Physical aging effects in selenide glasses accelerated by highly energetic γ-irradiation

Effect of ⁶⁰Co γ-irradiation on As–Se glasses stored for 20 years and subjected to saturated natural physical aging is studied using differential scanning calorimetry. It is shown that γ-irradiation activates further physical aging, which leads to an increase in glass transition temperature and endothermic peak area near glass transition region for As_xSe_100−x samples with x < 30. The observed changes are associated with additional structural relaxation of radiation-modified glass network.     

Glassy state and structure of Sn–Sb–Se chalcogenide alloy

The effect of Sn addition on the glass transition and structure of c-Sb₂₀Se₈₀ chalcogenide alloy have been studied by X-ray diffraction and differential scanning calorimetric studies. The increase in the glass forming region and the glass transition temperature with the addition of Sn is discussed by considering the formation of [SnSe₄] tetrahedra, another type of network former, which inhibits the crystallization. The differential scanning calorimetric studies on Sn_xSb₂₀Se_80−x (8 ⩽ x ⩽ 18) glassy samples reveal a single glass transition temperature for all values of x while a single crystallization peak was obtained only for 10 ⩽ x < 12. The X-ray diffraction studies reveal that the glass crystallizes to Sb₂Se₃ and SnSe₂ phases upon annealing. The glass formation and composition dependence of glass transition temperature in the Sn–Sb–Se chalcogenide alloy could be understood by considering the topological phase transitions and a chemically ordered network model.     

Effects of graphite additive on dielectric properties and microwave absorption properties of zinc-containing foam glass

This paper reports effects of graphite additive on dielectric properties and microwave absorption performances of zinc-containing foam glasses. Changes of pore structure of porous glass are analyzed. One-dimensional zinc oxide crystal whiskers on walls of foam glass are observed. With the graphite additive increases, both real (ε′) and imaginary (ε″) parts of complex permittivity increase from ~ 3.25 and ~ 0.2 to ~ 7.5 and ~ 2.8, respectively. Microwave reflection loss of porous glass was calculated based on the permittivity in the range of 8.2–12.4 GHz(X-band). Reflection loss of foam glass decreases as graphite additive and the sample with 2.0 wt% graphite additive achieve reflection loss less than ? 10 dB in whole X-band with thickness ranging from 2.3 to 3.5 mm. Linear relation between reduction of reflectivity and increase of graphite content is achieved. The results show that changing foaming agent additive is an efficient way to design dielectric and microwave absorption properties of foam glass. Foam glass with 1.0 wt% graphite additive may find application in photocatalytic degradation of many environmental pollutants due to its considerable zinc oxide whiskers.     

Octahedral fluoride glasses: Raman spectra and structure of niobium pentafluoride

Raman spectroscopy is used to characterize the NbF₅ phases in the temperature range 80–500 K. A new clear glass is formed by quenching the melt to liquid nitrogen temperatures having a glass transition at ～206 K and crystallization at ～233 K. For all phases including the melt, the glass, the supercooled liquid, the crystalline solid and the gas, the Raman spectra show a rather common high frequency band at ～760 cm^?1 which is attributed to the Nb–F terminal frequency of partially bridged ‘NbF₆’ octahedra. Based on the systematics of the Raman spectra for all phases and the literature physicochemical data a model is proposed for the glass and the liquid phases where ‘NbF₆’ octahedral bridged in cis and/or trans configurations form a variety of cyclic and/or chain structures which intermix building up the overall structure. At exceptionally low energies (<11 cm^?1) a rather weak in intensity Boson peak is observed in the glass which shifts to even lower energies with increasing temperature. Librational and/or tortional motions of the bridged octahedra participating in the glass structure are possible candidates for the origin of this peak.     

