Low-frequency internal friction of metallic glasses near Tg A critique of the use of the torsion pendulum

The application of the torsion pendulum to internal friction measurements on metallic glasses near the glass transition is critically analysed. It is pointed out that a difference between the measured damping Q_t⁻¹ and the real internal friction Q_s⁻¹ of the mterial must be taken into account; quantitative expression are given for the inverted and Collette types of torsion pendulum. The Collette pendulum is found particularly useful for measuring the internal friction of metallic glasses during slow heating through the glass transition. The results obtained with this instrument on six different Pd- and Ni-based glasses, as well as theoretical evidence, suggest that the extremely large internal friction “peak” above T_g is generally due to the intervention of crystallization after a large eand monotonous increase of viscoelastic damping in the supercooled liquid. In particular, there is no vidence for a real internal friction peak due to the glass transition. This conclusion is contradictory to some internal friction results found in the literature which have been obtained with a conventional inverted torsion pendulum. For this type of pendulum, the difference between Q_t⁻¹ and Q_s⁻¹ has obviously not been sufficiently tajen into account.     

Physical properties of glasses containing several glass-forming oxides

Physical properties, such as dielectric loss, acoustic velocity and electrical conductivity of glasses containing several glass-forming oxides were measured at temperatures in the range from −200°C to 200°C. The relationships between the structure and properties of the glasses, and the change in coordination number of individual glass-forming cations in alkali-containing glasses were analysed. It is shown that the glasses containing several glass-forming oxides are characterized by an inhomogeneous structure.     

RDF analysis, positron annihilation and Raman spectroscopy of xTiO2-(60 − x)SiO2-40Na2O non-linear optical glasses: III. Non-bridging oxygen bonds tracing and structure analysis

xTiO₂-(60 − x)SiO₂-40Na₂O glasses have proven an interesting linear and non-linear optical properties [M. Abdel-Baki, F. Abdel Wahab, F. El-Diasty, Mater. Chem. Phys. 96 (2006) 201]. The investigated glasses show one order of magnitude enhancement for the second-order index of refraction and third-order optical susceptibility over some TiO₂ silicate glasses. In this work, we continue studying these glasses using three different techniques to analyze the glass structures seeking to provide a deep insight for the relation between structure, compositions and the optical characteristics of these glasses. Radial Distribution Function analysis (RDF) combined Raman spectroscopy are used to study these glasses. Positron annihilation lifetime spectroscopy and Doppler broadening measurements are carried out to investigate the change in the glass structure as the incorporation of TiO₂ concentration into glass. The origin of the non-bridging oxygen (NBO) bonds has been traced to correlate their existence with the measured non-linear optical properties of the investigated glasses.     

Internal friction in vanadium-phosphate glasses doped with Na2O

The internal friction of _xNa₂O·(0.5−x)V₂O₅·O.5P₂O₅(x = 0.025–0.3) glasses was studied using the low-frequency torsion pendulum technique. The temperature spectrum of internal friction reveals three maxima. Maximum 1, the so-called “electron” maximum, is the same as observed in binary vanadium-phosphate glasses. The origin of maximum 2 can be attributed to ion migration. Maximum 3 appears for glasses containing more than 10 mol.% Na₂O and is probably connected with sodium-proton interactions.     

The mixed alkali effect in sodium and potassium galliosilicate glasses II. DC electrical conductivity

The DC electrical conductivities of several series of mixed alkali galliosilicate glasses have been measured. The appearance of a minimum in the electrical conductivity of these glasses, independent of the gallium content, suggests that the mixed alkali effect is independent of the non-bridging oxygen content. These results are discussed in terms of current theories proposed to explain this anomalous behaviour.     

Vibrational spectra and structure of chloro-fluorozirconate glasses

A series of barium chloro-fluorozirconate glasses have been prepared. Their IR absorption, IR reflectivity and Raman spectra have been measured down to 33 cm^?1. The glass transition and crystallization temperatures have also been measured. The high frequency IR absorption and Raman modes of the chloro-fluorozirconate glasses have been assigned as in fluorozirconate glasses. The IR reflection spectra of chloride-containing glasses differed from the fluorozirconates in that one band was clearly related to Cl atom motions. The structure of the glasses probably consists of zig-zag chains of ZrCl₂F₄ mixed halide octahedra plus a pure fluoride matrix whose structure is similar to that of a ZrF₄BaF₂ glass with the same composition.     

