The kinetics of formation of A AuGeSi metallic glass

The glass-forming ability of a Au_0.778Ge_0.138Si_0.084 alloy is analyzed theoretically by computing a time-temperature-transformation curve which describes the time required to produce a barely detectable fraction of crystallization, at various temperatures. The calculation is based on an interpolated viscosity-temperature curve, this alloy being exceptional among metallic glass formers in that experimental viscous-flow data are available at both high and low temperatures. Allowing for uncertainties, the critical cooling rate for glass formation lies within the range 10⁶?10⁸ K/sec which is in satisfactory agreement with experimental estimates of cooling rates in splat quenching. This and previous comparisons for Ni and PdSi alloys suggest that the approach may have useful and general applicability to metallic glasses.     

Mechanical damping of silver-containing SiAsChalcogenide glasses

Mechanical damping measurements were used to study the structural conditions responsible for the increase in thermal stability that has been observed when Ag and Se are substituted simultaneously in Si₃₅As_25?xAg_xTe_40?ySe_y glasses. Glasses containing Ag exhibited a mechanical damping peak whose magnitude was approximately proportional to the Ag content and which was absent in the more completely cross-linked Si₃₅As₂₅Te₄₀ base glass. This peak shifted to lower temperatures and split into two overlapping peaks with increasing Se content. The splitting of the peak has been tentatively attributed to phase separation which has been postulated to occur at higher Se contents.     

Composition dependence of the glass transition temperatures of PdNiP and PtNiP glasses

Thermal properties of glassy PdNiP and PtNiP alloys have been measured as a function of the concentration of transition metals. The glass transiion temperature, T_g, of these alloys glasses exhibits a negative linear deviation with transition metal content - which is in contrast to the increasing T_g of binary glassy alloys with increasing metalloids.It is suggested that the suppression of the glass transition temperature of these glassy alloys may be attributed to the excess configurational entropy of disorder associated with a mixture of hard spheres differing in radius. In contrast, the increasing T_g of binary glassy alloys with the metalloid content may be associated with the short-range order resulting from strong interactions between metal and metalloid atoms.     

Memory effect in CuAsSe glasses containing small amounts of Au

The Cu, As and Se contents of Au-containing CuAsSe glasses significantly affected both the resistivity in the memory state and the time required to reach the memory state, whereas the Au content affects only the latter. The main crystalline species formed in these glasses was a CuAsSe compound, and its formation was enhanced by the addition of Au. The role of Au in the memory effect was discussed on the basis of crystallization behavior of glasses.     

The leaching behavior of PbOSiO2 glasses

The leached layer of PbOSiO₂ glasses formed by diluted nitric acid solution has been investigated by ellipsometry and Auger electron spectroscopy (AES). The leaching behavior of PbOSiO₂ glasses in 10^?4 N aqueous solution of NHO₃ at 30°C was measured in real time using a Nikon auto-ellipsometer.The results were applied by curve fitting to the two-layer model from the concentration profile obtained by AES, and the refractive index profile against the film thickness was determined.The leached layer is inhomogeneous and consists of a low refractive index region and a transition region. The gradient of the refractive index in the former region is extremely small and the refractive index becomes nearly constant between 1.42 and 1.44. The shape of latter region becomes stable with its thickness at 100–310 Å, and moves in the direction of depth without changing the shape as the leaching proceeds.     

The study of transformation kinetics of the amorphous PdSi alloys

The kinetics of transformation behavior of roller-quenched amorphous Pd₈₃Si₁₇ and Pd₈₀Si₂₀ alloys after linear and isothermal heating is reported. The transformation was examined with electron microscopy, electron diffraction and electrical resistivity measurement. The crystallization of amorphous alloys with 17 at% Si begins with metastable ordered fcc solid solution. The ordered fcc solution is transformed to a ordered metastable phase with, probably, orthorhombic structure. The crystallization of amorphous alloys with 20 at% Si begins by formation of spherulites with lamellar structure. Using electron diffraction we found that spherulites consist of two phases - orthorhombic Pd₃Si silicide and Pd-rich silicide. From resistivity measurements, activation energies of 28.5 kcal/mol for Pd₈₃Si₁₇ and 80 kcal/mol for Pd₈₀Si₂₀, respectively, were calculated.     

Thermoelectric power of AsSeTe glasses

The result of the measurement of the thermoelectric power of glasses in the As₂Se₃As₂Te₃ system are reported. The results indicate that towards the As₂Te₃ end of the composition, there is an anomalous increase in thermoelectric power, the origin of which is not clear. Polaron hopping seems to contribute to conductivity in tellurium rich glasses. Structural restrictions on polaron hopping, such as the availability of AsTeAsTe chains seems to be important in discussing transport behaviour.     

