Temperature range of the liquid–glass transition

It has been shown that the currently used method for calculating the temperature range of δT_g in the glass transition equation qτ_g = δT_g as the difference δT_g = (T₁₂–T₁₃) results in overestimated values, which is explained by the assumption of a constant activation energy of glass transition in deriving the calculation equation (T₁₂ and T₁₃ are the temperatures corresponding to the logarithmic viscosity values of logη = 12 and logη = 13). The methods for the evaluation of δT_g using the Williams–Landel–Ferry equation and the model of delocalized atoms are considered, the results of which are in satisfactory agreement with the product qτ_g (q is the cooling rate of the melt and τ_g is the structural relaxation time at the glass transition temperature). The calculation of τ_g for inorganic glasses and amorphous organic polymers is proposed.     

Importance of solute–solute interactions on glass formability

Microalloying experiments on amorphous Al₈₄La₄Er₂Ni₈TM₂ alloys were performed with the substitution of all 3d TM (transition metal) elements and one 4d TM element. The critical thickness of the amorphous alloys was used as a criterion for glass formability in this system. The results show that, other than atomic size differences and the negative heats of mixing among the solvent and solute atoms, the atomic interactions among the solute atoms play an important role on glass formation. When the solute–solute interaction becomes repulsive (positive heat of mixing), glass formability suffers. Similarly, when the solute–solute interaction becomes highly attractive, exceeding that between the solvent and solute atoms, glass formability is also degraded. Evaluation of a large number of known multicomponent bulk metallic glasses provides additional support to these conjectures. This study shows that the solute–solute interaction plays an important role in glass formation, which has not been recognized previously.     

Optimized diode-pumped passive Q-switched ytterbium–erbium glass laser

A model taking into account the up-conversion processes involving the upper laser level and the presence of the unpumped regions within the active element along with the lasing transitions has been developed for the passive Q-switched ytterbium?Cerbium glass laser which was transversally pumped by the laser diode arrays. The results of the simulation allow determining the working point providing the stable and long-term operation of the laser. The correctness of the proposed optimized model was experimentally proved by means of a comparative investigation of the utmost permissible output lasing characteristics. The maximum output lasing pulse energy up to 16.5 mJ with the pulse duration of 11.5?C16.0 ns at the wavelength of 1.535 ??m has been achieved with the rectangular active element for the length of 32 mm.     

Nanomechanical properties inside the scratch grooves of soda–lime–silica glass

Zn_2?2x Mn_2x GeO₄ (x=0, 0.001, 0.01) phosphors were prepared by conventional solid state reaction technique. X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), diffuse reflection spectra, photoluminescence (PL), and cathodoluminescence (CL) spectroscopy were utilized to characterize the synthesized phosphors. The Mn²⁺-activated Zn₂GeO₄ phosphors exhibit narrow emission band at 532 nm under the excitation of ultraviolet light, which due to the ⁴T₁(⁴G)–⁶A₁(⁶S) transition of Mn²⁺ ions. Also it is observed that there exists energy transfer between the Zn₂GeO₄ host lattice and the activator (Mn²⁺). Under excitation of low-voltage electron beams, Zn₂GeO₄:Mn²⁺ shows strong green emission band dominating at 535 nm, corresponding to the ⁴T₁(⁴G)–⁶A₁(⁶S) emission of Mn²⁺ ions. The emission intensity and chromaticity coordinates of Zn₂GeO₄:Mn²⁺ as a function of accelerating voltage and the filament current were also investigated.     

Formation of sub-surface silver nanoparticles in silver-doped sodium–lead–germanate glass

The formation of silver nanoparticles in 60GeO₂–20PbO–20Na₂O bulk glass doped with 0.15 wt% of Ag has been studied by optical methods in the near ultraviolet-to-near infrared and mid-infrared ranges. A clear optical absorption band, which grows when increasing the annealing temperature, is observed around 460 nm, as a consequence of the surface plasmon resonance in the Ag nanoparticles. From the simultaneous analysis of optical transmittance and spectroscopic ellipsometry spectra in the near ultraviolet-to-near infrared range, it is demonstrated that the nanoparticles are surprisingly formed only in a thin layer (some tens of nm thick) underneath the sample surfaces. The potential of such a simultaneous optical analysis for determining the localization of the nanoparticles in glasses of any nature is underlined. Based on the results of a complementary mid-infrared spectroscopy characterization, the processes involved in silver migration to the surfaces and further aggregation to form nanoparticles are discussed.     

