Influence of alumina addition on crystallization and texturing behavior of LaBGeO5 glass

The structure and crystallization behavior of glasses with 25La₂O₃ · 25B₂O₃ · 50GeO₂ composition, melted in platinum (P glass) and corundum (A glass) crucibles, were studied by DTA, X-ray diffraction and FTIR spectroscopy. The Al₂O₃ dissolved from corundum crucible in the A glass was estimated to be in the range 5–7 wt%. This alumina content had almost no influence on glass transition temperature but strongly affected the structure and crystallization behavior of the A glass. In fact, the P glass showed good texture-forming ability: high quality textured glass-ceramic plates based on stillwellite-like LaBGeO₅ crystals were easily obtained. On the contrary, the presence of alumina stabilized the A glass from which binary phases crystallize first, and only afterwards they are transformed in stillwellite by secondary crystallization: so in this glass texturing is hindered. Crystallization and texturing behavior of P and A glasses were well related to FTIR data. P glass contained both threefold and fourfold coordinated boron while in the A glass the presence of aluminum forced boron to assume almost exclusively threefold co-ordination. Hence the easier crystallization of stillwellite phase and the good textures obtained from the P glass contrary to the A glass, can be well understood since all boron atoms have tetrahedral co-ordination in stillwellite LaBGeO₅ crystal.     

The effect of mechanical instability on crystallization rate in czochralski growth system

The effect of mutual displacement of crucible and crystal or melt level change on crystallization rate is described in one-dimensional heat-transfer approximation. It is found that Czochralski growth system is very sensitive to mechanical instability and crystallization rate follows the jitter pattern. As an example crystallization rate behaviour is examined for fluorite and silicon crystal growth.     

Electrical and optical properties of binary glasses from the arsenictelluriumselenium system

An investigation of binary glasses derived from the arsenicseleniumtellurium system is described in which measurements were made of d.c. conductivity over a range of temperatures, space charge limited current, density and absorption in the near infrared region. For the higher temperature region the electrical results were consistent with conduction being due to carriers excited into extended states. While conduction at lower temperatures may in some cases be due to carriers hopping in localized states at the band edges, an alternative approach in which the localized states were considered to act as donors and acceptors gave satisfactory agreement with the experimentally determined conductivity versus temperature and activation energy versus temperature relationships and with the value of the pre-exponental constant in the conductivity expression. An anomalous field dependence of conductivity was found for annealed specimens of two glasses and it is tentatively suggested that this is associated with the creation of an impurity band. Measurements of space charge limited current showed that gold gave ohmic contacts to the glass, whereas silver and copper did not. The measurements also provided evidence for the localized states having an exponential distribution. Changes of electrical properties and density as a function of glass composition are discussed in the light of possible structural changes taking place in the glasses. The absorption edges of the glasses in the infrared region were found to be exponential in form and had slopes that did not very greatly for the range of compositions studied.     

Effect of frit size on sintering, crystallization and electrical properties of wollastonite glass-ceramics

Wollastonite glass-ceramics were prepared through pressureless sintering. The sinterability of the prepared samples of the glassy powder in the system (SiO₂-CaO-Na₂O-Fe₂O₃-WO₃) was investigated in the temperature range 720-900 °C and soaking time of 180 min. The influence of the increase in the glass powder particle size on the sinterability and dielectric properties of the glass-ceramic samples was studied.The sintered specimens were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. XRD analysis revealed that wollastonite was the main crystalline phase in the sintered glass-ceramics. Dielectric properties such as dielectric constant and dielectric loss were measured via a network analyzer at 10 GHz.It was observed that the increase of the glassy powder particle size improved the sinterability and dielectric properties of the glass-ceramic specimens. Wollastonite glass-ceramics with 16 μm particle size had maximum constant and minimum loss (ε_r = 10.10 and tan δ = 0.005) compared with the other glass-ceramics.     

