Crystallization behavior of (GeS2)0.1(Sb2S3)0.9 glass

The crystal growth kinetics of antimony trisulfide in (GeS₂)_0.1(Sb₂S₃)_0.9 glass has been studied by microscopy and DSC. The linear crystal growth kinetics has been confirmed in the temperature range 492 ? T ? 515 K (E_G = 405 ± 7 kJ mol⁻¹). The applicability of standard growth models has been assessed. From the crystal growth rate corrected for viscosity plotted as a function of undercooling it has been found that the most probable mechanism is interface controlled 2D nucleated growth. The non-isothermal DSC data, corresponding to the bulk sample, can be described by the Johnson-Mehl-Avrami equation.     

Structural,electrical and optical properties of SnO2 films deposited on Y-stabilized ZrO2 (1 0 0) substrates by MOCVD

SnO₂ films have been deposited on Y-stabilized ZrO₂ (YSZ) (1 0 0) substrates at different substrate temperatures (500–800 °C) by metalorganic chemical vapor deposition (MOCVD). Structural, electrical and optical properties of the films have been investigated. The films deposited at 500 and 600 °C are epitaxial SnO₂ films with orthorhombic columbite structure, and the HRTEM analysis shows a clear epitaxial relationship of columbite SnO₂(1 0 0)||YSZ(1 0 0). The films deposited at 700 and 800 °C have mixed-phase structures of rutile and columbite SnO₂. The carrier concentration of the films is in the range from 1.15×10¹⁹ to 2.68×10¹⁹ cm⁻³, and the resistivity is from 2.48×10⁻² to 1.16×10⁻² Ω cm. The absolute average transmittance of the films in the visible range exceeds 90%. The band gap of the obtained SnO₂ films is about 3.75–3.87 eV.     

Optical properties of Cr ion in lithium metasilicate Li2O · SiO2 transparent glass-ceramics

The optical properties of Cr³⁺ ions in lithium metasilicate (Li₂O · SiO₂) transparent glass-ceramics were investigated. The main crystalline phase precipitated was the lithium metasilicate (Li₂O · SiO₂) crystal. The percent crystallinity and crystalline size were ranging 65-75% and 20-35 nm, respectively. The color changes drastically to deep pink from emerald green upon crystallization. New and strong absorption bands appeared and the absorption intensity increases by about 10 times that in glass. These new absorption bands are found to be derived from Cr³⁺ ions in octahedral sites in the lithium metasilicate crystal lattice. Cr³⁺ ions substitute for three Li⁺ ions and occupy the distorted octahedral site between single [SiO₄]_n chains of lithium metasilicate crystal. The ligand field parameters can be estimated: 10Dq = 13 088 cm⁻¹, B = 453 cm⁻¹, Dq/B = 2.89 and C = 2036 cm⁻¹. The near-infrared luminescence centered at 1250 nm was not detected in the deep pink glass-ceramics unlike emerald green glass.     

The effect of composition on UV-vis-NIR spectra of iron doped glasses in the systems Na2O/MgO/SiO2 and Na2O/MgO/Al2O3/SiO2

Glasses with the compositions xNa₂O · 10MgO · (90 − x)SiO₂, 10Na₂O · xMgO · (90 − x)SiO₂, 5Na₂O · 15MgO · xAl₂O₃ · (80 − x)SiO₂, xNa₂O · 10MgO · 10Al₂O₃ · (80 − x)SiO₂, 10Na₂O · 10MgO · xAl₂O₃ · (80 − x)SiO₂, 10Na₂O · 5MgO · 10Al₂O₃ · (80 − x)SiO₂ were melted and studied using UV-vis-NIR spectroscopy in the wavenumber range from 5000 to 30 000 cm⁻¹. At [Al₂O₃] > [Na₂O], the UV-cut off is strongly shifted to smaller wavenumbers and the NIR peak at around 10 000 cm⁻¹ attributed to Fe²⁺ in sixfold coordination gets narrower. Furthermore, the intensity of the NIR peak at 5500 cm⁻¹ increases. This is explained by the incorporation of iron in the respective glass structures.     

