Internal friction and shear modulus of certain metallic glasses

We have measured the temperature dependence of the internal friction and shear modulus of metallic glass alloys Fe₄₀Ni₄₀P₁₄B₆, Fe₂₉Ni₄₉P₁₄B₆Si₂, Fe₈₀B₂₀ and Fe₇₈Mo₂B₂₀ in the glassy and crystalline phases using a torsional pendulum technique. The internal friction in the glassy phase remains approximately constant from room temperature to a temperature which depends on the annealing treatment, and the rises exponentially with temperature. The internal friction measurements were made at two different frequencies (0.2 Hz and 1.0 Hz) and the activation energies for the relaxation processes estimated by the frequency shift method. The shear modulus increases by about 30% when the amorphous alloys are crystallized. The amorphous alloys Fe₈₀B₂₀ and Fe₇₈Mo₂B₂₀ exhibit Invar type behaviour which disappears upon crystallization.     

Compositional trends in glass transition temperatures in inorganic network glasses

We present a simple mathematical model of glass transition based on the analysis of molecular agglomeration in overcooled liquids. With simple assumptions concerning local configurations and their and bonding energies, and with elementary combinatorics we are able to derive the dependence of the glass transition temperature on chemical composition in non-organic covalent glasses.     

Compositional dependence of the valency state of Cr ions in oxide glasses

Absorption spectra of Cr ions in multi-component oxide glasses melted in Ar were measured. The integrated extinction coefficient is used as a parameter to analyze the redox reaction of Cr³⁺ and Cr⁶⁺ in glass samples. The relative content of Cr⁶⁺ increased and that of Cr³⁺ decreased with increasing basicity in silicate and borate glasses; this result is consistent with previous studies. On the contrary, only Cr³⁺ exist in phosphate glasses. Cr⁴⁺ ions were found only in aluminate, gallate and alumino-silicate glasses with modifier contents ≥ 60 mol%. The relationship between point defects and Cr⁴⁺ formation is examined on the basis of electron spin resonance measurements. We concluded that the superoxide ion radical (O₂⁻) and the peroxy bonding (-O-O-) oxidize Cr³⁺ to Cr⁴⁺ in aluminate, gallate, and alumino-silicate glasses.     

Synthesis of powellite-rich glasses for high level waste immobilization

Increasing amounts of MoO₃ were added to SiO₂-B₂O₃-Na₂O-CaO-Al₂O₃ glasses in order to trap molybdenum as powellite (nominally CaMoO₄). Different heat treatments were performed to study their influences on powellite crystallization by X-ray diffraction and EPR. The glass compositions studied in this work lead to glass-ceramics rich in CaMoO₄, up to [MoO₃] = 5 mol% no poorly durable Na₂MoO₄ phase was identified by XRD. Trivalent actinides surrogates (Gd³⁺) were observed to incorporate into CaMoO₄ crystals.     

Compositional dependence of ultraviolet fluorescence intensity of Ce in silicate, borate, and phosphate glasses

Fluorescence spectra of Ce³⁺ ions in silicate, borate, and phosphate glasses melted in Ar were measured. The relative fluorescence intensity of Ce³⁺ in the ultraviolet region increased in the order of R = Ba, Ca, Sr, and Mg in the 20Li₂O-20RO-60SiO₂ glass samples and with decreasing BaO content in the BaO-B₂O₃ glass samples, respectively. In contrast, the relative fluorescence intensity of Ce³⁺ did not change with varying the glass composition in phosphate glass samples. The compositional dependence of the relative fluorescence intensity of Ce³⁺ is discussed in terms of redox reaction of Ce³⁺-Ce⁴⁺ in oxide glasses.     

Densification of alkali silicate glasses at high pressure

The densification behavior of a number of alkali silicate glasses has been investigated using a Bridgman anvil high pressure device. The pressure range of the investigation was 10 to 60 kilobars; the temperature range was 100 to 400°C. In all cases, the densification was found to increase with increasing temperature and pressure. In the two systems where compositional variations were explored, Na₂OSiO₂ and K₂OSiO₂, a pronounced maximum in densification in the vicinity of 10 mole % alkali oxide was observed (for a given temperature and pressure). These maxima are taken to reflect a competition between two processes, one of which — the variation of molecular mobility with composition — should lead to increasing densification with increasing alkali concentration. Several possibilities are discussed for the decrease in densification with alkali oxide concentrations greater than about 10% (to values smaller than that of SiO₂ in some cases). The present results are related to those obtained in previous investigations of the densification of oxide and polymeric glasses.     