The effects of As and Te on the crystallization and optical gaps of selenium

Glasses with compositions Te_xSe_100−x (0x25 at.%), As_ySe_100−y (0y40 at.%) and As₂Te_zSe_98−z (0z25 at.%) were prepared. The effects of the additives As and Te on the crystallization behaviour and optical gaps of selenium were studied. The relationship between the above properties and the chemical bond nature of the glass constituents is discussed. Materials with long lifetime and high sensitivity can be obtained by the addition of certain amounts of As and Te into Se.     

The effect of alloying elements on the crystallization behaviour and on the properties of galvanized coatings

The influence of the alloying elements on the interface reactions of zinc coatings during the galvanization process was examined. These reactions affect the crystallization and the structure and properties of the outer layer of the coatings. Depending on the type and concentration of the alloying additions in the galvanizing bath differences were induced in the crystallization process of the Fe‐Zn phases. It was found that both the concentration and the distribution of the alloying elements played an important role in the growth of the phases. The formation of the phases and the distribution of the alloying elements in the coatings were determined using X‐Ray diffraction (XRD) and Scanning Electron Microscopy (SEM) associated with an Energy Dispersive X‐Ray Spectroscopy (EDS) analysis. Finally the behaviour of the galvanized coatings was examined under accelerated salt spray corrosion conditions. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of copper ions addition on structural and optical properties of zinc borate glasses

Glasses in the ternary system xCuO?(100 ? x)[55B₂O₃·45ZnO] (0 ≤ x ≤ 20 mol%) have been prepared by melting at 1200 °C and rapidly cooling at room temperature. The effect of copper ions addition in 55B₂O₃·45ZnO glass matrix together with the matrix effect on paramagentic behavior has been investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, differential thermal analysis (DTA), electron paramagnetic resonance (EPR), ultraviolet–visible (UV–VIS) spectroscopy and density measurements. The increase of the number of non-bridging oxygen (NBO) atoms as a function of CuO content in these glasses leads to the decrease of glass polymerization which reduces the stability of the glasses and favors the association of copper ions in clusters. This leads to the major changes of structural and optical properties of the studied glasses as can be seen from the data obtained by FTIR and EPR spectroscopies.     

The effect of rapid early growth on the physical and electrical properties of heteroepitaxial silicon

In an effort to optimize the semiconducting properties of heteroepitaxial silicon films less than 1 μm in thickness a procedure has been employed in which the substrate surface is covered at a rate in excess of 5 μm/min, and the remainder of the deposit is grown at a rate of 0.3 μm/min. The rapid surface coverage influences the crystallographic and electrical properties of the silicon within 0.9 μm of the sapphire substrate. Correlations are observed between X-ray diffraction profile half-widths, reflection electron (high-energy) diffraction, device mobilities and life time. The distance from the substrate over which aluminum contamination decreases to a constant bulk value, as measured by secondary ion mass spectrometry, is in good agreement with the thickness at which complete surface coverage is realized.     

The effect of Ag2O doping and crystallization on the properties of lead–vanadate glass

The mechanical and electrical properties of three lead–vanadate glass samples, namely the conventional (regular) lead–vanadate glass, the silver oxide doped variety and the doped glass containing nanocrystalline structures developed on heating have been studied. It is found that the nanostructured ceramic has its mechanical properties enhanced in comparison with those of the conventional or doped glasses. The I–V profiles of the lead–vanadate and the doped glasses manifest ohmic behavior, while a pronounced hysteresis loop is conspicuous in the case of the nanostructured glass sample. The mechanism of conduction in the lead–vanadate glass and the effect of doping with silver oxide as well as the nanocrystalline structure generation have been investigated in detail.     