Growth and spectroscopic characteristics of Er:YbVO4 crystal

A laser crystal Er³⁺:YbVO₄ has been grown by the Czochralski method with excellent quality. The rocking curve from the (0 0 4) diffraction plane of the as-grown Er³⁺:YbVO₄ crystal was measured and the full-width at half-maximum value was found to be 19.80 in. for the (0 0 4) face. The effective segregation coefficient of Er³⁺ was studied by X-ray fluorescence and the crystal structure was determined by means of X-ray diffraction analysis. The polarized absorption spectra and the fluorescence spectra of Er³⁺:YbVO₄ were measured at room temperature. The spectral parameters were calculated based on the Judd–Ofelt theory, and the intensity parameters Ω₂, Ω₄ and Ω₆ are found to be 5.50×10⁻²⁰, 1.96×10⁻²⁰ and 2.34×10⁻²⁰ cm², respectively. The emission cross-section has been calculated by the Fuechtbauer–Ladenbury method. The spectroscopic parameters of Er³⁺:YbVO₄ are compared with other typical laser hosts.     

Crystal growth and spectroscopic properties of erbium doped Lu2SiO5

A high optical quality erbium doped Lu₂SiO₅ single crystal has been grown by the Czochralski method. The distribution coefficient of Er³⁺ was measured to be ∼0.926. The absorption and emission spectra as well as the fluorescence decay curve of the excited state ⁴I_13/2 were measured at room temperature. The spectroscopic parameters were calculated using the Judd–Ofelt theory, and the J–O parameters Ω₂, Ω₄ and Ω₆ were found to be 4.451×10^-20, 1.614×10^-20 and 1.158×10^-20 cm², respectively. The room-temperature fluorescence lifetime of the Er³⁺⁴I_13/2→⁴I_15/2 transition was measured to be 7.74 ms. The absorption and emission cross-section as well as the gain cross-section in the eye-safe regime of 1400–1700 nm were also determined and discussed.     

Reduction of grown-in dislocation density in Ge Czochralski-grown from the B2O3-partially-covered melt

Germanium (Ge) single crystals with an extremely low density of grown-in dislocations were grown by the Czochralski (CZ) technique with boron oxide (B₂O₃) liquid. Because attachment of particles floating on the melt surface to a growing Ge crystal leads to generation of dislocations during the growth, partial covering of the Ge melt surface with B₂O₃ liquid was attempted. Such attachment of particles was drastically suppressed or the particles were caught by the introduction of B₂O₃ liquid, and a particle-free Ge melt was realized in the central region of the melt surface. Ge single crystals were successfully grown from such melt, the grown-in dislocation density being 0–1×10³ cm⁻², which was remarkably lower than that in Ge crystals grown by a conventional CZ technique. The contaminations by B and O atoms of the grown crystal detected by SIMS analysis were very low. These Ge crystals have the potential for application to be applied as high-quality, dislocation-free substrates of GaAs solar cells for various usages including in space.     

Floating-zone growth of large high-quality CoAl2O4 single crystals

We report the first successful floating-zone growth of high-quality CoAl₂O₄ single crystals with volume up to 1 cm³ free from inclusions and sub-grains. The neutron rocking curves of the CoAl₂O₄ crystal have the width of about 0.30 degree proving the excellent quality of the grown samples. X-ray synchrotron experiments show that crystals have spinel structure with the lattice constant a₀=8.09853(1) Å. Magnetization measurements give the effective magnetic moment μ_eff=4.63 μ_B per Co⁺² ion in a good agreement with previous measurements on ceramic samples.     

