Showing papers on "Amorphous solid published in 1975"

Structure of Metallic Alloy Glasses

Abstract: Publisher Summary Metallic glasses are solids that have electronic properties normally associated with metals, but with atomic arrangements that are not spatially periodic. Noncrystalline and amorphous are equivalent terms used to describe the atomic scale structure of such materials. The term glass has often been reserved for amorphous solids formed by continuous solidification of a liquid, but is used in this review to refer to amorphous solids produced in a variety of ways. These include evaporation, sputtering, and electro- and chemical deposition, as well as quenching from the liquid state. The current status of research on structure of metallic glasses is reviewed in this chapter. Discussion is largely limited to metallic glasses which can be retained at room temperature. All of these contain at least two atomic components. Nominally pure, elemental metallic glasses have been prepared, but their metastability depends critically on impurity content; most of these crystallize well below room temperature.

The Formation of Hematite from Amorphous Iron(III)Hydroxide

Abstract: The formation of hematite from amorphous Fe(III)hydroxide in aqueous systems at pH 6 and 70°C, both with and without oxalate, was followed by kinetic measurements, electron microscopy, i.r. spectroscopy and thermal analysis. In the absence of oxalate, small amorphous particles coalesce into aggregates which eventually become single crystals of hematite. When oxalate is present, crystal growth is much faster and does not proceed through the intermediate stage of aggregation. Aggregates, when formed, consist of groups of single crystals. It is suggested that oxalate accelerates the nucleation of hematite crystals by acting as a template, the Fe-Fe distance in Fe-oxalate ions being similar to that in hematite.

Dependence of diffusive transport on morphology of crystalline polymers

Abstract: The sorption and diffusion of low molecular weight penetrants proceeds almost exclusively through the amorphous component of the semicrystalline polymer solid. The diffusive transport properties and geometrical distribution of the amorphous component are substantially modified by mechanical and thermal treatment. Deformation of spherulitic material first loosens the structure and then transforms it into a densely packed fibrous structure with a great many taut tie molecules in the amorphous component. Annealing lets the crystals grow in thickness, removes crystal defects, sharpens the boundaries between crystalline and amorphous component, and relaxes the taut tie molecules. The resulting changes of transport properties cannot be described in a satisfactory manner by crystallinity and orientation but requite a detailed consideration of morphology. The elastic tensile deformation enhances sorption and diffusion by reducing the density of amorphous component. The high anisotropy of diffusion and th...

Model for the bleaching of WO3 electrochromic films by an electric field

Abstract: Measurements have been made of the current flow in amorphous WO3 films containing electrons and mobile cations. In a configuration in which electrons are extracted at one contact and cations at the other, the current decays as t−3/4 over many decades of time. By using space‐charge current flow ideas, we develop a theory that gives the correct time dependence and magnitude of the current for this double‐extraction phenomenon.

Devitrification characteristics of GexSe1−x glasses

Abstract: Amorphous Ge x Se 1− x compounds have been prepared and carefully characterized in the range 0 ⩽ x ⩽ 0.43 (density and micro-hardness measurements and DTA experiments). By heating samples from the amorphous phase, the crystallization process has been investigated for 0.15 ⩽ x ⩽ 0.30. An immiscibility gap in the vitreous region is determined by optical microscopy, from phase-separation observations; moreover, a new metastable crystalline phase appearing as an intermediate step between phase separation and stable GeSe 2 is described.

