiation, and the virtual sample slab thickness. The computations are performed under a number of simplifying conditions. They treat cases with proposed constant number densities of crystals, assuming their random volume distribution. The shape of the crystals is approximated by spheres. The results are expressed graphically in the form of theoretical optical transmission (OT) patterns, as they evolve on the crystal size axis. They reveal an influence of input data on computed OT. As evident from computations, some sets of input data will favor the real OT method's detection limits. The opposed sets of data will aid following the crystallization to the higher sample crystallinity degree α.     

Acoustic properties of aspirin in its various phases and transformation stages studied by Brillouin scattering

The acoustic behaviors of aspirin were studied in its crystal, liquid, glass states as well as transformation stages between them. The Brillouin doublet of the longitudinal acoustic (LA) mode propagating to the [100] direction of aspirin crystals showed a splitting in a temperature range of 393-413 K below the melting temperature, which indicated a softening and distortion of the layered aspirin crystal in its premelting stage. One LA mode was observed in the liquid and glassy phases of aspirin, consistent with Brillouin selection rule for isotropic materials. The acoustic damping in the glassy aspirin was systematically higher than that in the crystal aspirin, which was in contrast to ibuprofen materials. These suggested different activity of remnant local dynamics that could couple to the acoustic waves, persistent in the glassy state of these two representative pharmaceuticals. In the supercooled liquid phase, the Brillouin spectrum displayed a new spectral feature characterized by a high-frequency cutoff and a distributed low-frequency contribution other than the Brillouin peak of the amorphous aspirin. This could be ascribed to the formation of crystalline grains in the glassy matrix due to cold crystallization.     

Nanoindentation and Brillouin light scattering studies of elastic moduli of sodium silicate glasses

Compared to bulk techniques like Brillouin light scattering and ultrasonic measurements, nanoindentation provides a convenient way to investigate the Young's modulus of sodium silicate glasses with reasonably accurate results when Na₂O concentration is below 20 mol%. The large discrepancy in the Young's modulus for glasses with higher Na₂O contents measured by nanoindentation and the other two bulk techniques is resulted from the pile-up areas created around indents, which was evidenced by 3D AFM images. A structural understanding of the formation of these pile-up areas was gained from Raman spectra of sodium silicate glasses. A simple formula was proposed to correct the Young's modulus of sodium silicate glasses measured by nanoindentation.     

Lattice vibration and photoinduced light scattering in Co-, Cr- and Fe-doped lithium niobate

Raman scattering and photoinduced light scattering in Co-, Cr- and Fe-doped lithium niobate were examined. The A₁(TO) modes appear in E symmetry spectrum of the doped lithium niobate. Their intensities vary with different dopings. In the spectrum of z(yy)x geometry, the properties of the lowest-frequency E(TO) mode of the Cr-doped lithium niobate are different from those of pure, Co- and Fe-doped lithium niobate. The intensity of the A₁(TO) mode at 637cm^-1 I is decreased in doped lithium niobate compared with the pure crystal. We attribute these properties to both the photorefractive effect which is enhanced by dopants and to the different occupation of the doping ions. A light climbing effect was observed in Co- and Cr-doped lithium niobate for the first time. A higher photodamage threshold and quicker light climbing speed were found in Co- and Cr-doped lithium niobate in comparison with the light climbing effect in the Fe-doped lithium niobate. The results from the photoinduced light scattering experiments were compared with those from a Raman spectroscopic study.     

Broadband terahertz time-domain spectroscopy and low-frequency Raman scattering of glassy polymers: Boson peak of PMMA

The low-energy vibrational properties of polymethyl methacrylate (PMMA) were studied by terahertz time-domain spectroscopy and Raman scattering. The real and imaginary parts of a complex dielectric constant were accurately determined in the frequency range from 0.2 to 5.0 THz. The imaginary part of the dielectric constant shows a line-shape similar to the imaginary part of the Raman susceptibility measured by Raman scattering. These two spectra show broad peaks at about 2.3 THz. We also separately determined the Raman and far-infrared light-vibration coupling constants of the PMMA using the vibrational density of states determined by cold neutron inelastic scattering in the literature.     

