The glass transition of Pd40Ni10Cu30P20 studied by temperature-modulated calorimetry

The frequency dependence of the heat capacity in the glass-transition region of Pd₄₀Ni₁₀Cu₃₀P₂₀ was studied by temperature-modulated differential scanning calorimetry (TMDSC) during slow heating and cooling. Such data for low frequencies between 0.1 and 0.01 Hz are not available, especially for metallic glasses. A crossover between mixed static/dynamic and purely dynamic response signals was observed for the lowest frequencies between 1/80 and 1/100 s⁻¹, which allows a direct determination of the average relaxation time at a given cooling rate during the static glass transition. Further, these results were used to evaluate the experimental parameters necessary to truly separate the static and dynamic response in low-frequency modulation calorimetry experiments to obtain the moduli of the dynamic specific heat.     

Glass formation in the PbBr2–PbCl2–PbF2–PbO–P2O5 system

New glasses in the PbBr₂–PbCl₂–PbF₂–PbO–P₂O₅ system have been prepared and characterized. The glass-forming regions have been explored and the stability of the glasses against crystallization studied. Results show that the PbBr₂–PbCl₂–P₂O₅ ternary system has a broad glass-forming region which extends to 30 mol% P₂O₅. Most of the glasses in this system show strong stability against crystallization and some have glass transition temperatures as low as 146°C. When 5% PbO or 5% PbF₂ is introduced into the PbBr₂–PbCl₂–P₂O₅ system, the glass-forming region becomes smaller and the glass transition temperatures increase. However, the introduction of 2.5% PbF₂ and 2.5% PbO into the ternary system increases the glass transition temperature and broadens the glass-forming region. The introduction of PbF₂ alone improves the glass-forming ability of the system while the introduction of PbO alone lowers the glass-forming ability.     

Thermally modulated differential scanning calorimetry of a glass of composition 45Na2O-40B2O3-10Al2O3-5In2O3

The kinetics of structural relaxation and of glass transition of the 45Na₂O-40B₂O₃-10Al₂O₃-5In₂O₃ glassforming melt is studied by means of standard DSC and of temperature modulated DSC. In this way the dependence of the fictive temperature on cooling rate is determined simultaneously with the determination of the dependence of the dynamic glass transition temperature on modulation frequency. Both sets of data are fitted together in terms of the equation of Ritland-Bartenev. It was found that the activation energy of the structural relaxation exhibits a moderate dependence on temperature with the dimensionless fragility parameter α=3.3 (for strong systems, α is about 1 and increases to about 8 for some very fragile polymeric systems).     

On the dependence of the properties of glasses on cooling and heating rates: I. Entropy, entropy production, and glass transition temperature

The glass transition is theoretically described in terms of a generic non-equilibrium thermodynamics approach employing De Donder's structural order parameter method, appropriate expressions for the relaxation behavior of glass-forming systems and a simplified but qualitative correct model of glass-forming melts with one order parameter related to the free volume of the system. Employing this approach the behavior of a variety of thermodynamic quantities describing glass-forming systems in vitrification and devitrification processes is interpreted theoretically. The present paper is devoted to the computation of the entropy, the entropy production and the glass transition temperature in dependence on the cooling and heating rates, varying latter parameter in a broad interval. A comparison with experimental results is given and some further consequences and possible extensions are discussed briefly.     

The observation of two glass transitions in the dynamic mechanical properties of a La55Al25Ni20 amorphous alloy

The glass transition behavior of a La₅₅Al₂₅Ni₂₀ amorphous alloy was examined through the changes in the storage, E′, and loss, E″, moduli obtained by a forced oscillation method. Two distinguishable relaxation peaks are observed in the glass transition region, although these are not resolved in calorimetric measurements. At a frequency of 62.8 rad/s, E″ shows two peaks at 483 and 507 K. As the frequency decreases, the splitting of the two peaks becomes distinct and their peak temperatures shift to a lower value. The change in E″ with frequency also shows the two relaxation peaks. A master curve of E″ is derived by using the time-temperature superposition process. This is the first master curve for the relaxation spectrum in the glass transition region for amorphous alloys. The activation energies evaluated from the shift factors are 400 and 550 kJ/mol for the lower and higher temperature peaks, respectively.     

