Sub-Tg mechanical relaxation of a La55Al25Ni20 amorphous alloy

Dynamic mechanical properties of an amorphous La₅₅Al₂₅Ni₂₀ alloy were measured by a forced oscillation method in the temperature range from room temperature to 453 K, just below the glass transition temperature (T_g = 481 K). The internal friction at a constant frequency 62.8 rad/s of this alloy showed a peak at about 400 K and the peak position shifts with frequency. Structural relaxation reduces the magnitude of the relaxation peak but has little affect on the peak position. Using the time-temperature superposition process, master curves for storage E′ (ln ω) and loss E″ (ln ω) moduli are constructed. Activation energy of the relaxation obtained from shift factors is low, 100 kJ/mol, which is close to that for diffusion of the Al in Al and Ni in Al. The relaxation spectra are very broad with a half width of 2 3 decades.     

Electronic conduction in vitreous semiconductors in the pseudo-binary system (As2S3)1-x(PbS)x

AC conductivity and dielectric relaxation measurements of the bulk amorphous compositions in the pseudo-binary system (As₂S₃)_1-x(PbS)_x (x = 0, 0.1, 0.4 and 0.5) in the frequency range 500 Hz-10 kHz and in the temperature span 180–450 K are reported. The temperature dependence of the ac conductivity, σ_ac(ω), has a broad structure at all frequencies in compositions with x = 0.1, 0.4 and 0.5 whose peak position is not thermally activated. A similar structure was also observed in the data on the dielectric constant, ε₁, which peaked at a frequency of 1 kHz in the composition with x = 0.5. Analysis of the results using the correlated barrier hopping model revealed that the electronic conduction takes place by single polaron and bipolaron hopping processes at high and low temperatures, respectively, in compositions containing Pb. The microstructure and phase-separation in the glasses containing Pb influence the electrical transport and dielectric dispersion. This study has revealed the possible presence of a phase transformation at around 300 K at a frequency of 1 kHz in the dielectric dispersion behaviour of composition with x = 0.5.     

Migration of Cu ions in Cu2O---Al2O3---SiO2 glasses on heating in air

The behavior of copper ions in the Cu₂O·Al₂O₃·4SiO₂ (in moles) glass on heating in air at temperatures up to 500°C was studied. When the glass, in which about 90% of Cu was present as Cu⁺ ions, was heated in air above 300°C, a CuO layer was formed on the surface. The amount of CuO was increased with heating temperature and time, corresponding to the decrease in weight of the glass. Furthermore, the fraction of Cu²⁺ ions in the glass increased. These observations suggest that oxygens do not diffuse into the glass, but Cu⁺ ions migrate to the surface from the interior to balance the surplus positive charge produced by the oxidation of Cu⁺ to Cu²⁺ ions inside the glass. The following reaction scheme for the formation of the CuO layer was proposed; 2Cu⁺(interior) + ₂¹O₂(surface) → Cu²⁺(interior) + CuO(surface).     

Time-resolved studies of Ti34−xCu47Zr11Ni8Six metallic glass devitrification using high temperature X-ray powder diffraction

Time-resolved devitrification studies of Ti_34−xCu₄₇Zr₁₁Ni₈Si_x metallic glasses were performed using a recently developed high temperature furnace in a Debye–Scherrer geometry. Samples included powders produced by high pressure gas atomization and surface coatings deposited by air plasma spraying. Synchrotron radiation at the Advanced Photon Source at Argonne National Laboratory was used to follow the devitrification of samples during heating at 40 K min⁻¹ between 623 and 1073 K. The crystallization behavior observed with structural diffraction data compare well with results from thermal analysis using differential scanning calorimetery. At 1073 K, these amorphous alloys evolve to a four phase microstructure which includes phases that appear to be closely related to Cu₅₁Zr₁₄, CuTi and Cu₂TiZr.     

