On the number of amorphous phases in n-butanol: Kinetics of free radicals oxidation by oxygen in frozen n-butanol

We report on the discovery of a new solid, presumably amorphous n-butanol at ambient pressure. According to the literature data the melting point T_m of n-butanol is 183 K and the glass transition temperature T_g is 118 K. If kept isothermally at a fixed temperature between 130 and 160 K, the supercooled liquid n-butanol undergoes remarkable phase transformations to a solid phase. The new phase converts to liquid at a temperature of about 170 K. It is presumably amorphous because foreign substances dissolved in liquid n-butanol keep the same state in this new phase of butanol. The kinetics of free radical oxidation by dissolved oxygen in both solid amorphous phases is investigated in detail.     

Hall resistivity of a magnetic amorphous alloy — Effects of thermal cycling and annealing

We have studied the effects of thermal cycling and annealing on the Hall resistivity ?_H and electrical resistivity ? of an amorphous magnetic material, Metglas 2826A. Thermal cycling up to 600 K has no significant effect on ? but changes ?_H, especially at T > 300 K. Annealing at higher temperatures T_a affects ?_H more strongly that it influences ?. For T_a = 650 K the Curie temperature jumps by ～300 K and this, combined with X-ray data, is regarded as being symptomatic of the onset of crystallization. It is demonstrated that, for a fixed T, the variation of the extraordinary Hall coefficient R₁ is simply correlated with that of ? for both the amorphous material and the annealed (crystallized) specimens. Furthermore, for a given T_a, the variations of R₁ and ? as functions of temperature exhibit the same formal relationship. The temperature dependence of ? in the annealed specimens is rendered plausible in terms of recent theories of disordered materials. Room-temperature studies of electron spin resonance and the field dependence of the magnetization are also reported.     

Photoemission (UPS and XPS) study of local structures of amorphous GeTe and GeSe films

In situ photoemission (UPS and XPS) measurements have been performed for amorphous GeTe and GeSe films deposited onto a cooled substrate during thermal annealing and crystallization of the films. It has been found that an amorphous film prepared at room temperature has a 4-2 coordinated local structure while a highly disordered film deposited onto a 77 K substrate is largely 3-3 coordinated and relaxes into the 4-2 coordinated structure upon thermal annealing.     

Transport properties of amorphous germanium prepared by the glow discharge technique

The paper deals with conductivity, thermoelectric power and field effect measurements on amorphous Ge specimens prepared by the decomposition of germane gas in a rf glow discharge. Substrate temperatures T_d of 300, 400 and 500 K were used during deposition. The sign of the thermoelectric power S is negative throughout the temperature range investigated (200–500 K). Above 300 K, the conductivity activation energy in specimens prepared at T_d = 500 K lies between 0.40 and 0.43 eV; it is equal to the gradient of the S versus 1/T curves, suggesting transport in the extended electron states. Below room temperature there is an increasing contribution in all specimens from electron hopping transport in localized states lying about 0.25 eV below ?_C. Both conductivity and thermoelectric power results can be interpreted satisfactorily in terms of these two current paths. Hopping at the Fermi level has not been observed. The preliminary field effect measurements indicate that, as in amorphous Si, ?_f lies near a density of state minimum. The density of states at ?_f is appreciably higher than that in similarly prepared Si specimens.     

Crystallization temperature of amorphous Fe80B20 under pressure

The resistance of rapidly quenched Fe₈₀B₂₀ was recorded versus T at a rate of 7 K/min and various pressures up to 2.5 GPa. The onset of crystallization, T_x, was defined by extrapolation at the sharp change in resistance associated with crystal growth. The resulting slope of T_x is 15 K/GPa. Separate measurements at atmospheric pressure yielded T_x versus rate of temperature increase, R = dT/dt. crystallization times from the literature were recalculated to yield T_x, and the results are compared with our data. Nominally amorphous materials of the same composition show markedly different properties. It is also shown that the variation of T_x with R is mostly due to the change in viscosity.     