Crystallization of glasses in the germanium-tellurium-sulphur system

The glasses of the germanium-tellurium-sulphur ternary system were investigated in order to determine the formation and crystallization processes. Vitreous samples were prepared by quenching. The vitreous transition and crystallization temperatures, together with microhardnesses, were measured throughout the vitreous region. The latter was sub-divided into several zones, and the behaviour of the glasses in each of these zones was analyzed separately.     

Physical properties of phase separated soda-silica glasses

Changes in the physical properties of several soda-silica glasses, caused by amorphous phase separation, have been measured. This includes denisty, thermal expansion, and Young's modulus. The results correlate with a continuously changing microstructure including partial crystallization. The transition range behavior of a phase separated glass differs only slightly from a homogeneous glass of the same composition.     

Internal friction of mixed alkali metaphosphate glasses: (I). Results

The internal friction of LiNa, LiK, LiCs, LiAg, NaCs and NaAg metaphosphate glasses was measured at 0.5 Hz and 2 kHz. The dielectric losses were also measured from 40 to 160°C, at frequencies of 300, 3 000 and 30 000 Hz. The densities of the glasses were determined and the molar volume of oxygen was calculated. In general, the mixed alkali behaviour of metaphosphate glasses is very similar to the mixed alkali behaviour of silicate glasses. Silver behaves in this respect like an alkali ion with approximately the same size as a sodium ion.     

The spectroscopic behavior of high CaO content,laser-type glasses

Spectroscopic measurements were made of three high CaO content Nd³⁺-doped glasses, two of which could only be prepared via splat cooling. Cross-section determinations of the Nd³⁺ 1.06 μm lasting line were performed for each of these glasses via several methods. The use of absorption spectroscopy and the Judd-Ofelt crystal field calculations indicated that the lasting line cross-section, viewed as a function of CaO content in these glasses, possesses a maximum. Fluorescent decay-time measurements, however, suggested a monotonically increasing cross-section with increasing CaO concentration in the base glass composition. Non-radiative decay processes could be responsible for the discrepancy in these results.     

Indentation response of glass with temperature

The mechanical response of different glasses to a Vickers indentor has been investigated between room temperature and T_g+50 °C. The permanent deformation, from which hardness is estimated, as well as the brittle fracture characteristics, allowing for an evaluation of the fracture toughness, were measured and analysed. Comparison between a standard float glass and advanced glasses such as chalcogenide (with mainly covalent bonding) and metallic glasses was made to get a more general insight into high temperature indentation behaviour. As temperature increases, the glass response becomes more and more time-dependent, and in the vicinity of T_g the permanent deformation was observed to increase rapidly for all glasses. Further, while the standard float glass showed an enhanced apparent toughness at elevated temperatures due to a brittle to ductile transition, almost no change in apparent toughness was revealed in the GeAsSe glass emphasizing the time-dependent response of glass at elevated temperature.     

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.     

Direct calculation of Young's moidulus of glass

An equation has been derived for the direct calculation of the Young's modulus of oxide glasses from their chemical compositions. The method is based on a consideration of dissociation energy of the oxide constituents per unit volume and the packing density. For borate glasses, the ratio of four-coordinated to three-coordinated borons must be taken into consideration. Excellent agreement is obtained between calculated and measured values of Young's modulus for over thirty different glasses.     

Glass microstructure evaluations using high temperature mechanical spectroscopy measurements

This paper compares the microstructures of several glasses by measuring the Young’s modulus and internal friction as a function of temperature, using the impulse excitation technique (IET). IET is based on the analysis of the resonant vibration of a solid material sample, induced by an impulse excitation. IET determines the mechanical resonant frequencies (f_r) from which the elastic moduli can be calculated, and for each f_r the corresponding internal friction (Q⁻¹). It was found that the stiffness of quartz and borosilicate glasses increases with temperature. The stiffness of soda-lime and alumino-silicate glasses decreases with the increase of temperature. The change of stiffness of quartz and alumino-silicate glasses during heat-treatment is reversible, but that of borosilicate and soda-lime glasses is not. Explanations for the irreversibility are suggested based on the Q⁻¹-features of the glasses. Diffusion of network modifier ions in the glass network holes is proposed to cause a non-reversible stiffness change, whereas localised anelastic relaxation of network modifier ions leads to a reversible stiffness change.     