Compositional dependence of the first sharp diffraction peaks in alkali silicate glasses: A molecular dynamics study

The compositional dependence of the first sharp diffraction peaks (FSDPs) of lithium, sodium and potassium silicate glasses were studied by calculating the neutron static structure factors. The advantage of using molecular dynamics simulations is that the contributions of partial structure factors to the FSDPs can be easily determined and provides the basis for detailed analysis. Examination of the correlations of the FSDP with the short and medium range structure reveal that the position and the shape of FSDP strongly depend on the type and concentration of alkali oxide in alkali silicate glasses. The characteristic repeating distances and the characteristic correlation lengths both decrease with increasing alkali oxide concentration indicating a decrease in the intermediate range order. In the lithium silicate glasses, the characteristic correlation length increases with lithium oxide concentration that is anomalous in that the trend is opposite to the other alkali silicate glasses. This anomaly is explained by the high field strength of lithium ions that increases the intermediate range order of the silicon oxygen network.     

Compositional dependences on the mechanism of upconversion in Nd3+/Tm3+ co-doped chalcohalide glasses

Mechanisms of the compositional dependence of blue emission from Nd³⁺/Tm³⁺ co-doped Ge–Ga–S–CsBr chalcohalide glasses were investigated. The blue upconversion emissions (centered at 475 nm) due to the Tm³⁺: ¹G₄ → ³H₆ transition decreased as the CsBr/Ga ratio in glasses while the other upconversion emissions from the Nd³⁺ ions increased. Changes in the local environment of rare-earth ions incurred by the CsBr addition significantly increased the excited state absorption within Nd³⁺ ions. This resulted in the decrease in the Nd³⁺ → Tm³⁺ energy transfer rates that led to the large decrease in blue upconversion emission.     

Compositional dependence of the thermal,structural, and electrical properties of AsTeI glasses

Thermal, structural, and electrical properties of semiconducting AsTeI (and AsTe) glasses have been examined as a function of concentration. Analytical techniques have been developed for quantitative chemical analysis of all three components. Differential scanning calorimetry data indicate a broad endothermic reaction, T_min ∼ 145 °C, above the glass transition (T_g = 120 ± 8 °C) for iodine compositions of 0 to ∼ 20 at%. Above this reaction temperature the thermal data are composition dependent. For glasses with I ? 35 at %, T_g is much lower (65–70 °C) and the endothermic reaction is much sharper with a minimum at ∼ 133 °C. The wide variation in thermal properties with composition suggests that electrical effects associated with high temperatures (e.g. switching and memory phenomena) may also be composition dependent, as well as being dependent upon kinetics. Structural studies show that phase segregation above T_g is dependent upon kinetics as well as upon temperature. Thermal, structural, and electrical data give evidence that As₂Te₃ exists as a unit in the non-crystalline state. This structural unit, stable at high temperatures, is present in the molten material and is thought to be present as the supercooled liquid is quenched. The short-range order extends to long-range order upon devitrification and the first crystalline phase detected is monoclinic As₂Te₃. Apparently metastable under the conditions of formation, this phase converts to a previously unreported fcc phase upon further heat treatment. Similar crystalline structures are known to be associated with thermally- and electrically-induced memory phenomena in AsTeGe and AsTeI glasses. Density measurements at room temperature show that (1) there are no phase miscibility gaps in the glass substructure or different crystalline phases segregating as the I content is varied, and (2) there is a large change in molar volume with increasing I concentration, whereas the molar weight does not change significantly. Electrical conductivity, σ, data in the region around room temperature, show that the σ₀ values, determined from σ = σ₀e^−E/kt, range from 10² to 10³ (Ω-cm)⁻¹. A possible dependence of σ₀ on I content may be due to changes in molar volume. The more homogeneous glasses appear to show breakpoints in the σ versus 1/T data; the corresponding changes in E are only 0.02–0.06 eV, with E = 0.04 eV being most frequently observed. For As₅₀Te_50−xI_x glasses, σ at a given temperature increases as the iodine concentration is increased to about 5 at % and then decreases with further increase in I content. Correspondingly there is a minimum in the E versus I concentration data at I ∼ 5 at %. Results suggest that dependence of the σ breakpoints on glass homogeneity and the variation of E with I concentration may be due to trapping effects.     