Structural and dynamical properties of Fe78Si9B13 alloy during rapid quenching by first principles molecular dynamic simulation

Structural evolution of the Fe₇₈Si₉B₁₃ alloy during rapid quenching was investigated by ab initio molecular dynamics simulation. The second peak splitting has been perceived even at 1473 K in the partial pair correlation functions though not in the total pair correlation function. The (0, 3, 6, 0) polyhedra are abundant in the liquid state while the distorted (0, 3, 6, 0) polyhedra are the featured local structure around B atoms in the amorphous state. The diffusion coefficients of the three elements are evaluated to understand the dynamics of quenching. From 1173 to 873 K the three coefficients are coherent. We think this temperature range corresponds to the supercooled liquid region, and 873 K serves as the glass transition temperature.     

The boson peak in melt-formed and damage-formed glasses: A defect signature?

We describe the preparation and characterization of a glassy form of the moderately good glassformer PbGeO₃, by mechanical damage, and compare its properties with those of the normal melt-quenched glass and the crystal. The damage-formed glass exhibits a DSC thermogram strikingly similar to that of a hyperquenched glass, implying that it forms high on the energy landscape. The final glass transition endotherm occurs within 4 K (0.006T_g) of that of the melt-quenched glass, but crystallization occurs at a lower temperature, as if pre-nucleated. In particular, we have studied the low frequency vibrational dynamics of the alternatively prepared amorphous states in the boson peak region, and find the damage-formed glass boson peak to be almost identical in shape to, but more intense than, that of the normal melt-formed glass, as previously found for hyperquenched glasses. In view of the quite different preparation procedures, this similarity would seem to eliminate equilibrium liquid clusters as a source of the boson peak vibrations, but leaves plausible a connection to force constant fluctuations or to specific vitreous state defects.     

Glass formation of Ti–Ni–Sn ternary alloys correlated with TiNi–Ti3Sn pseudo binary eutectics

Glass-forming ability (GFA) of Ti–Ni–Sn ternary alloys was investigated. Applying recent models based on atomic size ratio and efficient packing, the composition favoring the glass formation is predicted. Our experiments indicate that the optimized glass-forming composition is located at Ti₅₆Ni₃₈Sn₆, with the critical thickness of complete glass formation approaching 100 μm for the melt-spun ribbons. The Ti₅₆Ni₃₈Sn₆ metallic glass exhibits a sizable supercooled liquid region (ΔT_x) of about 35 K and a reduced glass transition temperature (T_rg) of 0.52. We demonstrate that the glass formation of the Ti₅₆Ni₃₈Sn₆ alloy correlates with the (L → TiNi + Ti₃Sn) pseudo binary eutectic reaction in Ti–Ni–Sn ternary system, which has an invariant temperature and composition at ～1370 K and ～Ti₅₈Ni₃₄Sn₈, respectively. With respect to Sn-free Ti–Ni binary alloys, the GFA is enhanced for the Ti–Ni–Sn ternary alloys, but the improvement is limited possibly due to changes in the crystalline phases competing with glass formation.     

The transformation balance between two types of structural defects in silica glass in ion-irradiation processes

Structural modification in silica glass irradiated by Au ions was investigated by ultraviolet (UV), photoluminescence and Raman spectrum at the energies from 0.5 to 8 MeV with a fluence of 5 × 10¹³ cm^? 2. In this transit energy region, both nuclear energy loss and electronic energy loss are not negligible. It was found that both the formation of irradiation-induced intrinsic defects and structural transformation from irregular large ring structure (LRS) to small three- and four-member ring structures (SRS) are dominated by the nuclear energy loss. Furthermore, unlike the case of irradiation with β, γ or proton, the concentration of non-bridging oxygen hole center is much enhanced followed with a distinct peak appearing at 5.05 eV in the UV absorption spectra that is attributed to divalent Si. The results suggest that the structural modification in silica glass in the transit energy region is dominated by nuclear energy loss. A mutual transformation balance model among irradiation-induced intrinsic defects, LRS and SRS is established to interpret the identical variation tendencies of intrinsic defects and structural transformation with ion energy.     