Structure and properties of Bi2O3---BaO---CuO glasses

The glass-forming region in the BiO_1.5---BaO---CuO system was determined, and the structure and crystallization of the glasses were investigated and compared to glasses containing CaO or SrO in place of BaO. It has been found that the glass-forming region in this system is wider than those in the BiO_1.5---CaO---CuO and BiO_1.5---SrO---CuO systems. BaBiO_2.77 was preferentially formed in the first stage of crystallization at all glass compositions. It is suggested that the Ba²⁺ ions may preferentially occupy the sites near BiO₆ octahedra, while the Ca²⁺ ions in BiO_1.5---CaO---CuO glasses may not have a site preference with respect to the BiO₆ octahedra.     

Viscosity of (GeSe2)x(Sb2Se3)1−x undercooled melts

Viscosity of (GeSe₂)_x(Sb₂Se₃)_1−x undercooled melts (x = 0.4-0.8) was measured using parallel-plate method and penetration method. By using these two techniques viscosity of the whole measurable region of undercooled melt and of the part of glass region can be measured. In this relatively broad viscosity interval (seven orders of magnitude) all measured samples show Newtonian behavior and the dependence of their viscosity on temperature can be described by a simple Arrhenius equation. The kinetic fragilities calculated from these dependencies show similar compositional dependence as heat capacity changes at glass transition measured by DSC.     

Glass formation and optical properties of glasses in the systems (R2O or R''O)-Ta2O5---Ga2O3

Gallate glasses containing no conventional glass formers were obtained in the systems (Na₂O, K₂O or Cs₂O)-Ta₂O₅---Ga₂O₃ and (Sr or BaO)-Ta₂O₅---Ga₂O₃ by an ordinary crucible-melting technique. The glasses showed high optical transmission in the infrared as well as in the visible region. Infrared spectroscopic analysis suggested that the Ga³⁺ ions are tetrahedrally coordinated in the glasses. The glass-forming tendency of the melt and the infrared transmission of the glasses are discussed in terms of the glass structure.     

Evaluation of glass-forming ability criterion from phase-transformation kinetics

Applying kinetic analysis upon crystallization of metallic glass, a quantitative relation between the critical cooling rate and the onset temperature of crystallization was obtained for glass-forming alloys. Effects of the onset temperature of crystallization, the liquidus temperature and the glass transition temperature on the critical cooling rate were analytically described. Three rules guiding the development of more reliable glass-forming ability criteria are suggested.     

Thermodynamic and thermokinetic characteristics of the glass transition in a GeSe2GeTeSb2Te3 alloy

Glassy alloys of (GeSe₂)₇₀ (GeTe)₁₅ (Sb₂Te₃)₁₅ were prepared by water-quenching and subjected to several thermal treatments through the glass transition region. The thermodynamic and thermokinetic characteristics of the glass were inferred from heat capacity measurements by differential scanning calorimetry. It was demonstrated that the undercooled liquid obtained by heating the glass is in equilibrium, and what is more, that not only each particular cooling process through the glass transition produces a given glass, but also that any trance of the glass may be suppressed by reheating above glass transition. The enthalpy and entropy differences between each glass and the undercooled liquid used to obtain that particular glass were taken as properties sensitive to the relaxation inherent to the formation of the glass. The activation energy spectrum characterizing the relaxation processes on cooling through the glass transition has been obtained. It has a peak energy of 1.43 eV which may be related to the bonds between the constituent atoms of the sample with weaker interaction energy. Therefore, the relaxation may be due to a breaking and rearrangement of these bonds in the glassy structure.     