Crystallization behaviour of an amorphous Ti50Be40Zr10 alloy

The crystallization behaviour of an amorphous Ti₅₀Be₄₀Zr₁₀ alloy during a continuous heating mode from room temperature to 973 K and isothermal annealing at temperatures above the glass transition temperature is examined by differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS) measurement and large-angle X-ray diffractometry (LAXD). DSC indicated two well-defined exothermic peaks, a slight shoulder at the higher temperature side of the second peak and a small heat evolution at higher temperature. The Kissinger plot for the first and the second peak gives a straight line, from which the apparent activation energy is estimated to be 269 and 413 kJ/mol respectively; the enthalpies for the first and second crystallization process are 1.04 kJ/mol and 4.39 kJ/mol for a heating rate of 20 K/min. The SAXS intensities increase sharply after annealing at about 673 K (corresponding to the first peak in the DSC curves); the scattering is due to the formation of fine-scale crystalline Ti particles by the LAXD. The size of the particles does not change significantly while the number of scattering particles increases, indicating that the reaction is almost nucleation controlled and the growth is very limited. Another crystalline phase would appear in addition to the Ti particles on annealing at temperatures above about 753 K (corresponding to the second peak in the DSC curves), where the SAXS intensities decrease compared with those for only the first-stage of crystallization. The crystalline phase might be a metastable cubic phase with the lattice parameter a₀?0.2994 nm.The sequence in the crystallization of the initial non-crystalline material is amorphous → microcrystalline (MS I) → crystalline (MS II; S III), although the structure of crystalline phase in the final stage (S III) was not identified. It is also likely that cold-rolling does not have a perceptible effect on the crystallization behaviour of the present amorphous alloy.     

Pressure and temperature dependence of the electrical resistivity of bulk Al23 Te77 glass

Electrical resistivity of bulk amorphous Al₂₃T₇₇ samples has been studied as a function of pressure (up to 80 kbar) and temperature (down to 77 K). At atmospheric pressure the temperature dependence of resistivity obeys the relation ? = π₀ exp(δE/RT) with two activation energies. In the temperature range 300 K ? T > 234 K the activation energy is 0.58 eV and for 234 >T ? 185 K the value is δE = 0.30 ev. The activation energy has been measured as a function of pressure. The electrical resistivity decreases exponentially with the increase of pressure and at 70 kbar pressure the electrical behaviour of the sample shows a metallic nature with a positive temperature coefficient. The high pressure phase of the sample is found to be a crystalline hexagonal phase.     

Temperature-induced changes in physical properties and lattice symmetry of nickel crystals

It has been shown that the changes in some physical properties of nickel crystals can be explained on the assumption of the existence of an isotropic magnetic phase within the temperature range 470 < T < 631 K, whose thermodynamic properties are determined by the exchange interaction alone. At T _is ≈ 470 K, this phase should be transformed into an anisotropic magnetic phase because of the cooperative effect of relativistic interactions. This provides a consistent interpretation of the changes in the symmetry and the number of physical characteristics of the crystal in the framework of the Landau theory within the temperature range 273 < T < 650 K.     

Crystallization of amorphous Ni35Zr65 and Fe40Ni40P14B6 under proton irradiation

Two amorphous alloys, Ni₃₅Zr₆₅ and Fe₄₀Ni₄₀P₁₄B₆, were irradiated using 400 keV protons at several temperatures below the crystallization temperature, T_x, to peak doses in the neighborhood of 3.5 to 4.5 dpa. Irradiation at 250°C resulted in the crystallization of both alloys, which were examined by transmission electron microscopy of samples electrolytically polished to various distances from the irradiated surface to study the effect of dose. Samples masked from the proton beam remained amorphous during irradiation. In the Ni₃₅Zr₆₅ alloy crystallization of the equilibrium phases propagated throughout the entire sample, while the in the Fe₄₀Ni₄₀P₁₄B₆ alloy crystallization was observed only in those parts of the samples lying within the proton range. Neither alloy crystallized during irradiation at 100°C. In both these alloys the amorphous phase is therefore evidently stable at irradiation temperatures below approximately 0.6 T_x. An examination of the literature on irradiation damage of binary alloys and intermetallic compounds suggests that there is a tendency for initially amorphous alloys to remain amorphous at irradiation temperatures, T_irr < 0.3 T_L, where T_L (≈T_x) is the “melting” temperature (either a eutectic, peritectic or congruent melting temperature). Also, these same alloys, even when they are initially crystalline, transform to the amorphous state during irradiation at T < 0.3 T_L. Some other crystalline alloys have also been shown to transform to the amorphous state at T_irr < 0.3 T_L even though they have never been prepared in this condition by rapid quenching techniques. The temperature 0.3 T_L appears to be a lower limit, however, since the crystalline to amorphous transformation occurs in many of these alloys at temperatures greater than 0.3 T_L. It is suggested, by analogy with results on void formation in irradiated metals, that this low temperature limit is related to the low mobility of vacancies in these materials, although the mechanism of crystallization, or conversely amorphization, is not fully understood.     