Nearly constant dielectric loss of polyhydric alcohols

Complex permittivity measurements have been performed on a series of polyhydric alcohols (glycerol, threitol, xylitol and sorbitol) and mixtures of glycerol–xylitol and xylitol–sorbitol in the frequency range between 100 Hz and 1 MHz at temperatures from 293 K down to 50 K. It was found that all the systems including the mixtures show the nearly constant dielectric loss (NCL) at temperatures far below the glass transition temperature. The parameters describing the NCL depend on the number of carbons in the molecules. This relation can also be applied for the mixture with the mean values for the number of carbons. The parameters describing the behavior of the α process, such as the fragility index, depend the number of carbons in this series of polyhydric alcohols. Degree of freedom in the intermolecular interactions connected with the fragility index can be considered to relate to the NCL. This is consistent with the caged dynamics as a possible microscopic origin for the NCL. Although the fast β process is not denied by the NCL, coexistence of these processes being able to explain the dielectric loss minima, should be examined experimentally in future.     

Slow and fast dynamics in glycerol–water mixtures

We discuss the relaxation dynamics of glycerol–water mixtures as studied by broadband dielectric spectroscopy (BDS) and differential scanning calorimetry (DSC). BDS studies were performed in a frequency range of 1 Hz to 250 MHz at temperatures ranging from 173 to 323 K and DSC measurements were made between 138 and 313 K. The experimental results obtained for the glycerol-rich mixtures in terms of dielectric loss ‘master plots’ suggest that the main dielectric relaxation process, as well as the high frequency ‘excess wing’ and dc-conductivity, follow the same temperature dependence. This result indicates that all of these processes are based on the same physical origin. A new phenomenological relationship for the complex dielectric permittivity is proposed. The structural and dynamic properties of glycerol–water mixtures are discussed. The experimental data for water-rich mixtures show the existence of a critical concentration of 40 mol% of glycerol that relates to the numbers of hydrogen bonds of glycerol and of water molecules. Below this concentration, water cooperative domains appear, coexisting with the glycerol cooperative domains. Below 20 mol% of glycerol, ice nanocrystals appeared that led to three relaxation processes; result from ice, mesoscopic glycerol–water domains, and water on the interface between former two.     

Roughness of glass surfaces formed by sub-critical crack growth

This paper presents a study on the roughness of glass fracture surfaces formed as a consequence of sub-critical crack growth. Double-cantilever-beam specimens were used in these studies to form fracture surfaces with areas under well-defined crack velocities and stress intensity factors. Roughness depends on crack velocity: the slower the velocity, the rougher the surface. Ranging from approximately 1 × 10⁻¹⁰ m/s to approximately 10 m/s, the velocities were typical of those responsible for the formation of fracture mirrors in glass. Roughness measurements were made using atomic force microscopy on two glass compositions: silica glass and soda lime silica glass. For silica glass, the RMS roughness, R_q, decreased from about 0.5 nm at a velocity of 1 × 10⁻¹⁰ m/s to about 0.35 nm at a velocity of 10 m/s. For soda lime silica glass, the roughness decreased from about 2 nm to about 0.7 nm in a highly non-linear fashion over the same velocity range. We attributed the roughness and the change in roughness to microscopic stresses associated with nanometer scale compositional and structural variations within the glass microstructure. A theory developed to explain these results is in agreement with the data collected in the current paper. The RMS roughness of glass also depends on the area used to measure the roughness. As noted in other studies, fracture surfaces in glass exhibit a self-affine behavior. Over the velocities studied, the roughness exponent, ζ, was approximately 0.3 for silica glass and varied from 0.18 to 0.28 for soda lime silica glass. The area used for these measurements ranged from (0.5 μm)² to (5.0 μm)². These values of the roughness exponent are consistent with values obtained when the scale of the measurement tool exceeds a critical size, as reported earlier in the literature.     