An X-ray scattering study of hydrogenated nanocrystalline silicon with varying crystalline fraction

Using X-ray diffraction (XRD) and small angle X-ray scattering (SAXS), we probed the nanostructural features of several PECVD grown nc-Si:H thin films with varying crystalline volume fraction. XRD results of a mixed phase film, 70% a-Si:H and 30% c-Si:H, show these crystallites have a preferred [220] orientation in the growth direction. Another film with approximately 90% c-Si also shows elongated grains, but with a preferred [111] orientation. The SAXS results also show an increase in scattering intensity when compared to the mixed phase material. In the mixed phase material, models show that the electron density fluctuations between the amorphous and crystalline phases are not enough to explain the measured SAXS scattering. Hydrogen clustered at the crystallite boundaries and in void regions of the a-Si phase must be included as well.     

Crystallization and sintering behavior of phlogopite-soda lime composite

Sintering of (Soda-lime) glass, by means of 20-40 wt.% phlogopite, has been studied. According to TG and FT-IR, water loss of composite s by 8 wt.%, up to 1000 °C, caused the bloating and reduced the relative density. Dissolution of phlogopite with Diopside crystallization was detected up to 900 °C. Hardness of composites was increased by phlogopite content from 320 to 694 H_V and flexural strength was obtained in the range of 30-80 MPa.     

Spectroscopic studies of lead arsenate glasses doped with nickel oxide

Lead arsenate glasses containing different concentrations of NiO ranging from 0 to 1 mol% (in steps of 0.2 mol%) were prepared. The samples were characterized by X-ray diffraction and differential thermal analysis. A number of studies viz., optical absorption, thermoluminescence, magnetic susceptibilities and IR spectra, have been carried out on these glasses. The bands observed in the optical absorption spectra of the glasses have been analyzed using Tanabe-Sugano diagrams for d⁸ ion; the analysis indicates the presence of Ni²⁺ ions in both tetrahedral and octahedral positions. The increase in the concentration of NiO in the glass matrix shows a gradual transformation of nickel ions from tetrahedral positions to octahedral positions in the glass network. The thermoluminescence light output of the X-ray irradiated glasses has exhibited a glow peak at 353 K (with increasing intensity with an increase in the concentration of NiO) in addition to the conventional peak due to the recombination of electron-hole centers; this glow peak is identified due to ³T₂ → ³A₂ emission transition of octahedral Ni²⁺ ions. The value of the magnetic moment evaluated from the measured magnetic susceptibility show a decreasing trend from 3.84 to 3.10 μ_B with the increase in the concentration of NiO. All these studies indicate an increasing presence of octahedral (lasing) Ni²⁺ ions in these glasses with the increase in the concentration of NiO.     

X-ray scattering studies of polymeric zirconium species in aqueous xerogels

X-ray scattering in the small angle range was used to investigate the structure and size of the polymeric species present in zirconium acetate (ZrAc)-based gel powders (GP) and thin films (TF). The formation of amorphous zirconia aggregates/linear polymers was studied by measuring their gyration radii and their correlation and hydrodynamic lengths via Guinier, `longrods', Zimm and Porod plots. Scattering data obtained in this investigation suggest that both amorphous ZrAc-based GP and TF contain `tetrameric' units, arranged in a cylindrical fashion, that polymerize upon thermal treatment. Housdorff fractal dimensionality, D, of amorphous zirconia GP (D∼2.25) and TF (D∼2.5) indicates a diffusion-limited aggregation mechanism. Tricyclic cluster aggregates (Porod D∼1.85) with a M_w∼12 000 were found within amorphous ZrAc-based GP. This structure is preserved over the entire curing range. In contrast, a linear polymeric chain (Porod D∼1.52), with a M_w∼20 000 below 165 °C and ∼13 000 at higher temperatures, was suggested for amorphous ZrAc-based TF.     

The Temperature Study of the Elastooptic Properties of SrLaAlO4 and SrLaGaO4 Crystals by Brillouin Light Scattering

The temperature study of the elastooptic properties of SrLaAlO₄ (SLA) and SrLaGaO₄ (SLG) crystals has been reported. The results obtained are discussed in terms of the nature of the oxygen point defects, which might be created in the crystals during the growth process.     