Crystallization processes in amorphous Zr54Cu46 alloy

The crystallization of amorphous Zr₅₄Cu₄₆ alloy was investigated by using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) techniques. The experimental results show that an endothermic peak in DSC traces for amorphous Zr₅₄Cu₄₆ alloy exists at about 1006 K, indicating following eutectoid reaction occurs, namely, Cu₁₀Zr₇+CuZr₂↔CuZr in amorphous Zr₅₄Cu₄₆ alloy during heating. With increasing the heating rate, the glass transition temperature T_g and onset crystallization temperature T_x of amorphous Zr₅₄Cu₄₆ alloy increase in parallel, and the supercooled liquid region ΔT_x (=T_x−T_g) holds almost constant with an average value of 44 K. Both XRD and TEM results prove that Cu₁₀Zr₇ and CuZr₂ are main crystallization products for amorphous Zr₅₄Cu₄₆ alloy under continuous heating conditions. No CuZr phase is identified because of its small precipitation amount. Finally, the crystallization processes of amorphous Zr₅₄Cu₄₆ alloy were summarized.     

Structures of vapour-deposited amorphous films of arsenic chalcogenides

The structures of vapour-deposited amorphous films of composition As_xSe_1?x′, with x between 0 and 1, have been investigated by X-ray diffraction. In all cases the structure of the freshly deposited film differs very considerably from that of the corresponding bulk glass. For the elemental amorphous films the structure is highly disordered and contains voids which for Se cannot be annealed out below the crystallization temperature of 70°C or, for As, below the temperature ($\text{?130°}\text{C}$) where the As film re-evaporated. Annealing of the arsenic selenide films at temperatures below T_g causes the structures to relax towards those of the bulk, with a distribution of activation energies around 25 kJ mol^?1. The composition of the vapour has been examined by mass spectroscopy and it is concluded that even if some molecular identity is retained on condensation there must be considerable cross-linking to give the observed structural behaviour.     

Structural instabilities,incommensurate modulations and <Emphasis Type="Italic">P</Emphasis> and <Emphasis Type="Italic">Q</Emphasis> phases in sodium niobate in the temperature range 300–500 K

The relation between the phase transition in the vicinity of 420 K discovered earlier and the formation of an incommensurate phase in the temperature range 410–460 K is established based on the X-ray, dielectric, and dilatometric studies of sodium niobate (NaNbO₃) single crystals and ceramics. It is also established that this phase is characterized by temperature and temporal instabilities. Anomalies in some physical characteristics in the vicinity of 350 K are revealed. It is also shown that the thermodynamic history of the samples is important for the coexistence of the regions of the ferroelectric Q and antiferroelectric P phases in NaNbO₃.     

Electrical and optical properties of amorphous boron and amorphous concept for ß-rhombohedral boron

Measurements of the conductivity (σ), thermoelectric power (S) and thermal conductivity (κ) of amorphous boron are made over wide temperature ranges (T = 77–850 K for σ, T = 300–850 K for S and T = 80–1100 K for κ). The room temperature spectral dependencies of the reflection (R) and absorption (α) coefficients are determined for the wavelength intervals 2–25 μm and 1.3–25 μm respectively. The I–V characteristics are also studied and shown to be consistent with the Poole-Frenkel law.The value obtained for the thermal energy gap of amorphous boron (1.3 eV) is slightly smaller than that of crystal ß-rhombohedral boron (1.4 eV). The temperature dependence of the electrical conductivity can be satisfactorily described by the Mott law $\text{ln}\text{σ ≈ ?(T}{}_0\text{/T)}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$, where $\text{T}{}_0\text{? 10}{}^8\text{K}$. This gives an estimate, N ≈ 10¹⁸ cm^?3, for the concentration of trapping levels responsible for the hopping conduction. The value $\text{?}{}_0\text{? 9}$ is found from the spectral dependence of R while α has Urbach-like character $\text{? α ≈}\text{exp}\text{(}\text{h}\text{?}\text{ω/Δ)}$, where $\text{Δ ? 0.19}\text{eV}$.A comparison is made between amorphous boron and crystalline ß-rhombohedral boron. Because of the very complex crystal structure and the large dimensions of the unit cell of ß-boron, some of its physical properties could be qualitatively described on the basis of the so-called ‘amorphous concept’.     