Acoustic damping in Li2O–2B2O3 glass observed by inelastic X-ray and optical Brillouin scattering

The dynamic structure factor of lithium-diborate glass has been measured at several values of the momentum transfer Q using high resolution inelastic X-ray scattering. Much attention has been devoted to the low-Q-range, below the observed Ioffe–Regel crossover q_IR ≃ 2.1 nm⁻¹. We find that below q_IR, the linewidth of longitudinal acoustic waves increases with a high power of either Q, or of the frequency Ω, up to the crossover frequency Ω_IR ≃ 9 meV that nearly coincides with the center of the boson peak. This new finding strongly supports the view that resonance and hybridization of acoustic waves with a distribution of rather local low frequency modes forming the boson peak is responsible for the end of acoustic branches in strong covalent glasses. Further, we present high resolution Brillouin light-scattering data obtained at much lower frequencies on the same sample. These clearly rule out a simple Ω²-dependence of the acoustic damping over the entire frequency range.     

Brillouin scattering of glass-forming KCN:x mixture solutions within 0.58 < x < 0.64

Few investigations of glass transition in the glass-forming materials [KNO₃]_x[Ca(NO₃)₂]_(1−x) (KCN:x), except at x = 0.6 have been performed. The glass-forming range in KCN:x were obtained to be 0.58 < x < 0.64 from in situ observation using a stereoscope. For x < 0.58 and x > 0.64, crystal growth was observed. Brillouin scattering measurements in these mixture solutions, mainly for x values of the glass-forming region, have been performed as a function of temperature. From the thermal compressibilities β estimated by fitting analysis, their gradients from the glass transition temperature to about 170 °C (=T_cr) depend on x. This means that the ways of approaching the glass state from T_cr are slightly different in KCN:x. This T_cr is suggested to be a special temperature in the middle of the supercooling region during cooling and to specify the boundary from a liquid-like state to a solid-like state.     

Preparation of TiO2–Na2O glass by sol–gel method and structural characterization

The applicability of sol–gel process in glass formation of binary system, (100 − x)TiO₂–xNa₂O (x = 10, 20, 30), was investigated and the glasses were prepared successfully by the sol–gel process for the first time. The process of glass formation was checked by using X-ray diffraction measurement and DTA–TG analysis. In the baking step, a DTA peak related to the crystallization of gel was found. The short-range structure of glassified samples was studied by neutron scattering measurement. It is found from the results of neutron scattering measurement that the coordination number of O atom around Ti atom is about 4, and the O atoms around Ti atom form a planer square rather than a regular tetrahedron.     

Thermal conductivity of glassy primary mono-hydroxylalcohols

Thermal conductivity κ(T) data for homologous series of primary mono-hydric alcohols – methanol, ethanol, 1-propanol, 1-butanol – within their molecular glass states are analyzed within the temperature region stretching from 2 K up to the glass transition T_g. Below 7 K κ(T) increases with the number of carbon atoms in the molecule. Furthermore, its temperature dependence exhibits a behavior akin to that predicted by the phenomenological model of soft potentials (SPM). The data are then rationalized in terms of the SPM parameters such as characteristic energy W and the parameter ¯С which measures the strength of the coupling of acoustic modes with two-level systems. The dependence of such parameters upon the molecular mass of the alcohol seems to agree with the SPM predictions. The parameters ¯С and W were used to calculate the boson peak energies. The values obtained agree well with literature data.     

Thermal and optical properties of TeO2–ZnO–BaO glasses

We report the results of a systematic study of the thermal and optical properties of a new family of tellurite glasses, TeO₂–ZnO–BaO (TZBa), as a function of the barium oxide mole fraction and compare them with those of TeO₂–ZnO–Na₂O (TZN). The characteristic temperatures of this new glass family (glass transition, T_g, crystallization, T_x, and melting, T_m) increase significantly with BaO content and the glasses are more thermally stable (greater ΔT = T_x ? T_g) than TZN glasses. Relative to these, Raman gain coefficient of the TZBa glasses also increases by approximately 40% as well as the Raman shift from ~ 680 cm^? 1 to ~ 770 cm^? 1. The latter shift is due to the modification of the glass with the creation of non-bridging oxygen ions in the glass network. Raman spectroscopy allows us to monitor the changes in the glass network resulting from the introduction of BaO.     