Change in corrosion behavior of amorphous FePC alloys by alloying with various metallic elements

Comprehensive work to examine the effect of metallic alloying elements M on the corrosion behavior of amorphous FeM13 P7 C alloys was performed. All alloying elements except manganese are effective in increasing the corrosion resistance of amorphous alloys in various acidic and neutral solutions, regardless of anionic species, pH and oxidizability. The addition of elements more active than iron to amorphous FePC alloy decrease the corrosion rate in an active region during immersion tests, depending upon the passivation capabilities of the alloying elements themselves. When elements nobler than iron are added, the nobler is the alloying element, the higher is the corrosion resistance of amorphous FeM13 P7 C alloys.     

ESR study of Mn2+ in GeTe and GeTeSi glasses

The electron spin resonance spectra of Mn²⁺ ions have been studied in Ge_xTe_100?x with x = 15, 17.5 and 20, and Ge_20?xTe₈₀Si_x with 0 ?x? 20. All samples are found to exhibit six hyperfine lines centered at g = 4.3 with hyperfine interaction constant A = 56 × 10^?4cm^?1. The g = 4.3 line is interpreted as being caused by Mn²⁺ ions incorporated in the amorphous network and surrounded by four Te atoms in an arrangement of orthorhombic symmetry. Some of the samples of GeTe show a g = 2.0 line. This line also appears after heat treatment in air at temperatures above the glass transition temperature. It is concluded that the g = 2.0 line is caused by Mn²⁺ ions in phase separated microcrystalline or concentrated regions of MnO in the glass.     

Photoconduction of glasses in the TeSeSb system

The photoconductivity of bulk glasses of the TeSeSb system is measured as a function of light intensity and photon energy. The relative sensitivity (ΔI/I_d) has linear and square-root dependences on light intensity in low and high illumination intensities, respectively, and is nearly proportional to the square-root of the resistivity at room temperature. The spectral response of photoconductivity, which is calculated by taking into account the effect of surface recombination of carriers, agrees qualitatively with the experimental results. The experimentally determined broad spectral response suggests the presence of band tails below the conduction band and above the valence band. The large residual dark conductivity in the decay response is associated with the presence of many deep trapping centers.     

Sensitivity of the photo-darkening effect in CuAsSe glasses

When CuAsSe glasses are irradiated, they exhibit higher concentrations of darkening than AsSe glasses. Since darkening depends on the composition, the darkening centers in CuAsSe glasses to be of the same kind as those in AsSe glasses, i.e. arsenic clusters. Concerning the kinetics of erasing, it was found that the activation energy and the rate constant of erasing in CuAsSe are almost equal to those in AsSe glasses, but for the kinetics of darkening, it was found that the activation energy of darkening is equal to that of AsSe but α₀, which is proportional to the number of latent darkening centers, and the darkening rate constant k₁ are about twice as high as the corresponding constants of AsSe glasses. This may be the reason for the greater darkening in CuAsSe glasses. The high value of α₀ was attributed to the generation of more AsAs bonds on the addition of Cu to the AsSe glass network. The high value of k₁ was attributed to the increase in efficiency of photo-decomposition because of the many impurity levels in the band gap and also because of the narrow optical energy gap in the CuAsSe glasses.     

Quenched-in excess volume and structural relaxation in Ni- and FeNi based metallic glasses

The amount of quenched-in excess volume (ΔV_R) in various Ni- and FeNi based metallic glasses, which is defined by the volume change due to the structural relaxation, was estimated from measurements of length changes caused by isochronal annealing. It was found that the values of ΔV_R depend greatly on the kind of transition metals (Fe, Ni) and metalloids (Si, B, P) and their ratios (Fe/Ni, Si/B). In non-magnetic Ni-based metallic glasses, almost a linear relationship was observed between the changes in volume and electrical resistivity during the low temperature annealing below around 275°C. Furthermore, a large ΔV_R was observed in the metallic glasses which have a large thermal expansion coefficient such as Ni₇₅Si_12.5B_12.5 or which exhibit a well-defined glass transition such as Fe₂₇Ni₅₃P₁₄B₆, as a general trend. These results indicate that the amount of quenched-in excess volume is very sensitive to the local atomic arrangement and is attributed mainly to the distribution in bond lengths, angles and coordination numbers in the short range structure and the difference in packing of basic structural units between as-quenched and relaxed glassy states.     

Mechanical properties of NiFe based alloy glasses

The ductility and tensile strength of NiFe based alloy glasses prepared by the ‘roller quenching’ technique were investigated. These alloy glasses are intrinsically ductile and possess a high tensile strength. However, the mechanical properties of glasses which are predominantly Fe are very susceptible to the quenching conditions, and such glasses tend to be brittle. It is suggested that the hot rolling of the alloy during quenching is responsible for the brittle behavior. Tensile strengths as high as 230 000 psi were obtained for the NiFe based alloy glasses.     