Transformation behavior of PdAuSi metallic glasses

Abstract: The transformation behavior of roller-quenched amorphous Pd 0.82− x Au x Si 0.18 and Pd 0.835− x Au x Si 0.165 alloys, where x ⩽ 0.10, after rapid heating to temperatures near to or above T g , is reported. The calorimetrically determined glass ( T g ) and kinetic crystallization ( T c ) temperatures both increased with x up to x ≈ 0.04. With increasing x , at x ⩾ 0.04, T c decreased rapidly while T g varied little. Binary Pd 0.82 Si 0.18 alloys crystallized to an fcc phase without apparent composition segregation. The tendency to phase separate at T near T g , as manifested by small- (SAXS) and large-angle X-ray scattering and calorimetry, increased with increasing Au substitution. Pd 0.8 Au 0.035 Si 0.165 alloy apparently phase separated by a nucleation and growth mechanism, with a growth rate limited by the melt viscosity, to form an fcc phase dispersed in an amorphous phase which later crystallized. Pd 0.74 Au 0.08 Si 0.18 alloy phase separated initially to two melts, each of which later crystallized in turn. The initial separation behavior was generally consistent with the predictions of the spinodal theory but with some deviation from Cahn's linear relation.

Photoacoustic spectroscopy of solids

Abstract: One of the most effective means for studying the properties of matter nondestructively is to observe how photons interact with it; that is, by optical spectroscopy. The two most common techniques in the optical region are absorption and reflection spectroscopy. But many organic and inorganic materials, such as powders, amorphous compounds, smears, gels and oils, can not be readily studied by either of these two techniques. Methods involving diffuse or attenuated total reflectance permit the study of some of these materials, but they possess severe drawbacks.

Electronic structure of trigonal and amorphous Se and Te

Abstract: The electronic structure of trigonal and amorphous Se and Te is investigated using the empirical pseudopotential method (EPM), charge-density calculations, and simple tight-binding models. Band structures and electronic densities of states are obtained which are in excellent agreement with recent photoemission measurements. The tight-binding models are used to obtain analytic expressions for the energy bands and to interpret the EPM band structures in terms of real-space orbital-orbital interactions. Charge-density calculations obtained as a function of energy and evaluated within specific energy intervals are used to interpret various structure in the density of states. Specifically certain easily resolvable peaks in the experimental photoemission spectra are associated with intrachain and interchain localized states, respectively. By taking only short-wavelength components of the charge density, a bonding charge can be defined which gives an estimate of the intrachain vs interchain bonding strengths. The trigonal results along with model calculations to investigate the effects of bond-angle variations on chains and the presence of eight- and six-fold rings of bonds are used to interpret the changes observed in the experimental spectra of amorphous Se and Te. A new model of amorphous Se is proposed.

Deformation and fracture of an amorphous metallic alloy at high pressure

Abstract: The influence of hydrostatic pressure (∼ 6.5 kbar) on the stress for plastic flow in a Pd77.5Cu6Si16.5 amorphous metallic alloy in compression and tension has been examined. The observed effect (δlnσ/δP ∼- 5×10−6 bar−1) is very close to that exhibited by crystalline metals. The highly inhomogeneous nature of the deformation appears to be unaltered by pressure. As at one atmosphere, failure in tension with high superposed pressure occurs by rupture through a zone of intense plastic shear. The fracture surface topography is strikingly different, however, because cracking inside the shear zone is suppressed in favour of crack initiation at its periphery.

Mechanism of electrochromism in WO3

Abstract: X‐ray photoelectron spectra of colored WO3 films, thermodynamic analysis of galvanic behavior of the tungstic oxide cathode, plus other new lines of evidence, clearly establish the previously uncertain mechanism of the electro‐optic effect in amorphous WO3, viz., a simultaneous injection of electrons and positive ions into a film via an electrochemical process, with the consequent development of a low‐x tungsten bronze. The positive ion, in both the films and in tungsten bronzes, remains fully ionized even in the presence of high densities of injected electrons.