Spectroscopic properties of Er-doped Na2O-Sb2O3-B2O3-SiO2 glasses

Spectroscopic properties of Er³⁺-doped Na₂O-Sb₂O₃-B₂O₃-SiO₂ glasses have been investigated for developing 1.5-μm broadband fiber amplifiers. An intense 1.5-μm near infrared emission with a broad full width at half maximum (FWHM) of 88 nm has been obtained for Er³⁺-doped 5Na₂O-20Sb₂O₃-35B₂O₃-40SiO₂ glass upon excitation with a 980 nm laser diode. The obtained emission cross-section of the ⁴I_13/2 → ⁴I_15/2 transition and the lifetime of the ⁴I_13/2 level of Er³⁺ ions are 6.8 × 10⁻²¹ cm² and 0.36 ms, respectively. It is noted that the product of the emission cross-section and the FWHM of the glass, σ_e × FWHM, is as great as 598.4 × 10⁻²¹ cm² nm, which is comparable or higher than that of Er³⁺-doped bismuth-based and tellurite-based glasses. These special optical properties encourage in identifying them as important materials for potential applications in high performance optics and optical communication networks.     

Optical properties of and concentration quenching in Bi2O3-B2O3-Ga2O3 glasses

Er₂O₃-doped Bi₂O₃-B₂O₃-Ga₂O₃ glasses were prepared by the conventional melt-quenching method, and the Er³⁺:⁴I_13/2 → ⁴I_15/2 fluorescence properties are studied for different Er³⁺ concentrations. when the Er₂O₃ concentration increases from 0.03 to 3.0 mol%, the measured lifetime of Er³⁺:⁴I_13/2 level decrease from 2.24 to 0.9 m s, and from 0.25 to 0.20 m s for the Er³⁺:⁴I_11/2 level. The fast energy migration among Er³⁺ ions cause the reduction of lifetime of the ⁴I_13/2 level, whereas the change in the ⁴I_11/2 level is mainly due to a cooperative upconversion process (⁴I_11/2, ⁴I_11/2) → (⁴F_7/2, ⁴I_15/2). Based on the dipole-dipole interaction theory, the interaction parameter, C_Er,Er, for the migration rate of Er³⁺:⁴I_13/2 ↔ ⁴I_13/2 was calculated to be 32 × 10⁻⁴⁰ cm⁶ s⁻¹.     

The effect of PbF2 content on the microstructure and upconversion luminescence of Er-doped SiO2-PbF2-PbO glass ceramics

The Er³⁺ doped transparent oxyfluoride glass ceramics were obtained by appropriate heat treatment of the precursor glasses with composition (mol%) 50SiO₂-xPbF₂-(50 − x)PbO-0.5ErF₃. The microstructure and optical properties of the glasses and glass ceramics were determined by differential scanning calorimetry (DSC), X-ray diffraction (XRD), absorption spectra and luminescence spectra. The intensity of upconversion luminescence significantly increased in glass ceramics compared to that in precursor glass. The emission bands centered around 660 nm (⁴F_9/2 → ⁴I_15/2) and 410 nm (²H_9/2 → ⁴I_15/2) were simultaneously observed in glass ceramics but cannot be seen in the corresponding precursor glass. The influence of different PbF₂ content on the microstructure and upconversion luminescence of the samples was analyzed in detail. The results indicated that with the increase of PbF₂ content, the Ω₂ was almost the same and the ratios of red to green upconversion luminescence decreased in glass ceramics.     

Crystal growth and characterization of two-leg spin ladder compounds: Sr14Cu24O41 and Sr2Ca12Cu24O41

Single crystals of Sr_14−xCa_xCu₂₄O₄₁ (x=0 and 12) are grown by the travelling solvent floating zone technique using an image furnace. The grown crystals are characterized for their single crystallinity by the X-ray and Neutron Laue method. The magnetic susceptibility measurements in Sr₁₄Cu₂₄O₄₁ show considerable anisotropy along the main crystallographic axes. Low-temperature specific heat measurement and DC susceptibility measurement in Ca-doped crystal showed antiferromagnetic ordering at 2.8 K at ambient pressure. High-pressure AC susceptibility measurement on Ca-doped crystal showed a sharp superconducting transition at 2 K under 40 kbars. T_c onset reached a maximum value of 9.9 K at 54 kbars. The bulk superconductivity of the sample is confirmed by the high-pressure AC calorimetry with T_c max=9.4 K and T_N=5 K at 56 kbars.     