Ionic conduction in As2S3---Ag2S, GeS2---GeS---Ag2S and P2S5---Ag2S glasses

The glass-forming region in the system P---S---Ag was determined and density, thermal expansion, dc conductivity and the transport number of Ag ions were measured for P₂S₅---Ag₂S glasses found in the P---S---Ag system. The results for the transport number measurement show that P₂S₅---Ag₂S glasses are purely ionic conductors owing to the Ag ion migration, like most of the As₂S₃---Ag₂S and GeS₂---GeS---Ag₂S glasses reported previously. Glass structure and ionic conduction processes in As₂S₃---Ag₂S, GeS₂---GeS---Ag₂S and P₂S₅---Ag₂S glasses are discussed, based on their ionic conductivity and density data. The structural concept of -Ag₂S was applied to these glasses, which suggests that the Ag ions in the glasses are distributed in the available Ag ion sites in the non-conducting framework composed of both S anions and As, Ge or P cations. In each system the ionic conductivity increases linearly with increasing Ag⁺/total cation (%) in glass composition, the determining factor being the activation energy for ionic conduction alone. Thus, the activation energy in these glasses depends predominantly upon the molar ratio of Ag ions to total cation in the glass, irrespective of the kind of system. Small differences in the activation energy among the three systems can be interpreted as arising from differences in the field strength of As, Ge and P cations.     

Glass formation, properties and structure of glasses in the P2O5---WO3---K2O---Al2O3 system

Glass formation in the P₂O₅---WO₃---K₂O---Al₂O₃ system was investigated and the glass-forming regions are presented.

the properties of the glasses in the P₂O₅---WO₃---K₂O---Al₂O₃ system (Al₂O₃ 8 mol.%) are reported.

The colouration of glass was studied. It was found that W⁵⁺ ions make glass blue.

Infrared spectra were measured by means of making KBr pills. Results of the investigation suggest that P---O---P, P---O---W, and W---O---W bonds form a continuous network in the phosphate glasses. So we suggest that tungsten trioxide is a glass former.     

Characterisation of semiconducting V2O5–Bi2O3–TeO2 glasses through ultrasonic measurements

Tellurite containing vanadate (50−x)V₂O₅–xBi₂O₃–50TeO₂ glasses with different bismuth (x=0, 5, 10, 15, 20 and 25 wt%) contents have been prepared by rapid quenching method. Ultrasonic velocities (both longitudinal and shear) and attenuation (for longitudinal waves only) measurements have been made using a transducer operated at the fundamental frequency of 5 MHz in the temperature range from 150 to 480 K. The elastic moduli, Debye temperature, and Poisson’s ratio have been obtained both as a function of temperature and Bi₂O₃ content. The room temperature study on ultrasonic velocities, attenuation, elastic moduli, Poisson’s ratio, Debye temperature and glass transition temperature show the absence of any anomalies with addition of Bi₂O₃ content. The observed results confirm that the addition of Bi₂O₃ modifier changes the rigid formula character of TeO₂ to a matrix of regular TeO₃ and ionic behaviour bonds (NBOs). A monotonic decrease in velocities and elastic moduli, and an increase in attenuation and acoustic loss as a function of temperature in all the glass samples reveal the loose packing structure, which is attributed to the instability of TeO₄ trigonal bipyramid units in the network as temperature increases. It is also inferred that the glasses with low Bi₂O₃ content are more stable than with high Bi₂O₃ content.     

X-ray diffraction measurements for liquid As2Se3 up to the semiconductor-metal transition region

X-ray diffraction measurements were performed for liquid (1-) As₂Se₃ at temperatures and pressures up to 1500°C and 70 bar. A high-pressure vessel and a sapphire sample cell were developed, according to the authors' own design, for measurements using the energy-dispersive method. The structure factor becomes broadened with increasing temperature and changes significantly at about 1000°C accompanied by the semiconductor-to-metal (SC-M) transition; the first sharp diffraction peak around 1.2Å⁻¹ disappears and the second and third maxima merge. The nearest-neighbor distance and the average coordination number start to increase when the SC-M transition occurs. The density of 1-As₂Se₃ in the temperature and pressure range up to 1600°C and 700 bar, respectively, were also measured by the X-ray absorption method. A volume contraction occurs in the SC-M transition region.     