Study of electrical properties of MoO3–Fe2O3–P2O5 and SrO–Fe2O3–P2O5 glasses by impedance spectroscopy. II

The electrical and dielectric properties for three series of MoO₃–Fe₂O₃–P₂O₅ and one series of SrO–Fe₂O₃–P₂O₅ glasses were measured by impedance spectroscopy in the frequency range from 0.01 Hz to 3 MHz and over the temperature range from 303 to 473 K. It was shown in Part I that the MoO₃ is incorporated into phosphate network and the structure/properties are strongly influenced by the overall O/P ratio. The Fe₂O₃ content and Fe(II)/Fe_tot ratio in these glasses have significant effects on the electrical conductivity and dielectric permittivity. With decreasing Fe₂O₃ content in MoO₃–Fe₂O₃–P₂O₅ glasses with O/P at 3.5 the dc conductivity, σ_dc(ω) decreases for two orders of magnitude, which indicates that the conductivity for these glasses depends on Fe₂O₃ and is independent of the MoO₃ content. Also, the dielectric properties such as ^′(ω), ^″(ω) and σ_ac(ω) and their variation with frequency and temperature indicates a decrease in relaxation intensity with increase in the concentration of MoO₃. On the other hand, the dc conductivity for MoO₃–Fe₂O₃–P₂O₅ glasses with O/P > 3.5 increases with the substitution of MoO₃ which has been explained by an increase in the number of non-bridging oxygens and formation of Fe–O–P bonds that are responsible for formation of small polarons. The increase in the dielectric permittivity, ^′(ω) with increasing MoO₃ content is attributed to the increase in the deformation of glass network with increasing bonding defects. For SrO–Fe₂O₃–P₂O₅ glasses the conductivity and dielectric permittivity remained constant with increasing SrO.     

Internal friction and structural relaxation of amorphous Fe---Mn---P alloys

Measurements of internal friction and dynamic modulus have been carried out on amorphous Fe_83−xMn_xP₁₇(x=9,12, or 15) alloys in the temperature range 300–800 K, as a function of applied frequency, by a forced oscillation method. The characteristic transition temperatures and activation energies for crystallization were measured by differential scanning calorimetry (DSC). The viscous flow of the sample was measured using a thermomechanical analyzer (TMA) under continuous heating conditions. Internal friction increases rapidly with temperature starting from 450 K for 0.1 Hz, 474 K for 0.5 Hz, 486 K for 1.0 Hz, 511 K for 5 Hz, and 525 K for 10 Hz for the Fe₇₄Mn₉P₁₇ specimen. It was found that the internal friction peak temperature was very closely the same as the steady state viscous flow temperature from the TMA curves for Fe₇₄Mn₉P₁₇ and Fe₆₈Mn₁₅P₁₇ but not for Fe₇₁Mn₁₂P₁₇. It is assumed that the internal friction peak does not correspond to the glass transition temperature or crystallization temperature for these alloy systems. Two maxima in the free-volume fraction and two minima in the viscosity were also found for the samples which exhibit a ‘mid-contraction’ in their TMA displacement curves. The internal friction peak occurred at the steady state viscous flow temperature. This occurrence means that the origin of the internal friction peak is related to the viscous flow behavior and free-volume fluctuation for this alloy system.     

Homogeneous line width in a zinc borate glass activated by Eu

In this work we report on the temperature depedence of the homogeneous line width (Γ_h) in 4ZnO · 3B₂O₃:Eu³⁺ glass in the region between 30 K and room temperature. The time resolved resonant fluorescence line narrowing technique was applied to the ⁷F₀ ↔ ⁵D₀ transition of Eu³⁺. We obtain that Γ_h follows the commonly found behaviour T² in the whole range of temperature (30–300 K). The Γ_h is comparable to that measured in borate glasses with a small amount of network modifier. This result, together with a linear increase of Γ_h with the excitation energy within the inhomogeneous profile, is indicative of a specific local environment around the Eu³⁺ ion in the zinc borate glass.     