Thermodynamic mixing properties of liquids in the system Na2O-SiO2

Enthalpies of fusion have been measured by differential scanning calorimetry for a Na₂O-SiO₂ system at 50, 66.6, and 74.4 mol% SiO₂. Enthalpies of mixing of liquids obtained from different calorimetry techniques are critically evaluated. The data on calorimetric enthalpy, activity of Na₂O, cristobalite liquidus, and immiscibility gap are used to determine the enthalpy and entropy of mixing of sodium-silicate liquids are determined as a function of composition by the least squares method. The derived mixing properties are based only on the experimental data and are independent of any assumption about the structure and chemical species in liquids. The enthalpy of mixing has a minimum value of −120 kJ/mol at 35-40 mol% SiO₂ and is convex upward around 80-90 mol% SiO₂. The entropy of mixing have a maximum value of + 6 J/K-mol at 75 mol% SiO₂, and it decreases with the SiO₂ content to −5 J/K-mol at 40 mol% SiO₂. This decrease in entropy can be accounted for by ideal mixing of Q⁴, Q³, and Q^{0 + 1 + 2} (= Q⁰ + Q¹ + Q²) species in the liquids and is responsible for the negative temperature dependence of the partial molar Gibbs energy of mixing of Na₂O, observed in activity measurements. Comparison of the present results with previous values suggests that a quasi-chemical model and the Adam-Gibbs model overestimate the configurational entropy of mixing of liquids.     

Characterization of a newly synthesized organic nonlinear optical crystal: Urea ninhydrin monohydrate

Urea ninhydrin monohydrate (UNM) was synthesized and grown for the first time from aqueous solution employing the slow evaporation method. Single crystal structure was determined by X-ray diffraction data and it reveals that the crystal belongs to centrosymmetric with space group of P2₁/c. The grown crystals were characterized by thermogravimetric analysis (TGA), differential thermal analysis (DTA) and UV–vis–NIR spectroscopy. Preliminary Z-scan measurement indicates that nonlinear refractive index of this crystal is −4.1×10⁻⁸ cm²/W. The etching study was performed to assess the growth pattern of the crystal. Dielectric response of the crystal was analyzed for different frequencies and temperatures.     

Crystal growth and characterization of K2B4O11H8

Single crystals of K₂B₄O₁₁H₈, a non-centrosymmetric borate material, have been prepared by slow evaporation of water solution at room temperature. The crystals were colorless and transparent with smooth faces. The single-crystal X-ray diffraction analysis showed that K₂B₄O₁₁H₈ crystallized in the orthorhombic space group P2₁2₁2₁ with a=6.8556(6) Å, b=11.7787(12) Å, c=12.8949(14) Å, Z=4, R₁=0.0188, and wR₂=0.0464. The powder X-ray diffractometry (PXRD), infrared spectrum, transmittance spectrum, TG–DTA curves and second harmonic generation properties of title compound have been determined.     

Development and characterizations of BaO-CaO-Al2O3-SiO2 glass-ceramic sealants for intermediate temperature solid oxide fuel cell application

Several compositions based on BaO-CaO-Al₂O₃-SiO₂ (BCAS) glass system have been studied in this investigation to see their applicability as sealant for solid oxide fuel cell (SOFC). The glasses as well as the corresponding glass-ceramics have been systematically characterized by differential thermal analysis, dilatometry, X-ray diffractometry, electron microscopy and impedance analysis to examine their suitability as sealant. While the glass transition temperature (T_g) determined from DTA are within 600-665 °C, the coefficient of thermal expansion (CTE) can be tailored between 9.5 and 13.0 × 10⁻⁶ K⁻¹. These glasses are found to be well adhered with metallic interconnects, such as commercial ferritic steel (Crofer22APU), at an optimum sealing temperature of 850 °C. The shrinkage behavior of the developed glasses in their pellet form has also been investigated. The resistivities of the glass-ceramics, as obtained from impedance analysis, are found to be within 10⁴-10⁶ Ω cm at 800 °C. Under sandwiched condition between two metals, some of the developed compositions are found to maintain this high resistivity even after 100 h of operation. One of the glass compositions has shown a low leak-rate of the order of ∼10⁻⁷ Pa m² s⁻¹.     