The effect of diluting crystallization droplets on protein crystallization in vapor diffusion method

In this study, effects of diluting either protein or crystallization agents in the droplets on the success rate of protein crystallization was investigated. Diluting the crystallization agent was found to increase the success rate of protein crystallization. Theoretical analysis showed that, concentration ranges of both protein and crystallization agent that can be scanned during the vapor diffusion process are wider with diluting the crystallization agent than that without dilution, resulting in more opportunities for the crystallization solution to be in the nucleation zone. On the other hand, diluting protein could lead to controversial results depending on the location of the initial concentration relative to that of the nucleation zone in the phase diagram. The method of diluting the crystallization agent is therefore proposed as an alternative modification to the conventional vapor diffusion method for obtaining more crystallization conditions in protein crystallization screening. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of Ge addition on the optical and electrical properties of eutectic Sb70Te30 films

The aim of this work is to study the influence of Ge addition on the optical and electrical properties in eutectic SbTe thin films (with the compositions: Sb₇₀Te₃₀, Ge₂Sb₇₀Te₂₈, Ge₅Sb₇₀Te₂₅ and Ge₁₀Sb₆₅Te₂₅) using visible optical reflectance, ellipsometry measurements, near infrared transmittance spectra, and four probe electrical resistivity measurements. From near infrared transmittance measurements the optical band gap was determined using Tauc’s expression for amorphous materials, a value of about 0.47 eV was obtained without any clear dependence on the Ge content. All amorphous films have approximately the same reflectance value, however the contrast ratio between the crystalline and amorphous phases decrease with increase of Ge. Using in situ four probe measurements versus temperature the dependence of the activation energy of conductance and the onset of the crystallization temperature have been determined for different materials. Four probe measurements have shown that the resistivity of amorphous films increases with increase of Ge. The results obtained have shown that optical and electrical properties of SbTe films with near eutectic composition change with the Ge content and depending on the application, in either optical or electrical memory devices, the most suitable composition needs to be determined.     

Photoelectronic and electrical properties of CuIn5S8 single crystals

To identify the impurity levels in CuIn₅S₈ single crystals, the dark electrical conductivity and photoconductivity measurements were carried out in the temperature range of 50–460 K. The data reflect the intrinsic and extrinsic nature of the crystals above and below 300 K, respectively. Energy band gaps of 1.35 and 1.31 eV at 0 K and 300 K, were defined from the dark conductivity measurements and the photocurrent spectra, respectively. The dark and photoconductivity data in the extrinsic temperature region reflect the existence of two independent donor energy levels located at 130 and 16 meV. The photocurrent‐illumination intensity dependence (F) follows the law I_phαF^γ, with γ being 1.0, 0.5 and 1.0 at low, moderate and high intensities indicating the domination of monomolecular, bimolecular and strong recombination at the surface, respectively. In the intrinsic region and in the temperature region where the shallow donor energy level 16 meV is dominant, the free electron life time, τ_n, is found to be constant with increasing F. In the temperature region 140 K < T < 210 K, the free electron life time increases with increasing illumination intensity showing the supralinear character. Below 140 K, τ_n decrease with decreasing illumination intensity. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Annealing effect on electrical and photoconductive properties of Si implanted GaSe single crystal

GaSe single crystals grown by Bridgman method have been doped by ion implantation technique. The samples were bombarded in the direction parallel to c‐axis by Si ion beam of about 100 keV to doses of 1 × 10¹⁶ ions/cm² at room temperature. The effects of Si implantation with annealing at 500 and 600 °C on the electrical properties have been studied by measuring the temperature dependent conductivity and photoconductivity under different illumination intensities in the temperature range of 100–320 K. It is observed that Si implantation increases the room temperature conductivity 10⁻⁷ to 10⁻³ (Ω‐cm)⁻¹ depending on the post annealing temperature. The analysis of temperature dependent conductivity shows that at high temperature region above 200 K, the transport mechanism is dominated by thermal excitation in the doped and undoped GaSe samples. At lower temperatures, the conduction of carriers is dominated by variable range hopping mechanism in the implanted samples. Annealing of the samples at and above 600 °C weakens the temperature dependence of the conductivity and photoconductivity. This indicates that annealing of the implanted samples activates Si‐atoms and increases structural deformations and stacking faults. The same behavior was observed from photoconductivity measurements. Hence, photocurrent‐illumination intensity dependence in the implanted samples obeys the power low I_pc ∝ Φⁿ with n between 1 and 2 which is an indication of continuous distribution of localized states in the band gap. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of high pressure on crystallization of splat-cooled V2O5

Crystallization of splat-cooled V₂O₅ under high pressure was examined. By X-ray diffraction and thermal analysis, it is shown that the non-crystalline V₂O₅ crystallizes dramatically up to about 6 kb. Crystallization temperature increases with increasing pressure under this pressure range.At higher pressure (20–60 kbar), crystallization occurs gradually and the crystallization temperature has a slight tendency to decrease with increasing pressure.     