Raman scattering study of BaF2ZrF4FeF2 glasses

Several BaF₂ZrF₄ glasses containing 5 mol% FeF₂ have been studied to elucidate the fraction of nonbridging fluorine atoms (−F⁻) in a ZrF₆ octahedron constituting a zigzag chain. A continuous increase in the fraction of nonbridging fluorine atom in a ZrF₆ octahedron is deduced from the increase in the integrated peak intensity of the symmetric stretching-vibrational mode (ν^s) for the Zr-nonbridging fluorine atom when the BaF₂ (+ FeF₂) content is lower than 38 mol%, i.e., in the composition region where the average coordination number of Zr is regarded as six. This result is well consistent with the previous results obtained from Raman studies of binary BaF₂HfF₄ glasses, and also with those of Mössbauer and Raman studies of ternary BaF₂ZrF₄FeF₂ glasses. A drastic decrease in the symmetric-stretching vibrational mode (ν^s) in 42BaF₂·53ZrF₄·5FeF₂ glass suggests that a friction of ZrF₆ octahedron is reduced when BaF₂ (+FeF₂) content is close to 50 mol%. The zigzag chain is therefore considered to be constituted of ZrF₇ units in such glasses.     

Far infrared transmission and structure of PbGeS semiconducting glasses

Lead sulfide has been found to form stable glasses with GeS₂ in the presence of GeS. Far-infrared transmission spectra of the glassy compositions x = 0.46, 0.23 and 0.115 in the pseudoternary (PbS)_x (GeS₂)_0.70?x (GeS)_0.30 and of the stoichiometric crystalline composition Pb₂GeS₄ have been observed for the first time. The results indicate a two optical mode behaviour of the compounds. The presence of the heavy lead atom in the GeS network seems to appreciably affect the bond bending modes of the GeS₄ molecular unit without significantly disturbing its bond stretching vibrations. The presence of S₃GeGeS₃ molecular units in the amorphous compositions and their absence in Pb₂GeS₄ are indicated.     

Formation of glass in the GeSiS system

The formation of glass in the GeSiS system was investigated. After synthesis of material with the general formula Ge_1?xSi_xS_y, where x was chosen to be 0.05, 0.1, 0.2, 0.3 and y was in the range 1.28–3.6, cylindrical samples were prepared and used for the characterization of glass by means of DTA. It was found that the substitution of germanium with silicon does not lead to any expressive change of the glass transition temperature, crystallization and the onset of melting.     

Thermal expansion and density of glassy PdNiP and PtNiP alloys

Thermal expansion and density of (Pd_1?xNi_x)_0.80P_0.20 and (Pt_1?yNi_y)_0.75P_0.25 alloys in their various states have been measured from room temperature to the glass transition temperature T_g. The thermal expansion of the glassy alloys at room temperature varies linearly with x and y and is 10 to 20% higher than that of corresponding pure metals. The thermal expansion of the undercooled alloy liquids near T_g as well as the molar volume $\text{v}\text{?}$ deduced from the density of glasses in contrast exhibits a negative deviation with composition x and y.This behavior is in line with the previously reported negative deviation of the glass transition temperature of these glassy alloys with metal content and may be explained in terms of excess volume associated with a mixture of hard spheres.     

Crystallization of some semiconducting chalcogenide glasses in the AsSeBi system

Isothermal crystallization in vacuum and in air was studied in glassy As Se_1.5Bi_0.05 at 240 and 260°C. Electrical properties, density, and microhardness were measured. X-ray diffraction of the annealed samples was also examined.Unlike As Se_1.5, As Se_1.5Bi_0.05 easily crystallizes. The first process of devitrification has an induction period (characteristic parameters suffer little changes). As crystallization increases, the density of the alloys also increases and the microhardness decreases. The electrical conductivity increases at 20°C by 6–7 orders of magnitude and the activation energy of electrical conductivity decreases by about 1.7 eV.     

Electrical conductivity of GeTe glasses under hydrostatic pressure

The electrical conductivity of some GeTe bulk glasses has been measured between 10 and 80°C under hydrostatic pressure up to 3000 bar. The electrical conductivity (σ) of as-prepared, amorphous samples can be expressed by an equation: σ = A exp (?B/kT). For Ge₁₇Te₈₃ glass, the pressure dependences of the constants, A and B, are: (d ln A/dp) = ?3.2 × 10^?4 bar^?1 and (dB/dp) = ? 2.1 × 10^?5 eV · bar^?1. The results are analysed in terms of the low-mobility band model of Mott-CFO for amorphous semiconductors.     

DC conductivity of ZnOV2O5 glasses

This work presents for the first time results regarding the DC conductivity of glasses belonging to ZnOV₂O₅ system. It is shown that the conduction can be described by a small polaron hopping model. The high temperature activation energy and conductivities are close to the values determined for V₂O₅P₂O₅ glasses of similar composition. The analysis of the pre-exponential factor shows strong evidence for a non-adiabatic conduction regime.This fact agrees with the conclusion drawn for the majority of vanadate glasses. The strong variation of α suggests the presence of fluctuations in the V⁵⁺ surroundings.