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.     

Structurization of a solvent interacting with fullerene C<Subscript>60</Subscript>

Solutions of fullerene C₆₀ in toluene and p-xylene were investigated by small-angle X-ray diffraction. In all small-angle scattering curves, the scattering intensity decreases to constant value I_C with an increase in the scattering angle. The value of I_C nonmonotonically depends on the fullerene concentration. The radii of gyration of scattering elements were determined by constructing small-angle X-ray diffraction patterns in Guinier coordinates.     

Small-angle X-ray scattering study of the structure of powder fullerene C<Subscript>60</Subscript> and fullerene soot

Powder samples of fullerene C₆₀ and fullerene soot have been studied by the small-angle X-ray scattering method. The radii of gyration of scattering elements have been determined by constructing small-angle diffraction patterns in Guinier coordinates. The data obtained agree well with the results of wide-angle X-ray scattering study, the available data on the structure of the powder fullerene C₆₀ prepared by the Huffman-Krätschmer technique, and the structure of the C₆₀ molecules. Conglomerates of two C₆₀ molecules, along with crystallites ～20 nm in size that are distributed in an amorphous matrix, are present in fullerene powders. Fullerene soot contains C₆₀ crystallites 20–25 nm in size and graphite crystallites ～2–3 nm in size that are distributed in an amorphous matrix.     

Bi20TiO32 nanocones prepared from Bi–Ti–O mixture by metalorganic decomposition method

Bi₂₀TiO₃₂ in the form of nanocones are reported for the first time, which have been found during the formation of Bi₂Ti₂O₇ nanocrystals. Bi₂₀TiO₃₂ nanocones were prepared by metalorganic decomposition technique. From X-ray patterns, it was found that Bi₂₀TiO₃₂ is a metastable phase, and can transform gradually into Bi₂Ti₂O₇ phase with the annealing time increasing at a temperature of 550°C. The image of field emission scanning electron microscopy shows that the lengths of the nanocones are up to several micrometers and the diameters of cusps range from 20 to 200 nm. The studies of transmission electron microscopy show that the nanocones are crystalline Bi₂₀TiO₃₂. The growth mechanism of Bi₂₀TiO₃₂ nanocones has been proposed, which is similar to the vapor–liquid–solid growth mechanism.     

A comparison of the medium-range order in glassy GeS2 and Sb2S3

In amorphous (a-) GeS₂ there is only one medium-range order (MRO) dependent X-ray scattering feature, i.e., the ‘first sharp diffraction peak’ (FSDP), whereas in a-Sb₂S₃ all scattering features in the interval 1–2.4 Å⁻¹ are in fact MRO-dependent. The basic element of MRO in a-GeS₂ is a part of a chain of corner bound tetrahedra extracted from the high temperature form of c-GeS₂; in a-Sb₂S₃ it is a part of a crystalline-like (Sb₂S₃)_n band. Ordering of parts of these bands is characterized by a greater interband separation than in the crystal. By contrast with a-GeS₂, the MRO-dependent medium-angle scattering features in a-Sb₂S₃ are less sensitive to fluctuations of the interband (intercluster) ordering distance.     

A SAXS study of the gelation process of silicon and titanium alkoxides

The gelation process of silicon ethoxide and titanium iso-propoxide solutions was studied as a function of water content and reaction time by small-angle X-ray scattering (SAXS). Approaching the gelation points, the SAXS intensities for titanium tetra-iso-propoxide solutions start to follow a power-law decay in the Porod region, except for a H₂O/Ti ratio greater than 4. For silicon ethoxide solutions, the fractal dimension, d_f, measured for aggregated clusters increases continually with the H₂O/Si ratio and can be related to the spinnability of the solutions. For solutions of both silicon and titanium alkoxides, a solution of fractal dimension d_f < 1.79 shows spinnability, whereas solutions having d_f > 1.79 and no fractal structures do not show spinnability.     

A SAXS study of V2O5·nH2O sols and gels

Small-angle X-ray scattering (SAXS) measurements on V₂O₅·nH₂O sols and gels, prepared by dissolving V₂O₅ glass into water at room temperature, show that there are V₂O₅ polymeric fibers entangled like random coils in the sol of n 5000, while the deviation from the random coil behavior occurs in the dilute sol of n 6000.