An EXAFS study of Ag3AsS3 glass

The local structures of Ag₃AsS₃ glass at 80 and 300 K have been investigated by extended X-ray absorption fine structure analysis. By comparing the glass structure with that of Ag₃AsS₃ crystal (proustite), the possibility of ionic conduction by this glass is discussed. The local structure around an As atom in the glass is similar to that in the crystal. This fact suggest that, even in the glass structure, the As atoms from AsS₃ trigonal pyramids of shape similar to that in the crystal. The Ag---S distance (2.449 Å at 300 K) and the large root mean square displacement, σ, for the Ag---S atomic pairs in the glass, groups with a by the parameter fitting method, show that the Ag atoms are quite randomly distributed around the AsS₃ groups with a similar Ag---S distance to that in the crystal. Further, it is possible that the large thermal contribution to σ_Ag---S² for the glass may indicate the involvement of the Ag atoms in ionic conduction.     

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.     

Ag precipitation and optical behavior in Na2O---B2O3 glasses

Ag particles of different sizes in the nanometer range were produced in Na₂O---B₂O₃ glasses containing Ag₂O by the melt-quenching and heat-treatment method. The quenching rate was 10³ K s⁻¹ and the heat treatment was at 738 K for 2–300 h. The precipitation was dependent on diffusion limited growth. The optical absorption of Ag particles in the glasses was measured and correlated to the distribution of particle radii. The peak energy of the surface plasmon resonance was blue shifted and the width decreased with increasing average particle radius. These results are compared with previous data on similar systems.     

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.     

B NMR investigations in xV2O5–B2O3 and xV2O5–B2O3–PbO glasses

11B (I=3/2) MAS NMR in the binary glass system xV₂O₅–B₂O₃ (x=0.053, 0.43) and the ternary glass system xV₂O₅–B₂O₃–PbO (0.1x1.5) has been investigated at room temperature. In the xV₂O₅–B₂O₃ glasses, one NMR line due to BO₃ unit was observed. Meanwhile in the xV₂O₅–B₂O₃–PbO, two NMR lines which arise from BO₃ and BO₄ units were detected, where the appearance of BO₄ units is produced by the presence of PbO. From the computer-simulation of the ¹¹B NMR central transition line (m=−1/2↔1/2), the quadrupole parameters (e²qQ/h and η) for BO₃ units in xV₂O₅–B₂O₃, and those for BO₃ and BO₄ units in xV₂O₅–B₂O₃–PbO were obtained as a function of x. As the V₂O₅ content increases in xV₂O₅–B₂O₃–PbO, the e²qQ/h and η values of the BO₃⁻ associated resonance are found to slightly decrease and increase, respectively. Meanwhile, the e²qQ/h and η values of BO₄⁻ associated resonance in xV₂O₅–B₂O₃–PbO are found to slightly increase and decrease, respectively. By comparing the intensities of the total transitions (m=−3/2↔−1/2,m=−1/2↔1/2, and 1/2↔3/2) for the ¹¹B NMR line of BO₃ and BO₄ units contained in xV₂O₅–B₂O₃–PbO with those of respective standard samples of 0.053V₂O₅–B₂O₃ and NaBH₄, the quantitative fractions of BO₃ and BO₄ in xV₂O₅–B₂O₃–PbO were obtained as a function of x.     

Crystallization, neutron irradiation, and annealing studies in glassy Ti50Be40Zr10

We have studied the crystallization and the effects of neutron irradiation and annealing on glassy Ti₅₀Be₄₀Zr₁₀ (Metglas 2204) using resistivity measurements. The resistivity was measured from 2–1000 K for as-received Metglas 2204. Jumps in the resistivity were observed at the various stages during the crystallization process in agreement with previously reported results. Further, the negative temperature dependence of resistivity is affected by neutron irradiation and annealing. In both cases, interpretation of the results in terms of the Ziman theory of liquid metals indicates that the structure factor has sharpened. In the neutron irradiation case the structural relaxation is most likely the result of radiation enhanced diffusion due to the formation of vacancies.     