Structural studies of solution-made high alkali content borate glasses

The glass forming range of alkali borates has been extended to R = 5.0 (83 mol% alkali oxide) using a solution method. This method involves the reaction between solutions of boric acid (H₃BO₃) and alkali hydroxide (MOH). Physical properties and NMR studies were performed on the intermediate and final glass products of this method. We have obtained results for the entire alkali borate system including lithium, sodium, potassium, rubidium and cesium. The structure of these invert glasses remains enigmatic.     

Sodium ion transport in high purity borosilicate glasses

²²Na diffusion coefficients and dc electrical conductivity were measured in 0.7 B₂O₃·0.3 SiO₂ (mole ratio) glasses containing small amounts of Na₂O (111 ppm to 2.6 mol%). Correlation factors near unity were obtained from the Nernst-Einstein equation for these glasses. These values are in agreement with a previously proposed free “interstitial” alkali ion diffusion mechanism in low alkali content glasses. It is concluded from the low values of the sodium diffusion coefficients and dc conductivity in these glasses (relative to similar silicate and germanate glasses) that the Na⁺ are bound strongly to the borate-rich glass network and that the number of dissociated Na⁺ at any given time is small.     

Structural studies of phosphate glasses with high ionic conductivity

Lithium phosphate glasses with different chemical composition have been studied using infrared absorption spectroscopy (FTIR) and photoelectron spectroscopy (XPS). FTIR and XPS spectra were analyzed to determine the main structural units present in the glass. Absorption bands were identified and assigned to appropriate bond vibrations. It has been shown that analyzed glasses are built up mainly of short chains and rings consisting of metaphosphate structural units - Q². Some pyro- and orthophosphate units Q¹ and Q⁰, respectively are also present. Photoelectron spectroscopy studies have revealed that titanium exists in two valence states: as Ti³⁺ and Ti⁴⁺. Increasing TiO₂ content results in shortening of P-O bonds but leads to elongation of PO bonds in PO₄ tetrahedra.     

Development of novel ternary tellurite glasses for high temperature fiber optic mid-IR chemical sensing

The properties of novel ternary tellurite glasses, based on the TeO₂–BaO–Bi₂O₃ system, are reported for their applications in on-line chemical sensing and process control by characterizing the fundamental frequencies of molecular vibrations in the 2–5 μm spectral region of mid-IR. The chemical sensing for process control also requires above room temperature operation (>100 °C) for prolonged periods of time. Bulk samples of ternary tellurite glasses with a number of different compositions were prepared using heavy molecular weight oxides of TeO₂, BaO, and Bi₂O₃. Infrared and Raman spectroscopic analysis was carried out together with differential thermal analysis to study the relationship between glass structure and thermal and viscosity properties. The temperature dependence of the viscosities of the glasses is also reported. The compositional dependence of Raman frequency shifts and the corresponding change in the coordination of Te–O structure is discussed. The results from the IR edge, reflection spectroscopic, and wavelength dependence of refractive index are also reported.     

Ionic jump processes and high field conduction in glasses

A theory of multiple-ion jumps is proposed to explain the large apparent jump distances which have been calculated from high field conduction in glasses. An analysis of published data on correlation coefficients suggests that multiple ion jumps up to about four ions at a time may occur in single-alkali glasses. In mixed-alkali glasses such processes are shown to be less probable. Measurements of high field conductivity were made on both single- and mixed-alkali glasses, using blown membranes between N/10 acid solutions. The onset of departures from Ohm's law occurred at fields of about 10⁷ V m^?1 from which a jump distance of about 25–30 Å is calculated. This is too large for the proposed multiple-ion jump processes suggested, and, furthermore, the high field currents followed the Poole-Frenkel (PF) law. An alternative theory is given in which the PF law is derived for ionic migration: shallow coulombic potential basins are assumed to be distributed throughout the volume of the glass, owing to non-bridging oxygens whose charge is not balanced by cations on adjacent sites.     