Thermodynamics of formation of aluminum-iron-germanium amorphous alloys

Thermodynamic properties of ternary liquid Al-Fe-Ge alloys were studied by electromotive force method at 1050-1250 K and by high-temperature isobasic calorimetry at 1740 ± 5 K. The heat capacity change at ternary alloy formation (Δ_mixC_p) was estimated using the temperature dependence of integral enthalpy of mixing. Thermodynamics of the formation of Al-Fe-Ge amorphous alloys was evaluated by extrapolation of thermodynamic functions of mixing to the temperature of amorphization. The process of glass forming is preferable by both enthalpy and entropy for compositions of (0.1<x_Fe<0.6, x_Ge<0.5). The area with most negative integral Gibbs free energy and enthalpy of amorphous alloy formation corresponds well to the area of amorphization estimated by a glass-forming tendency (GFT) criterion.     

Sound velocity in liquid and glassy selenium

The speed of longitudinal sound waves at 7 and 22 MHz has been measured in liquid, supercooled, and amorphous selenium, including the region around the glass transition temperature, T_g, near 35 °C. In amorphous selenium the speed of shear waves at 7 MHz was also measured. The experiments were performed with high purity Se (99.9999%) hermetically sealed in an evacuated silica ampoule. Four temperature regions with strongly different relaxation times can be distinguished between room temperature and the melting point: (1) a glassy state below T_g, which is stable on the time scale of the experiments, (2) a glassy state above T_g, which is metastable on the time scale of the experiments, (3) a region where homogeneous crystal nucleation occurs, and (4) a supercooled liquid, which is stable on the time scale of the experiments. Each region is marked by a change in the slope of the temperature dependence of the sound velocity. Near the glass transition temperature the velocities of longitudinal and transverse sound exhibit hysteresis with a step-like drop on heating and a more continuous rise on cooling. The step-like anomaly in sound velocity may be a general property of the glass transition.     

The structure of amorphous carbon tetrachloride by neutron diffraction

A vapour-deposited sample of amorphous CCl₄ at 10 K has been studied by neutron diffraction. The measured structure factor confirms that the basic molecular unit is retained in the amorphous phase and a form-factor fit to the high Q-value data gives a CCl bond length of (1.770±0.002) Å. The inter-molecular function, D_M(Q) shows more structure than for the liquid phase and transformation to a real-space distribution function confirms that this is due to a much stronger orientational correlation between adjacent molecules in the amorphous solid. The density is found to be (25±5)% higher than in the liquid and the structural properties can be well described using a reference interaction site model (RISM).     

Neutron diffraction studies of vapour-deposited ammonia-ND3

A vapour-deposited sample of ND₃ at 10 K was studied by neutron diffraction and found to consists of a mixture of crystalline and amorphous material. The Bragg peaks were in good agreement with those for the cubic crystalline form of ND₃ and could be subtracted to give the diffraction pattern for the amorphous solid. The data for the amorphous phase were transformed to give the real-space distribution function d(r) which contained significant oscillations for r-values extending to 15 Å. Comparison of the data with that of liquid ND₃ shows a structural change which is consistent with the formation of a random network of hydrogen-bonds. This behaviour resembles that observed in water and amorphous ice but has several important differences resulting from the dimensionality of the network.     

Structural,dielectric and optical properties of transparent glasses and glass-ceramics of SrBi2B2O7

Optically clear glasses of SrBi₂B₂O₇ (SBBO) were fabricated via the conventional melt-quenching technique. The amorphous nature of the as-quenched samples of this compound was confirmed by X-ray powder diffraction (XRD) studies. Its glassy nature was established by differential scanning calorimetry (DSC). However, the optical microscopy revealed the presence of isolated hexagonal shaped crystallites especially at the edges of the as-quenched glasses. The glass plates that were heat-treated around the onset of the glass transition temperature (670 K) for 12 h yielded transparent (～60% transmission) glass-ceramics of SrBi₂B₂O₇ (SBBO) with well defined microstructure. These were found to be textured associated with an orientation factor of about 0.77 (77%). The optical transmission studies carried out in the 100–1200 nm wavelength range confirmed both the as-quenched and heat-treated samples to be transparent from 400 to 1200 nm. The dielectric properties of the as-quenched as well as the heat-treated (670 K/12 h) samples were studied as a function of frequency (100 Hz–10 MHz) at various temperatures (303–873 K). The dielectric dispersion at higher temperatures in the as-quenched glass was rationalized using Jonscher’s dielectric dispersion relations. The prefactor A(T) and the exponent n(T) in the Jonscher’s expression were found to be maximum and minimum respectively around the crystallization temperature (T_cr) of the as-quenched SBBO glasses.