Dynamical scaling analysis using the Lillie Number for vitrification of deeply supercooled glycerol

Thermal response was measured for a deeply supercooled glycerol specimen by applying calorimetric temperature scanning rate spectroscopy, cooling the specimen from liquid at a slow constant cooling rate until glass transition was observed. The effective fraction of glass as a function of temperature was determined and a new definition of glass transition temperature, T_gC, as the temperature at which the effective glass fraction to be 0.5 was presented. The relation between this and the cooling rate showed the Arrhenius behavior. The effective glass fraction curves shifted linearly as a function of ln(cooling rate). When T was scaled to the Lillie Number, the glass fraction lay on a master curve, which was successfully fitted with a Kohlrausch–Williams–Watts function. The Kohlrausch exponent, the relaxation time as a function of temperature and the kinetic fragility index were determined. The results were compared with literature values.     

Single-crystal growth of sulphospinel CuIr2S4 from Bi solution

Single crystals of a sulphospinel CuIr₂S₄ have been grown from bismuth solution by a slow cooling method for the first time. The grown crystals have a maximum edge of about 1 mm in size and a mirror-like shining surface. Optimum growth conditions are fairly strict. The specific weight of starting materials for the crystal growth is found to be 0.30 g of CuIr₂S₄ and 10.0 g of Bi in order to obtain good quality crystals. The starting and finishing temperatures for the slow cooling step in the temperature control are 1000 and 500°C. The pertinent cooling rate is 2°C/h. Since the volume of bismuth itself expands in the transition from liquid phase to solid phase, a simple method of separation of the grown crystals from the liquid solution will be proposed for avoiding the mechanical damages to the grown crystals. The single crystals have the normal-spinel structure of the lattice constant a=9.849 Å at room temperature. A step-like anomaly in the susceptibility of the single crystals, corresponding to the metal–insulator transition in the resistivity, occurs much sharply than in the powder specimen.     

On the glass transition in vitreous silica by differential thermal analysis measurements

Scanning calorimetry measurements of the glass transition in vitreous SiO₂ (about 120 wt ppm. OH groups) are reported. Data were obtained upon heating after controlled cooling through the glass transition, and after annealing at temperatures between 990 and 1292 K. The onset of the glass transition is at 1247 K, and the supercooled liquid state is reached at 1475 K. The step in the specific heat is (2.9 ± 0.7) J mol⁻¹ K⁻¹. This value, lower than the results of drop calorimetry experiments, agrees with the calculated value from viscosity data. The glass transition is nearly twice as wide as expected from the temperature dependence of the viscosity. Annealing reduces the enthalpy of glasses as usually expected, and the corresponding entropy decrease is in agreement with results for other network glasses. In vitreous silica, depending on the annealing temperature, both exothermic and endothermic processes take place. Based on Davis’ and Tomozawa’s results, endothermic processes upon annealing are attributed to the diffusion of the OH groups.     

Glass formation and crystallization in the ZrO2---Al2O3---P2O5 system

The glass formation of the ZrO₂---Al₂O₃---P₂O₅ system in the high phosphate region is determined. The crystallization process and the crystal types formed during heat treatment have been studied. The structure of these glasses is discussed.     

Kinetics of vitrification under electric fields

The influence of electric fields on the kinetics of vitrification was considered using the formalism of the thermodynamics of irreversible processes and the model of the activated complex. Expressions for the dependence of the glass transition temperature on cooling rate (under constant electric fields) and for the field strength at which the system vitrifies on the rate of change of field strength (at constant temperature) were derived. It was shown that, in general, the glass transition temperature is lowered when an electric field is applied to an undercooled melt. The formalism derived can be used to describe vitrification kinetics when the liquid is subjected to magnetic fields.