A Bragg peak appears at the scattering vector h 0.02 Å⁻¹ to be superimposed on an asymptotic h⁻²-course in the SAXS curve of the concentrated sol of n 680. This means that the spatial correlation between V₂O₅ polymeric fibers takes place even in the fluid state.

V₂O₅·nH₂O sols completely lose fluidity at n 250 to transfer to the gel state, where V₂O₅ polymeric fibers begin to pile up in the parallel with a substrate surface. Such a layer structure is preserved up to the gel of n 4. However, V₂O₅ polymeric fibers are randomly oriented within each layer.     

An anomalous X-ray structural study of an amorphous La55Al25Ni20 alloy with a wide supercooled liquid region

The atomic structures of amorphous La₅₅Al₂₅Ni₂₀ alloys which have a wide supercooled liquid region and a high reduced glass transition temperature have been studied using anomalous X-ray scattering (AXS) at the Ni K-absorption edge as well as the ordinary X-ray diffraction with Mo K radiation. The interference functions and the radial distribution functions were determined for the amorphous alloys as-quenched and after annealing at various temperatures and also for a fully crystallized sample. These systematic structural studies revealed a drastic change in Ni environment upon crystallization. The need for such atomic rearrangements around the Ni atoms during crystallization may be the reason why the amorphous phase is thermally stable.     

Structural changes of amorphous Pd80Si20 with neutron irradiation,with an interpretation in terms of the imperfections in the structure of amorphous solids

Wide and small-angle X-ray scattering measurements were made, as well as differential scanning calorimetry, for amorphous Pd₈₀Si₂₀ before and after irradiation by neutrons (5 × 10²⁰ neutrons/cm², > 1 Mev), and the structural changes thereby produced are described.Before irradiation the structure is well assimilated with a dense random packing (DRP) structure except that the coherence between neighboring Pd atoms extends farther than expected from the DRP structure, the coherent length estimated from the X-ray scattering being about 8 Å.With irradiation the coherent regions of 8 Å diameter get separated from each other by a mean distance of 20 Å, thus producing structural inhomogeneities which do not exist at all before irradiation. The glass transition temperature is found to be increased by about 10 K after irradiation.The effects of irradiation are interpreted as being due to the structural imperfections produced by particle bombardment. The DPR structure is adopted as a model structure for the perfect amorphous solids.     

Processing of intensities of electron scattering from amorphous silicon by methods of continuous wavelet analysis

It is shown that intensities of electron scattering from amorphous silicon can be processed by the methods of wavelet analysis. The coordination radii for amorphous silicon at various annealing temperatures are calculated using the intensity distribution of coefficients of the wavelet transform.     

Crystallization behavior and hydrophilic performances of V2O5–TiO2 films prepared by sol–gel dip-coating

Homogeneous and transparent V₂O₅–TiO₂ composite nanometer thin films were prepared on glass substrates by sol–gel processing and dip-coating technique. The films as well as the dried powder of bulk gel were characterized by different techniques like X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM), atomic force microscope (AFM) and thermogravimetry–differential thermal analysis (TG–DTA). The hydrophilicity of the films was determined by measuring the water contact angles on the films. The results showed that the dopant of V₂O₅ on TiO₂ thin films could produce a visible-light response to the films, and the introduction of V₂O₅ could suppress the structural phase transition and crystal growth of TiO₂ crystal. Finally, the relationship between crystalline size and hydrophilicity under sunlight was investigated in this article.     

RDF analysis of structural evolution during the primary crystallization of the Fe40Ni38Mo4B18 glassy alloy

The changes in the atomic structure of amorphous Fe₄₀Ni₃₈Mo₄B₁₈ during the crystallization process were studied by X-ray diffraction. The radial distribution functions of various specimens frozen at significant points of the relative DSC thermograms, were obtained from the interference functions by means of the usual Fourier analysis.

It appears from the results that the onset of crystal formation implies the simultaneous occurrence of atomic rearrangements involving the basic structural units already present in the unannealed sample; a five-fold symmetry and icosahedral structure were found for these units. An effort was made to correlate the progress in the crystalline organization with the significant features of the DSC related thermograms.     