Raman scattering study of crystalline and melting states of BaO·2B2O3

Melting and crystallization scenarios of barium tetraborate BaB₄O₇ (BaO·2B₂O₃) are studied in situ by Raman spectroscopy. It is shown that the scenario depends on the temperature–time history of melt. Crystallization conditions of the beta modification of barium tetraborate (β-BaB₄O₇) from a stoichiometric glass structure BaO·2B₂O₃ were investigated.     

Optical properties of KGd(WO4)2 single crystals studied by Brillouin spectroscopy

The results of a study of KGd(WO₄)₂ single crystals by Brillouin scattering method are presented. The Brillouin spectra for the acoustic phonons propagating in the [100], [010], [001], [110] and [101] directions, taken in 90° and 180° scattering geometry at room temperature have been recorded. Using the Brillouin spectroscopy the refractive indices for some directions of KGd(WO₄)₂ crystals were determined. The refractive indices were also calculated for the same directions by the rotation transformation of the principal optical axes of the optical indicatrix to the crystallographic directions of KGd(WO₄)₂ crystals. Moreover, some anomalies of the acoustic phonons propagating connected with birefringence of KGd(WO₄)₂ crystals were discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A total X-ray scattering study of MnFe2O4 nanoparticles dispersed in a silica aerogel matrix

Structural information on a MnFe₂O₄-SiO₂ nanocomposite aerogel and on the pure silica aerogel matrix were obtained by total X-ray scattering experiments. The total pair distribution function of the silica aerogel is in agreement with literature data on melt-quenched silica. The total pair distribution function of the nanocomposite contains the contribution of all the pair correlations of the atomic species making the interpretation more difficult. The difference curve obtained by subtracting the total pair distribution function of the matrix from that of the nanocomposite, allows to selectively study the structural environment of the nanoparticles.     

Analysis of waveguide silica glasses using Raman microscopy

A spectroscopic method to determine dopant concentrations in silicas used in silica on silicon planar waveguides has been developed. Raman spectroscopic measurements in the range 740 cm⁻¹–1370 cm⁻¹ of cross-sections of the glass layers identified correlations between simple, rapidly calculated, spectral features related separately to each of the three dopants, boron, phosphorous and germanium, and the wt% analyses results for these dopants from inductively coupled plasma mass spectrometry (ICP-MS) measurements on fragments from the respective wafers. The calibration wafers comprised a set of monitor wafers with dopant concentrations spanning the ranges used in devices. The Raman-based analyses were able to determine boron and phosphorous wt% s in boro-phosphosilicate cladding glasses with accuracies of ≈0.1 wt% and germanium wt% s in core glasses with an accuracy of at least ≈0.3 wt% (small batch size). The method, which performed successfully in blind tests, provides a spatially resolving and rapid alternative to ICP-MS analyses of monitor wafers. Exploratory face-on measurements were performed on device wafers. Spectra of the cladding, core and underlayer were obtained from AWG samples. The effects of the confocal volume’s finite size and refractive index differences were observed. Exploratory measurements using UV Raman excitation showed potential advantages for cladding glass analyses.     

Correlation of ion dynamics and structure in superionic glasses and nanocomposites

Ion dynamics of AgI-doped Ag₂O–TeO₂ glasses and Ag₂S doped glass nanocomposites have been studied using impedance spectroscopy and correlated with their structures investigated using Fourier transform infrared spectroscopy. The composition dependences of the dc conductivity and the activation energy of these glasses and nanocomposites have been compared with those of AgI-doped silver phosphate and borate glasses. We have studied the ion dynamics in the framework of the power-law and the electric modulus formalisms. We have established a correlation between the crossover rate of the mobile silver ions and the rearrangement of the structural units of glassy networks. The scaling of the conductivity spectra has been used to interpret the temperature and composition dependence of the relaxation dynamics. Analysis of the dielectric relaxation in the framework of modulus formalism indicates an increase in ion–ion cooperation in the glass compositions with increasing AgI content.     