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.     

Raman spectroscopic study on the structure of ZnCl2---ZnX2 and ZnCl2---KX (X = Br, I) glasses

Raman spectra have been measured for ZnCl₂---ZnX₂ and ZnCl₂---KX (X = Br, I) glasses to investigate the structure of the glasses with varying composition. The assignment of each band was made, and the change of the spectra with composition was explained in terms of the bridging and non-bridging states of halide ions and the change of the tetrahedral units, ZnX_nCl_4−n²⁻ (n = 0–4), formed in the glasses. As the content of ZnX₂ in ZnCl₂---ZnX₂ glasses increases (20 → 80 mol%), the peak frequency of the Zn---Cl stretching mode increases (238 → 248 cm⁻¹ in X = I glasses, 238 → 259 cm⁻¹ in X = Br glasses) while the Zn---I and Zn---Br stretching frequencies decrease (173 → 120 cm⁻¹ for Zn---I, 196 → 157 cm⁻¹ for Zn---Br). The decrease of the Zn---I and Zn---Br band frequencies was attributed to the increase of the number n of the ZnX_nCl_4−n²⁻ tetrahedra. The increase of the Zn---Cl frequency suggests the existence of the bonding state of Cl⁻ ions which is intermediate between the bridging and the non-bridging states. In ZnCl₂---KX glasses, the Zn---Cl_non-bridging band at about 300 cm⁻¹ was observed in addition to the bands observed in ZnCl₂---ZnX₂ glasses. The addition of KX produces non-bridging anions while the tetrahedral units, ZnX_nCl_4−n²⁻ are also formed.     

Physical properties of amorphous Ge20Sb25−xBixSe55 thin films

The influence of substitution of Sb atoms by Bi atoms on the electrical and optical properties of thin films of the Ge₂₀Sb_25−xBi_xSe₅₅ [0x15] system are reported. Results of dc conductivity and thermoelectric power measurements between 150 and 450 K show that the Ge---Sb---Se system is chemically modified by addition of large concentrations of Bi atoms between X=5 and X=10 at.%). A transition from p-type for Sb-doped to n-type for Bi-doped films and a decrease of resistivity is observed. The absorption edge shifts to shorter wavelength, thereby decreasing the optical band gap of the system. Compositional dependences of electrical conductivity, thermoelectric power, and the appearance of n-type conduction are discussed from the stand point of chemical bonds formed in the films and related to the defect states produced due to incorporation of Bi atoms in high concentrations. The coexistence of band and hopping conduction is proposed. The ac conductivity in 0.1–10.0 kHz frequency and 150–450 K temperature range was found to obey a power law σ(ω, T) = Aω^s. The results were interpreted in terms of Elliott's theory, which assumes correlated barrier hopping (CBH) between the charged defect centres. It was found that computed results from the CBH model and experimental one are qualitative agreement for the present materials.     

Bromine-associated defect centers in irradiated ZrF4-based glasses

ZrF₄---BaF₃---LaF₃---AlF₃---NaF (ZBLAN) glasses batched with small additions of NaBr were examined by electron spin resonance (ESR) following their exposure to 100-keV X-rays at 77 K or ⁶⁰Co γ-rays at room temperature. Two sets of radiation-induced ESR spectral features observed for certain of the doped glasses, but not for the undoped control samples, are identified, with the assistance of computer line shape simulation methods, as arising from B₂⁻ and FBr⁻ molecular ions. It is suggested that ESR detection of these species may serve as a diagnostic for bromide impurities in fluoride glasses. The method is used to investigate the retention of bromides by ZBLAN glasses melted under various conditions.     