Effect of scratching speed on deformation of soda–lime–silica glass

The grinding and polishing of a fundamentally brittle material like glass to an utmost precision level for ultra-sophisticated applications ranging from mobile devices to aerospace as well as space shuttle components to biomedical appliances pose a big challenge today. Looking simplistically, the grinding and polishing processes are basically material removal by multiple scratching at a given speed. Unfortunately however, the role of the scratching speed in affecting the material removal mechanism in soda–lime–silica (SLS) glass is yet to be comprehensively understood. Therefore, the present work explores the surface and subsurface deformation mechanisms of SLS glass scratched under a normal load of 5 N at various speeds in the range of 100–1000 μm?s^?1 with a diamond indenter of ～200 μm tip radius. The results show important roles of the time of contact, the tensile stress behind the indenter and the shear stress just beneath the indenter in governing the material removal mechanisms of the SLS glass.     

Crystallization kinetics of the TeO2–BaO glass system

Tellurite glasses of the system (100–x)TeO₂–xBaO, with x = 05, 10, 15 and 20 wt%, have been prepared and studied by differential scanning calorimetry (DSC). The crystallization kinetics of the glasses were investigated under non-isothermal conditions, applying the formal theory of transformations for heterogeneous nucleation to the experimental data obtained by DSC, using continuous-heating techniques. In addition, from the dependence of the glass-transition temperature (T _g) on heating rate, the activation energy for the glass transition was derived. Similarly, the activation energy of the crystallization process was determined and the crystallization mechanism characterized. The thermal stability of these glasses are considered in terms of the characteristic temperatures, T _g and T _in (the onset temperature of crystallization), via ΔT = T _in?T _g and a kinetic parameter K(T _g). The results confirm that thermal stability decreases with increasing BaO content. The phases into which the glass crystallizes have been identified by X-ray diffraction. Diffractograms of the transformed material indicate the presence of microcrystallites of α-TeO₂, γ-TeO₂ and BaTeO₃ in the remaining amorphous matrix.     

Inorganic phosphors in lead–silicate glass for white LEDs

Using spectrophotometry and stationary and kinetic fluorimetry, we have shown that xanthene dye fluorescein forms complexes with polycationic derivative of fullerene in aqueous solutions mainly due to electrostatic interactions. It is found that efficient quenching of singlet excited states of dye occurs in the structure of these complexes due to the transfer of excitation or electron from dye to fullerene. As a result, the photodynamic activity of the newly formed complex is much higher than that of fluorescein and fullerene derivative. This effect makes it possible to predict the formation of new-generation hybrid photodynamic preparations using dyes excited only into a singlet state; as a result, directed searches for these dyes are significantly facilitated.     

Absorption and emission properties of Bi-doped Mg–Al–Si oxide glass system

A new Bi-doped Mg–Al–silicate glass is suggested and investigated. It can be fabricated by moderate-temperature routine technology. The characteristic relaxation time of 300–800 μs in combination with the high quantum yield (up to 85%) and wide excitation spectrum makes this glass a promising laser material. The obtained quadratic dependence of the visible absorption intensity is an argument in favor of the hypothesis that the absorption and infrared luminescence in Bi-doped glasses are caused by Bi₂ dimers.     

Optical properties of Au–Ag core–shell nanorods on glass and ITO substrates

Gold-silver core–shell nanorods were deposited on glass and ITO plates. SEM observations indicated that some of these nanorods were standing on the ITO plate. The extinction spectra of the plates were measured by varying the angles of incidence of p-polarized monitor light. Deconvolution of these spectra gave six bands in the visible region. The dependence of the peak intensities on the incident angles indicated that the bands at 390 and 420 nm originated from surface plasmon bands in the transverse direction of the nanorods.     