The short-range order in ternary ZrF4---BaF2---ErF3 glasses

The short-range order structures in ternary ZrF₄---BaF₂---ErF₃ glasses have been studied by X-ray absorption fine structure (XAFS). The near-neighbor structures around Zr, Ba and Er have been determined and compared with that in binary ZrF₄---BaF₂ glasses. The near-neighbor structures around Zr and Ba are scarcely affected by doping with ErF₃. The structural parameters of near neighbors around Er in the glasses are near to that in ErF₃, but the corresponding distance and coordination number of near neighbors in the glasses decrease slightly. It is also observed that the intensities of the white lines at the Er L and L absorption edges in these glasses are different from that in c-ErF₃. Meanwhile, compared with that of the corresponding fluoride, the changes of the ‘white line’ at the Er L_,-edges in the glasses differ from the case of Nd. The causes leading to these differences are discussed.     

SAXS investigations of structure of formation in alcoholic ZrO2---SiO2 solutions

Small-angle X-ray scattering was used to examine in situ formation of ZrO₂---SiO₂ structures in alcoholic solution of tetraethoxysilan (TEOS) as a function of the ratio of ZrO₂ to SiO₂. For the moment of the first measurement (15 min after the preparation) primary particles with R_g ≈ 1.5 nm exist in all investigated mixed gels. These particles aggregated to secondary clusters. The resulting clusters can be described by means of fractal theory, where the determining mechanism of formation is cluster-cluster aggregation (diffusion or chemical limited). The time of gelation is a function of the ZrO₂ concentration. The higher the ZrO₂ concentration in the solution, the faster is the aggregation to secondary clusters. Gelation times were between 170 and 970 h.     

ZrO2-SiO2 materials prepared by sol-gel

Gels with composition xZrO₂−(100−x)SiO₂, X = 10−55, were prepared in different conditions using zirconium acetylacetonate and TEOS as precursors.

Gels treated at different temperatures up to 1100°C were characterized by X-ray diffraction, IR spectroscopy and TEM. Preparation conditions determined the subsequent development of crystalline phases following thermal treatment.

Monoclinic zirconia segregation dispersed in a silica matrix occurred when the gels were prepared in a strong hydrocloric acid medium. Preparation with a lower acid content favours instead the formation of very small crystals of tetragonal zirconia.     

Crystallization kinetics of the Zr61Al7.5Cu17.5Ni10Si4 alloy using isothermal DSC and TEM observation

The crystallization behavior and microstructure development of the Zr₆₁Al_7.5Cu_17.5Ni₁₀Si₄ alloy during annealing were investigated by isothermal differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy. During isothermal annealing of the Zr₆₁Al_7.5Cu_17.5Ni₁₀Si₄ alloy at 703 K, Zr₂Cu crystals with an average size of about 5 nm were first observed during the early stages (30% crystallization) of crystallization by TEM. The Zr₂Cu crystal size increased with annealing time and attained an average size of 20 nm corresponding to the stage of 80% crystallization. In addition, the change in particle size with increasing annealing time exhibited a linear relationship between grain growth time and the cube of the particle size for the Zr₂Cu type crystalline phase. This indicates that the crystal growth of the Zr₆₁Al_7.5Cu_17.5Ni₁₀Si₄ alloy belongs to a thermal activated process of the Arrhenius type. The activation energy for the grain growth of Zr₂Cu is 155 ± 20 kJ/mol in the Zr₆₁Al_7.5Cu_17.5Ni₁₀Si₄ amorphous alloy. The lower activation energy for grain growth in compared to that for crystallization in Zr₆₅Cu₃₅ 440 kJ/mol crystal corresponds to the rearrangement of smaller atoms in the metallic glass, Al or Si (compare to Zr).     