Growth of Tb3Ga5O12 fiber and bulk crystals using micro-pulling-down apparatus

A micro-pulling-down process, using Ir crucibles and RF heating, has been used to grow single-crystal fiber and bulk crystals of Tb₃Ga₅O₁₂ garnet (TGG). Single crystals ranging up to 450 mm in length have been produced. The crystals were 1–4 mm in diameter and were seeded-grown in the direction close to 1 1 1. The maximal crystal diameter achieved was 10 mm. Dependence of behavior of the solid–liquid interface on the growth parameters (temperature and pulling-rate) is discussed in detail.     

Raman spectra of Ag- and Cu-photo-doped As40S60−xSex films

Raman spectra of the chalcogenide vitreous layers (As₄₀S₆₀, As₄₀S₄₀Se₂₀, As₄₀S₂₀Se₄₀, As₄₀Se₆₀) non-doped and photo-doped by Ag, Cu were measured. The spectra were analyzed in terms of a molecular model. It was ascertained that, for the spectra of photo-doped As₄₀S_60−xSe_x layers, the shift of the main bands to the high frequency side and the appearance of the additional scattering bands in the low frequency spectral range are characteristic features. Variations in the Raman spectra with photodoping by Ag or Cu are consistent with the supposition concerning normal covalent and coordinative bond formation between metal additives and chalcogen atoms, which results in the different activation energy values for the silver photo-stimulated diffusion into chalcogenide layers.     

Structure and properties of the pure and Pr-doped Ge25Ga5Se70 and Ge30Ga5Se65 glasses

The Ge₂₅Ga₅Se₇₀ and Ge₃₀Ga₅Se₆₅ pure and Pr³⁺-doped glasses were prepared by direct synthesis from elements and PrCl₃. It was found that up to 1 mol% PrCl₃ can be introduced in the Ge₂₅Ga₅Se₇₀ and Ge₃₀Ga₅Se₆₅ glasses. Both types of glasses with overstoichiometric and substoichiometric content of Se were homogeneous and of black color. The optical energy gap is E^opt_g=2.10 eV, and the glass transition temperature is T_g=543 K for Ge₂₅Ga₅Se₇₀ and T_g=633 K for Ge₃₀Ga₅Se₆₅. The long-wavelength absorption edge is near 14 μm and it corresponds to multiphonon processes. Doping by Pr³⁺ ions creates absorption bands in transmission spectra, which can be assigned to the electron transitions from the ground ³H₄ level to the higher energy levels of Pr³⁺ ions ³H₅, ³H₆, ³F₂, ³F₃ and ³F₄, respectively. By excitation with YAG:Nd laser line (1064 nm), two intense luminescence bands (1343 and 1601 nm) were excited. The first band can be ascribed to electron transitions between ¹G₄ and ³H₅ energy levels of Pr³⁺ ions. Full width at half of maximum (FWHM) of the intensity of luminescence was found to be 70 nm for (Ge₂₅Ga₅Se₇₀)_1 − x(PrCl₃)_x and (Ge₃₀Ga₅Se₆₅)_1 − x(PrCl₃)_x glasses. The FWHM in selenide glasses is lower than in halide and sulphide glasses. The second luminescence band (1601 nm) can be probably ascribed to the transitions between ³F₃ and ³H₄ energy levels of Pr³⁺ ions. The absorption and luminescence spectra of Pr³⁺ ions in studied glasses are slightly influenced by stoichiometry of glassy matrix. The Raman spectra of studied glasses were deconvoluted and assignment of Raman bands to individual vibration modes of basic structural units was suggested. The structure of studied glasses is mainly formed by corner-sharing and edge-sharing GeSe₄ tetrahedra. The vibration modes of Ga-containing structural units were not found, they are apparently overlapping with Ge-containing structural units due to small difference between atomic weights of Ge and Ga. In the glasses with substoichiometry of Se, the Ge–Ge bonds of Ge₂Se₆ structural units were found. In Se-rich glasses the Se–Se vibration modes were found. In all studied glasses also ‘wrong' bonds between like atoms were found in small amounts. Maximum phonon energy of studied glasses is 320 cm⁻¹.