The effect of solvents and crystallization conditions on crystal habit of cholesterol

The effect of various organic solvents as well as the crystallization conditions on the crystal habit of anhydrous cholesterol have been studied. Both plates and needle-like crystals can be obtained in a particular solvent depending on the degree of supersaturation of the solution. However, the crystals grown at about the same supersaturation, from different solvents, show differences in their habit indicating dependence on the solvent-solute interaction. Thus, it is advisable not to identify needle-like crystals with anhydrous-cholesterol and plates with mono-hydrate cholesterol without specifying the crystallization conditions. A prediction on the crystal habit length to width ratios can be made using those parameters.     

The influence of Ta2O5 additions on the thermal properties and crystallization kinetics of a lithium zinc silicate glass

The lithium zinc silicate glass exhibits two crystallization exotherms corresponding to the formation of Li₂ZnSiO₄ and silica phases, respectively. The silica phases include tridymite and cristobalite. The influence of Ta₂O₅ additions on the thermal properties and non-isothermal crystallization kinetics of this glass, including nucleation rate maxima and activation energies for crystallization, has been determined by differential scanning calorimetry and X-ray diffraction. It has been found that Ta₂O₅ affects the crystallization behavior markedly, inhibiting the crystallization of high thermal expansion silica phases at lower concentrations, whilst at higher concentrations also suppressing crystallization of the Li₂ZnSiO₄ phase. At the higher concentrations, these phases are replaced by small amounts of LiTaO₃ and LiTaSiO₅.     

The effect of initial oxidation state on crystallization of basaltic glass

Iron-rich silicates mined as basalt may be processed as glass fibers and, woven to textile mats, it may be used as heat insulation. High-temperature stability is however a limiting factor because at least three process of alteration occur upon heat treatment that affect mechanical and chemical properties, micron to nano-crystallization, oxidation and cation-enrichment at the glass surface with a few microns depth. We here evaluate the crystallization behavior of synthetic Fe³⁺-rich basalt (SB) heat treated in air (negligible oxygen potential) in comparison with previously studied Fe²⁺-rich natural basalt (NB) heat treated in air and in Ar (i.e., high and low oxygen potential, respectively). Initial crystals growing in Fe²⁺-rich basalt are micron-sized dendrites, and with temperature of heat treatment they become increasingly granular and are identified as pyroxene. Pyroxene in SB form smaller dendrites; crystallization textures and nucleation and growth rates, derived from crystal size distribution, are independent of the temperature of heat treatment in the range between 850 and 1030 °C. Here, the activation energy of pyroxene vanishes, though crystallization rates are smaller than those of NB. Whereas in NB pyroxene growth occurs diffusion limited, in SB it is likely to be limited by the attachment of ions to new crystal surface.     

The effect of sulfated polysaccharides on the crystallization of calcite superstructures

Calcite with unique morphology and uniform size has been successfully synthesized in the presence of classes of polysaccharides based on carrageenans. In the crystallization of calcite, the choice of different carrageenans, (iota, lambda and kappa), as additives concedes systematic study of the influence of different chemical structures and particularly molecular charge on the formation of CaCO₃ crystals. The uniform calcite superstructures are formed by assemblies and aggregation of calcite crystals. The mechanism for the formation of calcite superstructures was studied by a variety of techniques, SEM, TEM, XRD, time-resolved conductivity and light scattering measurements, focusing on the early stages of crystals' nucleation and aggregation.