The vibrational spectra of B2O3-GeO2 glasses

Infrared and Raman spectra were measured for a series of glass compositions in the binary B₂O₃-GeO₂ system at room and elevated temperatures. No coordination changes were detected from spectral analysis for either boron or germanium with concentration or temperature changes. Interpretation of the vibrational spectra indicated that both boroxol rings and BO₃-triangular units were present as the basic units in glasses with higher B₂O₃ concentrations. Only BO₃-triangular units were detected as the basic units in glasses with lower B₂O₃ concentrations. Raman spectra of glasses measured at higher temperatures (>T_g) indicated that their boroxol ring concentrations decreased as a function of temperature. The enthalpy for ring rupture in 35GeO₂–65B₂O₃ glass was 7.7 kcal/mol. Also, spectral analysis indicated that the boroxol ring concentrations of these glasses at room temperature were dependent upon their previous heat treatments.     

The thermal conductivity of some chalcogenide glasses

The temperature-dependent thermal conductivities of several chalcogenide glasses were determined above 300 K. At 300 K, the thermal conductivity for most of these glasses is about 3 mW/cm · deg.     

Electrical transport in n-type semiconducting Ge120BixSe70−xTe10 glasses

Resistivity and thermoelectric power were measured as a function of temperature and composition for Ge₂₀Bi_xSe_70?xTe₁₀ glasses (x = 0–11). The results were compared with the case of of Ge₂₀Bi_xSe_80?x glasses to see on the electrical properties the influence of the substitution of Te for a part of Se. The glasses show n-type conduction for x ? 9, which was not affected by the substitution of Te. The resistivity was about three orders of magnitude lower for the glasses with x < 10, and remained almost the same for x ? 10, compared with the glasses not containing Te. From the composition dependence of the calculated concentration of covalent bonds in the glasses, it was proposed that the appearance of n-type conduction was closely related to the formation of a sufficient number of BiSe bonds and the disappearance of the bonds between two chalcogen atoms such as TeSe or SeSe bonds, and that the remarkably low resistivity in the present glasses with x < 10 was likely to be attributed to the formation of TeSe bonds.     

Structural investigation of SnO-B2O3 glasses by solid-state NMR and X-ray photoelectron spectroscopy

Local structure of the SnO-B₂O₃ glasses was investigated using several spectroscopic techniques. ¹¹B MAS-NMR spectra suggested that BO₄ tetrahedral units maximized at around the composition with 50 mol% SnO. The BO₄ units were still present at compositions with high SnO content (67 mol% SnO), suggesting that SnO acted not only as a network modifier but also as a network former. O1s photoelectron spectra revealed that the addition of small amounts of SnO formed non-bridging oxygens (NBO) (B-O?Sn) and the amounts of NBO increased with an increase in SnO content. ¹¹⁹Sn Mössbauer spectra indicated that Sn was present only as Sn(II) in the glasses. The structure of the SnO-B₂O₃ glasses was compared with that of conventional alkali borate glasses and lead borate glasses. The thermal and viscous properties of these glasses were discussed on the basis of the glass structure revealed in the present study.     

Inelastic neutron and low-frequency Raman scattering in a niobium-phosphate glass for Raman gain applications

We present measurements of the vibrational spectrum of a binary niobium-phosphate glass in the THz frequency range using inelastic neutron and Raman scattering. The spectra of these glasses show a low-frequency enhancement of the vibrational density of states (“boson peak”). Using a recently developed theory of vibrational excitations in disordered solids we are able to reconcile the measured neutron and Raman spectra using fluctuating elastic and Pockels constants as a model concept. As the spontaneous Raman susceptibility is a key parameter for Raman amplification our results suggest a significant gain profile for application of niobium-phosphate glasses in Raman amplifiers.     

Study of PbO films on sodium borate glasses part II: Formation of interdiffusion layers at the glass surface

By selecting carefully controlled conditions for the thermal treatment of sodium borate glasses coated with PbO films, it is possible to prevent Pb²⁺ ions from penetrating deeply into the glass. For low alkali glasses, an interdiffusion layer can be formed, which sub-surface cation profiling (by ion beam induced radiation) shows is a solid solution of Na₂O and B₂O₃ in PbO which acts as solvent. Experiments with 18.0 mol-% Na₂O glass show that it is possible to transform such an interdiffusion layer into a second type in which Na₂O and B₂O₃ together act as solvent and the concentration of PbO solute varies through the layer. For both types of layer the Na₂O : B₂O₃ ratio is different from that of the glass substrate, and for the production of the second type of layer it is shown that an important factor connected with penetration of PbO into the glass surface is a “sweating” process in which thermal treatment of the glass, even in the absence of PbO, results in migration of Na⁺ ions so that the glass surface has a Na₂O content higher than that of the bulk glass. Changes in the UV spectra of the Pb²⁺ ion are correlated with the formation of the interdiffusion layers, and results show that types of layer have optical basicities significantly greater than that of the glass substrate, through either the high PbO or high Na₂O content.