Direct comparison of ion−damage gettering and phosphorus−diffusion gettering of Au in Si

Abstract: The residual disorder caused by different implanted ions after annealing at elevated temperatures (850−1150 °C) is dependent upon the ion species. The gettering of Au by damaged layers produced by Ar, O, P, Si, As, and B has been quantitatively compared to gettering by phosphorus diffusion. Each individual comparison was made between opposite surfaces of a Si sample by use of Rutherford backscattering. The damage disorder was quantitatively measured by backscattering and structurally studied using electron microscopy. Typically, an ion dose of 1016/cm2 and ion energy of 200 keV were used for implantations. The Au was present in the Si at ’’moderate’’ levels so that solubility in the phosphorus diffused layers was not exceeded. Ar ion−damaged layers were more effective for gettering Au than were phosphorus−diffused layers below ∼1000 °C and equally effective up to 1150 °C. The relative gettering efficiency of the damage produced by other ions studied was less than that of phosphorus diffusion at 1000 °C and was ranked in the order Ar≳O≳P≳Si≳As≳B. In general, the relative gettering efficiency of ion−damaged layers was related to the amount and type disorder after annealing. The initial disorder was of an amorphous nature for 1016 heavy ions/cm2 (As, Si, P, Ar, or O), and the final disorder state was different for different implanted ions after annealing. It is suggested that the disorder (and gettering efficiency) was influenced by size effects of the implanted ion during annealing.

Concentration profiles of boron implantations in amorphous and polycrystalline silicon

Abstract: Boron was implanted in amorphous silicon at energies in the range 30–200 keV and in polycrystalline silicon at energies in the range 70–800 keV. The boron distributions were measured with secondary ion mass spectrometry. By comparing the boron distributions in amorphous silicon and in polycrystalline silicon it was found that the used polycrystalline silicon behaves similarly to amorphous silicon for the boron stopping process. It was found that with the first four moments of the experimental distributions, an analytic description of the experimental distributions can be given by distributions of the Pearson system. The moments are determined by curve fitting of Pearson distributions to experimental distributions. In this way a systematic extrapolation of the low energy distributions outside the surface is automatically obtained. The moments are compared with the moments calculated by Winterbon and others. A satisfactory correspondence between the experimental and theoretical average ranges and s...

Metallic glasses as relaxed Bernal structures

Abstract: A dense random packing of 888 hard spheres has been relaxed with respect to a realistic interatomic potential. The result is compared to the experimental pair distribution function of amorphous Co and an amorphous Ni76P24 alloy. The positions of the maxima of the pair distribution function of Co are accurately reproduced. The differences between Co and Ni76P24 are discussed.

Measurement of the diffusion coefficient of electrons in WO3 films

Abstract: Measurements of the electron diffusion coefficient in amorphous films of tungsten oxide give a value of D=0.0025±0.0006 cm2 sec−1. D decreases by less than a factor of 2 between +40 and −20 °C.

Studies on physical properties and structure of silk. Glass transition and crystallization of silk fibroin

Abstract: Amorphous silk fibroin with random coil conformation shows endothermic and exothermic peaks and endothermic shift on the DSC (differential scanning calorimetry) curve. The endothermic shift observed at 175°C was due to the glass transition. The exothermic peak at 212°C is recognized to be the crystallization, which later was confirmed by x-ray diffraction pattern. The endothermic peak at 280°C is shown to be the degradation.

Obliquely deposited amorphous Ge films. I. Growth and structure

Abstract: The structure and growth of amorphous Ge films deposited at an angle of incidence ranging from 0° to 80° have been studied by electron microscopy and electron diffraction as a function of the film thickness, deposition temperature, deposition rate, and annealing temperature. Like crystalline films, the growth of amorphous films proceeds via random nucleation centers and is controlled by the small but finite adatom mobility. The small adatom mobility results in the formation of a large concentration of vacancies, vacancy clusters, voids, and associated dangling bonds in a‐Ge films. The adatom mobility is enhanced by the elevated deposition temperatures and oblique incidence and, consequently, the concentration of vacancy clusters and voids decreases. The formation of columns and decoration of structural defects associated with the cleaved NaCl single‐crystal substrates during the growth of a‐Ge films are a direct consequence of the enhanced adatom mobility. The observed thickness dependence of the resistiv...

The glass point of elastin.