Medium range ordering and its effect on plasticity of Fe–Mn–B–Y–Nb bulk metallic glass

Glass formation, thermal properties and mechanical behavior were investigated in a series of Fe_{65? x} Mn₁₃B₁₇Y₅Nb _x (x = 0, 3, 5 and 7) alloys. Appropriate partial substitution of Fe by Nb in a Fe₆₅Mn₁₃B₁₇Y₅ bulk glassy alloy simultaneously enhances the glass-forming ability and the mechanical properties of the alloys. The Nb-containing glassy alloys exhibit an additional exothermic event in the supercooled liquid region. This exothermic reaction is correlated with the formation of medium range ordered (MRO) clusters originated from the large difference in mixing enthalpy between constituent elements such as Nb–Y (+30 kJ/mol) and Nb–B (?39 kJ/mol). The presence of MRO clusters in the as-cast state is dependent on the cooling condition from the liquid state, and plays a crucial role in providing plasticity in as-cast Fe–Mn–B–Y–Nb bulk metallic glass.     

Influence of environment on the corrosion of glass–metal connections

‘Glass sensors’ of the eighteenth century Backer glass and the sixteenth century enamel from Limoges have been chosen for a series of experiments. Combinations of these materials with different base materials such as copper and bronze has been investigated. To create surface changes on the ‘glass sensor’, a corrosion process was induced in a controlled environment. A variety of corrosive agents such as hydrochloric acid, sulfuric acid, water and formaldehyde were used. The sample immersed in the corrosive solution was exposed alternately to light and high temperature for a total of 38 weeks. During this period, macroscopic and microscopic observations were made and series of tests such as SEM/EDS and Raman spectroscopy were performed on the surface of the samples. ICP-MS methods were used to determine the change in the chemical composition of the solutions where the samples had corroded. The primary aim of this study was to identify the impact of a number of external corrosive variables such as temperature, humidity and local environment to identify the most damaging environments for glass–metal objects. The obtained results showed the chemical and physical phenomena acting on the surface of the glass, metal or in the place of their joints. Information obtained on this study was used to explain the influence of the environment on the surface of glass–metal materials. Results can be used in the design of conservation work as well as for sustainable conservation.     

High temperature strain glass in Ti–Au and Ti–Pt based shape memory alloys

Strain glass is a frozen short-range strain ordered state found in shape memory alloys recently, which exhibits novel properties around the ideal glass transition temperature T₀. However, the T₀ of current strain glass systems is still very low, limiting their potential applications and experimental studies. In this paper, we reported two new strain glass systems with relatively high T₀. In Ti₅₀Au_50-xCr_x alloys, the strain glass appears at x = 25, and exhibits a T₀ of 251 K, while in Ti₅₀Pt_50-yFey alloys, the strain glass takes place at y = 30, and shows a T₀ of 272 K. Both of them are comparable with the highest T₀ value reported so far. Moreover, the phase diagrams of main strain glass systems in Ti-based alloys were summarized. It is found that the influence of the martensitic transformation temperature of the host alloy on the T₀ of the strain glass is limited. This work may help to design new strain glass systems with higher T₀ above ambient temperature.     

High pressure luminescence study of Sm3+: K–Ba–Al fluorophosphate glass

The luminescence spectra and decay curves for the ⁴G_5/2 level of Sm³⁺ ions in 55.95P₂O₅+14K₂O+6KF+14.95BaO+9Al₂O₃+0.1Sm₂O₃ glass, referred to as PKFBASm01, have been studied as a function of pressure up to 40.5 GPa at room temperature. With the increase in pressure, a continuous red shift of the ⁴G_5/2→⁶H_{9/2, 7/2, 5/2} transitions and a progressive increase in the magnitude of the crystal-field splittings for these transitions are observed. The decay curves for the ⁴G_5/2 level of the Sm³⁺ ions in PKFBASm01 glass are found to exhibit single exponential behavior at ambient pressure and become non-exponential at higher pressures, accompanied by shortening of lifetimes. A generalized Yokoto–Tanimoto model has been used to explain the pressure-induced non-exponential nature of the decay curves.     

Er–Pr doped tellurite glass nanocomposites for white light emitting diodes

In this paper, optical glass nanocomposites (nanoparticles sizes up to 100 nm) with composition TeO₂–WO₃–PbO–xEr₂O₃–yPr₆O₁₁ (x = 0.30 mol%, y = 0.70 mol%) embedded into polymer matrices was reported. The two types of polymers chosen for present study were: photopolymer oligoetheracryalte (OEA) and polymethylmethacrylate (PMMA), respectively. The incorporation of the titled nanoparticles into the polymer matrices is analyzed optically. The fluorescence spectra of the nanocomposites were compared with the fluorescence spectra of bulk glasses. Based on the comparison of Er^3 + and Pr^3 + ions' energy level schemes, possible energy transfer processes were identified. The prepared glasses are promising candidates for the white light emitting diodes applications.     