Low-temperature properties of glassy and crystalline states of n-butanol

We present low-temperature measurements of the specific heat and the thermal conductivity for the three solid phases of n-butanol, namely glass, crystal and “glacial” phases. Whereas crystal and glass ones are found to exhibit the expected thermal behavior for crystalline and non-crystalline solids, respectively (i.e. Debye theory for crystals, and universal low-temperature properties with a boson peak and a concomitant plateau in the thermal conductivity for glasses), the so-called “glacial phase” behaves as a very defective crystal, confirming earlier work that identifies it as a mixed phase of nanocrystallites and a disordered matrix. We have also measured longitudinal and transverse sound velocities at low temperatures for the glass phase. The elastic Debye coefficient and Debye temperature of the glass determined from these measurements are found to agree very well with the calorimetric ones obtained from a SPM analysis of the specific heat.     

Quasi-elastic neutron scattering of cyanobiphenyl compounds with different terminal chains

Quasi-elastic neutron scattering measurements were performed for five cyanobiphenyl compounds with different terminal chains (5CB, 5*CB, 8OCB, 8*OCB and 6O2OCB) in their liquid and liquid-crystalline phases to investigate the molecular dynamics. The spectra were successfully decomposed into two components, indicating that two types of molecular motions are involved. For the broad (or fast) component, the temperature dependence as well as the momentum transfer dependence did not differ very much among those compounds. For the narrow (or slow) component, on the other hand, the compounds with a branched alkyl-chain (5*CB and 8*OCB) gave significantly smaller diffusion constants than the others. A molecular dynamics simulation for 5*CB and 5CB suggests that the reorientational motion of the whole molecule around the long molecular axis is responsible for the broad component, whereas a diffusive motion of the terminal chain is responsible for the narrow one.     

Casting vacuum effects on the precipitates and magnetic properties of Fe-based glassy alloys

The crystalline precipitates and magnetic properties of the Fe₆₁Co_9 − xZr₈Mo₅W_xB₁₇ (x = 0 and 2) cylinders prepared under various vacuum conditions were investigated in this paper. The fraction of the crystalline precipitates and liquidus temperature of the samples with tungsten content c_W = 0 decease with decreasing vacuum, while they increase in the samples with c_W = 2 at.%. For both tungsten contents, with decreasing vacuum, the magnetization at room temperature M_start and Curie temperature T^h_c of the samples decrease gradually, but the increment of magnetization ΔM_800 K at 800 K after heating to 973 K increases and the Curie temperature T^c_c of the residual amorphous matrix shows a decreasing tendency simultaneously. Meanwhile, with decreasing vacuum, Zr-B compounds tend to precipitate easily out from the melt or to remain undissolved during casting, and eutectic Fe-B compounds tend to be formed easily after heating to 973 K. The existence of Zr-B and Fe-B compounds changes the boron content in the residual melt/matrix and consequently affects the magnetic properties of the samples in the as-quenched state and after heating to 973 K.     

Raman scattering study on Ga1–x Mnx As prepared by Mn ions implantation,deposition and post‐annealing

Raman scattering measurements have been performed in Ga_1–x Mn_x As crystals prepared by Mn ions implantation, deposition, and post‐annealing. The Raman spectrum measured from the implanted surface of the sample shows some weak phonon modes in addition to GaAs‐like phonon modes, where the GaAs‐like LO and TO phonons are found to be shifted by approximately 4 and 2 cm^‐1, respectively, in the lower frequency direction compared to those observed from the unimplanted surface of the sample. The weak vibrational modes observed are assigned to hausmannite Mn₃O₄ like. The coupled LO‐phonon plasmon mode (CLOPM), and defects and As related vibrational modes caused by Mn ions implantation, deposition, and post‐annealing are also observed. The compositional dependence of GaAs‐like LO phonon frequency is developed for strained and unstrained conditions and then using the observed LO_GaAs peak, the Mn composition is evaluated to be 0.034. Furthermore, by analyzing the intensity of CLOPM and unscreened LO_GaAs phonon mode, the hole density is evaluated to be 1.84×10¹⁸ cm^‐3. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)