Temperature dependence of electric conductivity of bamboo coral skeleton and glass sponge spicules,the marine origin biomaterials

Natural structural biomaterials of marine origin including corals and sponges provide an abundant source of novel bone and cartilage replacements. Even though mechanical and optical properties of these natural biocomposites have been treated extensively in the literature, there is no available data on their electric properties. In the paper electric conductivity along with enthalpy of the process of electric charge conduction process were determined. The conductivity–temperature (σ–T) characteristics of native and deproteinated spicules of marine glass sponge and the mineral phase of bamboo corals provide information on the process of water release and phase transition in collagen. Denaturation temperature for coral was found at 203 °C. The peaks at 160° and 195 °C for the native glass sponge spicules may be explained by more complicated denaturation process where probably, less ordered regions of collagen denaturated at lower temperature and regions of high crystallinity at higher temperature. The decrease in electric conductivity observed after deproteination of glass sponge spicules showed that electric charge in the native glass sponge spicules was probably transported along the paths formed by collagen. Deproteination changed also σ–T characteristics, the kink at 140 °C is caused by glass transition of collagen, whereas the peak at 175 °C was probably caused by thermal denaturation of residual collagen of perturbed structure.     

Regenerator performance below 4 K in Tm-based bulk metallic glasses

The main obstacle for reaching low temperatures below 4 K using cryocoolers was the inefficiency of the regenerator materials. We report that large volumetric specific heat below 4 K in a wide temperature range has been obtained in Tm-based bulk metallic glasses, and the peak temperature of specific heat peak is tunable. We show that the amorphization of rare-earth based crystalline alloys and the lower magnetic transition temperature of spin glass behavior in the glasses result in the specific heat anomaly below 4 K. The large and tunable specific heat anomaly below 4 K indicates the potential regenerator performance of the glassy materials for sub-4 K cryocoolers.     

Dynamic properties of solvent confined in silica gels studied by broadband dielectric spectroscopy

We report the results of a broadband (10⁻²–10⁷ Hz) dielectric spectroscopy study on a solvent system (glycerol–water solution) confined in a porous silica matrix. The dielectric relaxation of the system is studied as a function of both temperature (120–280 K) and solvent composition (0–36 glycerol molar percentage), at constant matrix composition. Our data show that glycerol–water systems confined inside silica gel are characterized by a very complex dynamics quite different from that observed in solution, thus indicating that confinement may deeply modify solvent dynamics. Indeed in addition to the relaxation processes similar to those occurring in bulk samples, new dielectric relaxations are detected: two non-collective relaxations, attributed to water molecules strongly interacting with pore surfaces and to the glycerol trapped within the matrix structure, respectively; a relaxation in the glycerol free sample (and in samples at very low glycerol content) almost coincident with that observed in other different confinement conditions and governed by geometrical confinement per se. Moreover, at high glycerol content we observe two non-Arrhenius processes at least 4 order of magnitude slower than solution-like main relaxation; at low glycerol content the two above relaxations merge and show a fragile to strong transition at about 200 K.     

Fast relaxation processes in glasses as revealed by depolarized light scattering

Applying tandem-Fabry-Perot interferometry together with a double monochromator, depolarized light scattering spectra were measured in order to investigate the fast relaxation processes and vibrations in molecular, ionic and polymeric glasses in the 1–5000 GHz range covering temperatures from the glass transition temperature T_g down to some 10 K. In addition to the boson peak, the spectra reveal quasi-elastic contributions that we attribute to (i) a nearly constant loss in the frequency range below ≅10 GHz and (ii) a power-law contribution with positive exponent α at higher frequencies. In the majority of glasses the latter may be attributed to thermally activated dynamics in asymmetric double well potentials as previously found for the light scattering spectra in silica. Following the Gilroy–Phillips model the exponent α shows a master curve as a function of T/V₀ for the various glasses, where V₀ specifies the width of the exponential distribution of barriers g(V), i.e., g(V) ∝ exp(−V/V₀). The parameter V₀ is found to be ∼T_g/2 in most cases. The relative strength of the dynamics in asymmetric double well potentials and the nearly constant loss contribution is different in the glasses studied.