Effects of Re microalloying on glass formation and mechanical properties of Zr–Cu–Al alloys

The effect of microalloying with rhenium on a metallic glass-forming alloy (Cu₄₆Zr₄₆Al₈)_{100? x} Re _x (x?=?1,?2) was investigated. Re possesses a positive enthalpy of mixing within the Cu–Re terminal system. Splat quenched foils of ≈40?µm in thickness display an amorphous structure. Their crystallisation temperature increases from T _x?=?504 to 513°C with addition of Re at nearly constant glass formation temperature T _g?=?445°C for the amorphous samples. In contrast, injection cast rods consist of B2-CuZr type phase dendrites, minor fractions of a cubic phase CuZrAl, and randomly distributed small particles of a Re-rich phase. This represents a novel concept in microalloying where Re-rich precipitates trigger the B2 phase formation. It leads to a unique combination of mechanical properties for as-cast rods, which display high strength at sizeable plastic deformation up to ε _p?≈?4% and an extended range of work-hardening prior to failure.     

Ultrafast non-resonant third-order optical nonlinearity of GeS2–Ga2S3–CdS chalcogenide glass

Ultrafast third-order nonlinear optical responses of 4(1?x)/5GeS₂-(1?x)/5Ga₂S₃-xCdS (x=0.05, 0.10 and 0.15 in mol%) chalcogenide glasses was investigated by using the femtosecond time-resolved optical Kerr effect technique at a wavelength of 800 nm. The largest third-order nonlinear susceptibility of all samples was estimated to be 1.65×10^?13 esu. An ultrafast nonlinear response time of about 250 fs was observed, which was dominantly assigned to the ultrafast distortion of the electron cloud under femtosecond laser excitation. A nonlinear relationship between the third-order nonlinear susceptibility and the introduced amount of CdS was discussed, suggesting a possible disturbance between different polarizable bonds in the glass system.     

High glass formability for Cu–Hf–Ti alloys with small additions of Y and Si

The effects of small substitutions of Si and Y on the glass-forming ability of a Cu₅₅Hf₂₅Ti₂₀ glassy alloy are reported and discussed. Fully glassy rods with diameters up to 7 and 6.5 mm were produced for Cu_54.5Hf₂₅Ti₂₀Si_0.5 and Cu_{55? x} Hf₂₅Ti₂₀Y_0.3 alloys, respectively. The addition of Si enlarged ΔT_x (= T_x ? T _g, where T _g and T_x are crystallisation and glass transition temperatures, respectively) considerably, from 25 to 53 K for the Cu₅₄Hf₂₅Ti₂₀Si₁ alloy. However, the results showed that the parameters obtained from thermal analysis, such as T _rg , ΔT_x and γ[= T_x /(T _g + T _l)] are not reliably correlated with the glass-forming ability (GFA), at least for these bulk glass-forming alloys. The scavenging effects of the Y and Si, in particular the possibility of Y reducing the oxides, could be responsible for enhancing the GFA. It is proposed that the effectiveness of small additions of Si in enhancing the GFA may be the result of the possible formation of HfSiO₄ having a very large negative enthalpy of formation and, as a strong network former, it would form glassy particles which would be ineffective as nucleating agents.     

Large-scale interfacial damage and residual stresses in a glass–ceramic matrix composite

The current work is concerned with the micro-mechanics of fracture of a SiC-fiber-reinforced barium osumilite (BMAS) ceramic matrix composite tested under both monotonic and cyclic tension. The double-edge notch (DEN) specimen configuration was employed in order to confine material damage within a predefined gage length. The imposition of successive loops of unloading to complete load relaxation and subsequent reloading were found to result in an increase by 20% in material strength as compared to pure tension; the finding is attributed to energy dissipation from large-scale interfacial debonding phenomena that dominated the post-elastic mechanical behavior of the composite. Cyclic loading also helped establish the axial residual stress state of the fibers in the composite, of tensile nature, via a well-defined common intersection point of unloading–reloading cycles. An approach consisting of the application of a translation vector in the stress–strain plane was successfully used to derive the residual stress-free properties of the composite and reconcile the scatter noted in elastic properties of specimens with respect to theoretical expectations.