Polynary silicon arsenic chalcogenide glasses with high softening temperatures

The introduction of Ag in SiAsTe glasses permits the incorporation of Se, otherwise volatile and/or degradable as a constituent in Si-containing chalcogenide glasses. SiAsAgTeSe glasses exhibit much higher softening ranges and glass transition temperatures than encountered in known chalgogenide systems. A glass Si₃₅As₁₅Ag₁₀Te₂₀Se₂₀ had the viscosity log ν = 13 at about 500°C, as compared to 370°C for the base glass Si₃₅As₂₅Te₄₀, the viscosity of log ν = 9.8 at about 560°C, as compared to 442°C for the base glass. Phase separation occurs in the system SiAsAgTeSe and becomes manifest in two glass transitions indicated by changes in the slopes of the expansion curves and breaks in the softening point-composition relations. The existence and behavior SiAsAgTeSe glasses suggests the possible development of higher T_g i.r. transparencies and higher T_g semiconductor glasses than described so far.     

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.     

Properties of some high Al content glasses in various lanthanide-Si-Al-O-N systems

A review of some behaviour diagrams in the Y-Si-Al-O-N system indicate that the liquid region, and hence the glass forming region, could be more extensive than previously documented. Apart from the glass-forming region of Drew et al. [Special Ceramics 7, Brit. Ceram. Proc., vol. 31, The British Ceramic Society, Stoke-on-Trent, UK, 1981, p. 119] at 1700 °C, the solid-liquid reactions in the β-SiAlON-Y₃Al₅O₁₂ seen as liquid isotherms at 1550, 1650 and 1750 °C are indicated by Tien [Silicon Nitride Ceramics Scientific and Technological Advances, Materials Research Society Symposium Proceedings, vol. 287, MRS Pittsburgh, 1993, p. 51]. Other researchers [J. Eur. Ceram. Soc. 17 (1997) 789] have studied the nitrogen-rich liquid phase regions in the Ln-Si-Al-O-N systems (40 e/o N). In the current work, selected compositions with high Al/Si ratio in the aluminium-rich part of these systems (52-62 e/o) were fired at 1700 °C. Properties have been investigated and compared with ‘standard’ glass compositions (i.e. 28M:56Si:16Al:83O:17N e/o) [J. Eur. Ceram. Soc. 17 (1997) 1933] where M=La, Nd, Sm, Dy, Er, Yb, Y.     

High-temperature growth of very high germanium content SiGe virtual substrates

We have first of all studied (in reduced pressure–chemical vapour deposition) the high-temperature growth kinetics of SiGe in the 0–100% Ge concentration range. We have then grown very high Ge content (55–100%) SiGe virtual substrates at 850 °C. We have focused on the impact of the final Ge concentration on the SiGe virtual substrates’ structural properties. Polished Si_0.5Ge_0.5 virtual substrates were used as templates for the growth of the high Ge concentration part of such stacks, in order to minimize the severe surface roughening occurring when ramping up the Ge concentration. The macroscopic degree of strain relaxation increases from 99% up to values close to 104% as the Ge concentration of our SiGe virtual substrates increases from 50% up to 100% (discrepancies in-between the thermal expansion coefficients of Si and SiGe). The surface root mean square roughness increases when the Ge concentration increases, reaching values close to 20 nm for 100% of Ge. Finally, the field (the pile-up) threading dislocations density (TDD) decreases as the Ge concentration increases, from 4×10⁵ cm⁻² (1–2×10⁵ cm⁻²) for [Ge]=50% down to slightly more than 1×10⁵ cm⁻² (a few 10⁴ cm⁻²) for [Ge]=88%. For [Ge]=100%, the field TDD is of the order of 3×10⁶ cm⁻², however.     

On the anomalies in density,Young's modulus and glass temperature of PdSi glasses

The densities, Young's moduli and glass transition temperatures have been measured for binary PdSi glassy alloys. These glassy alloys exhibit a negative deviation from Vegard's law an enhancement in Young's modulus and a tendency to lower the glass transition temperature in the region of the eutectic composition. The observed nonlinearity in these physical properties is shown to be better agreement with an alloy mixing effect rather than the structural ordering model.