The electrical, optical and crystalline properties of GaAs: C grown by GSMBE using TMG and AsH3 for application to HBTs

We report the results of a comprehensive study on the electrical, optical and crystalline properties of heavily carbon doped p-type (100) GaAs epilayers (p = 6.3 × 10¹⁸−1.3 × 10²⁰ cm^-3; THICKNESS = 250−420 nm) grown by gas source molecular beam epitaxy using trimethylgallium and arsine. X-ray analysis showed epilayer lattice contraction with a mismatch of δa/a = -1.8 × 10^-3 at p = 1.3 × 10²⁰ cm^-3. Room temperature photoluminescence peak energy shifted from 1.40 eV (p = 6.3 × 10¹⁸ cm^-3) to 1.37 eV (p = 1.3 × 10²⁰ cm^-3). Stokes Raman spectra showed two modes assigned as the unscreened LO phonon (292 cm^-1) and the low frequency branch of the coupled hole-plasmon-LO-phonon (266 cm^-1). Conservation of Raman scattering rules under all incident light configurations showed that the (100) GaAs:C epilayers were of high crystalline quality without the presence of faceting or other such crystalline defects. Annealing at 900°C for between 30 s to 45 min, resulted in a significant reduction in the hole concentration, lattice contraction and photoluminescence intensity for all epilayers. The implications of these results for the development of GaAs/AlGaAs HBTs are discussed.     

Crystallization kinetics of (Ni0.75Fe0.25)78Si10B12 amorphous alloy

Amorphous ribbon specimen of (Ni_0.75Fe_0.25)₇₈Si₁₀B₁₂ has been prepared by a single roller melt-spinning technique in the air atmosphere. The crystallization kinetics of the alloy has been investigated using different thermal analysis by means of continuous heating and isothermal heating. The activation energy of the alloy has been calculated by using Kissinger plot method and Ozawa plot method based on differential thermal analysis data, respectively. The products of crystallization have been analyzed by X-ray diffraction. A single phase of γ-(Fe, Ni) solid solution with grain size of about 10.3 and 18.5 nm precipitates in the amorphous matrix after annealing at temperatures 715 and 745 K, respectively. The crystallized phases are γ-(Fe, Ni) solid solution, Fe₂Si, Ni₂Si, Fe₃B and unidentified phase after annealing at 765 K. The details of nucleation and growth during the isothermal crystallization are expatiated in terms of local Avrami exponent and local activation energy.     

Al2O3-TiO2 and Al2TiO5 ceramic materials by the sol-gel process

Ceramic materials with a very low thermal expansion coefficient are synthesized by the sol-gel process. The binary gel is obtained by hydrolysis and polycondensation reactions of organometallic compounds of aluminium and titanium. The thermal evolution of the amorphous powder is followed by DTA and TGA measurements. Structural evolution is followed using X-ray diffraction. The crystallization of the TiO₂ rutile and Al₂O₃ corindon starts at 700 and 900°C respectively. The transformation of Al₂O₃ and TiO₂ into Al₂TiO₅ appears between 1200 and 1300°C. The densification of the powder is performed by the hot pressing process. The shrinkage of the powder was previously followed by dilatometric measurements. The physical properties of the final material are studied as a function of pressing parameters.     

A thermodynamic and kinetic investigation of amorphous (1−x)As2Se3 · xSb2Se3 alloys

The heats of formation of amorphous (1?x)As₂Se₃ · xSb₂Se₃ (x = 0 to 0.4) referred to crystalline As₂Se₃ and Sb₂Se₃ were measured by liquid metal solution calorimetry. The values of heats of formation of amorphous (1?x)As₂Se₃ · xSb₂Se₃ decreased from 1.39 ± 0.03 kcal · (g-at)^?1 at x = 0 to 1.27 ± 0.04 kcal · (g-at)^?1 at x = 0.4.The glass transition temperature and the temperatures of the maximum rates of crystallization and fusion were measured by differential scanning calorimetry. The glass transition temperature increased and the temperatures of the maximum rates of crystallization and fusion decreased with increasing Sb₂Se₃ content.The relaxation process in amorphous (1?x)As₂Se₃ · xSb₂Se (x = 0.3) was investigated by measuring changes in microhardness, small-angle X-ray scattering and heat capacity with time of annealing at several temperatures ranging from room temperature to 413 K. With increasing annealing time the microhardness, the height and the temperature of the glass transition peak increased whereas the intensity of small-angle X-ray scattering decreased. These changes reflect relaxation towards a more stable structure of smaller molecular mobility. The changes in the enthalpy with annealing time and the activation energy spectra for relaxation were derived from the heat capacity data. The effects of temperature and time of annealing on the various properties are explained in terms of structural changes and relaxation kinetics.