Abstract: Elastin undergoes a glass transition in a temperature range depends on its water content. This behavior is similar to that of amorphous polymers swollen with solvent and, therefore, is additional evidence for the random network model proposed for the structure of elastin.

In situ observations of crystalline oxide formation during aluminum and aluminum alloy oxidation

Abstract: Anin situ morphological study of the oxidation of electron transparent specimens of aluminum and aluminum alloys containing zinc and magnesium has been carried out in the temperature range 400 to 520°C using the hot stage of a 1 MeV transmission electron microscope. The structure and morphology of the crystalline oxide produced in each alloy has been carefully examined by selected area electron diffraction and stereomicroscopy. In pure aluminum, oxidation takes place after a temperature dependent induction period, by the nucleation of crystalline γ-Al2O3 at the amorphous oxide/metal interface. This process is delayed by additions of zinc which modify the structure of the oxide. In alloys containing magnesium, oxidation takes place by the rapid nucleation and growth of MgAl2O4 or MgO, with a secondary form of magnesia developing from the reduction of the amorphous γ-Al2O3 surface layer.

Diffusion in the amorphous phase of Pd-19-at.%-Si metallic alloy

Abstract: Diffusion of ${\mathrm{Ag}}^{110m}$ radioactive tracer has been measured in amorphous Pd-19-at.%-Si specimens characterized by a Seeman-Bohlin x-ray diffractometer. The diffusion parameters in this metallic amorphous phase have been found to have a regime distinctly different from liquid and crystalline phases.

The transformation of amorphous silica to crystalline silica under hydrothermal conditions

Abstract: Hydrothermal syntheses were made mainly in the binary system SiO2-H2O in a temperature range between 300 ° C and 500 ° C and pressures from 0.2 kbar up to 4.0 kbar with various starting materials. In this way the transformation behavior of different amorphous silicas via cristobalite and keatite to quartz were observed. This behavior depends mainly on the parameters: pressure, temperature, run duration and state of the starting material. Four reaction paths have been observed: in most experiments the complete reaction sequence “amorphous silica→cristobalite→keatite→quartz” took place. Less often the reactions: “amorphous silica→cristobalite→quartz” and: “amorphous silica→keatite→quarts” were observed. Very few samples were found with a direct transition of amorphous silica into quartz at high pressures. A kinetic model is given in form of a pressure-temperature-time diagram of the system SiO2-H2O under hydrothermal conditions.

The Magnetic Moments of Amorphous Metal-Metalloid Alloys

Abstract: The reduction of magnetic moments of 3d transition metal atom in amorphous metal-metalloid alloys is simply interpreted by means of the electron transfer from metalloid atoms to the hole of 3d metal atoms.

The pressure and temperature effects on brittle‐to‐ductile transition in PS and PMMA

Abstract: : Tensile experiments in polystyrene (PS) and poly(methyl methacrylate) (PMMA) conducted at constant strain rate over a wide range of pressure and temperature have shown that a brittle to ductile transition is induced in these amorphous polymers by the superposition of hydrostatic pressure as well as by the raise of the experimental temperature. A detailed stress-strain analysis permits explanation of the mechanism for the brittle to ductile transition in terms of interaction between two competing processes of plastic yielding -- crazing and shear banding phenomena. The crazing and shear banding processes respond quite differently to changes of pressure or temperature. The evidence that the brittle to ductile transition pressure becomes lower with increasing temperature refutes a previously suggested concept that the transition relates primarily to mechanical relaxation phenomena.

Superconductivity at very strong coupling

Abstract: A numerical treatment of the eliashberg equations reveals that mcmillan's equation fails for lamda>1.5. For very large lamda, tc scales as (lamda(omega2))12/, while for lamda<1.0, mcmillan's equation is reasonably accurate. The authors give a new approximate tc equation which satisfies these limits, and show that the maximum tc occurs at infinite lamda. A new tunnelling measurement for amorphous pb0.45bi0.55 gives lamda=2.59 and a tc in excellent agreement with numerical solutions.