Preparation of single-crystalline ZnO films on ZnO-buffered a-plane sapphire by chemical bath deposition

High-quality zinc oxide (ZnO) films were successfully grown on ZnO-buffered a-plane sapphire (Al₂O₃ (1 1 2¯ 0)) substrates by controlling temperature for lateral growth using chemical bath deposition (CBD) at a low temperature of 60 °C. X-ray diffraction analysis and transmission electron microscopy micrographs showed that the ZnO films had a single-crystalline wurtzite structure with c-axis orientation. Rocking curves (ω-scans) of the (0 0 0 2) reflections showed a narrow peak with full width at half maximum value of 0.50° for the ZnO film. A reciprocal space map indicated that the lattice parameters of the ZnO film (a=0.3250 nm and c=0.5207 nm) were very close to those of the wurtzite-type ZnO. The ZnO film on the ZnO-buffered Al₂O₃ (1 1 2¯ 0) substrate exhibited n-type conduction, with a carrier concentration of 1.9×10¹⁹ cm⁻³ and high carrier mobility of 22.6 cm² V⁻¹ s⁻¹.     

Structure and growth morphology of Gd2O3-doped CeO2 thin films

Gd₂O₃-doped CeO₂ (Gd_0.1Ce_0.9O_1.95, GDC) thin films were synthesized on (1 0 0) Si single crystal substrates by a reactive radio frequency magnetron sputtering technique. Structures and surface morphologies were characterized by X-ray diffraction (XRD), Atomic Force Microscopy (AFM) and one-dimensional power spectral density (1DPSD) analysis. The XRD patterns indicated that, in the temperature range of 200–700 °C, f.c.c. structured GDC thin films were formed with growth orientations varying with temperature—random growth at 200 °C, (2 2 0) textures at 300–600 °C and (1 1 1) texture at 700 °C. GDC film synthesized at 200 °C had the smoothest surface with roughness of R_rms=0.973 nm. Its 1DPSD plot was characterized with a constant part at the low frequencies and a part at the high frequencies that could be fitted by the f^−2.4 power law decay. Such surface feature and scaling behavior were probably caused by the high deposition rate and random growth in the GDC film at this temperature. At higher temperatures (300–700 °C), however, an intermediate frequency slope (−γ₂≈−2) appeared in the 1DPSD plots between the low frequency constant part and the high frequency part fitted by f⁻⁴ power law decay, which indicated a roughing mechanism dominated by crystallographic orientation growth that caused much rougher surfaces in GDC films (R_rms>4 nm).     

Crystallization behavior and microstructure of powdered and bulk ZnO-Al2O3-SiO2 glass-ceramics

The crystallization behavior of glass with the composition: 55.6 mol% SiO₂, 22.8 mol% Al₂O₃, 17.7 mol% ZnO and 3.84 mol% of TiO₂ as nucleating agent and with different particle sizes has been studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and tranmission electron microscopy (TEM). In glass powders two crystalline phases: zinc-aluminosilicate s.s. with high-quartz structure, Zn_x/2Al_xSi_3−xO₆, (x varies dependent on heat-treatment temperature) and gahnite are formed. The ratio of these phases depends on particle sizes. In bulk glass, however, gahnite is the sole crystalline phase. The composition of initially formed zinc-aluminosilicate s.s. was determined by Rietveld refinement of XRD patterns to be Zn_0.69Al_1.38Si_1.62O₆. With temperature increase, the amount of zinc-aluminosilicate s.s decreased with simultaneous reduce of zinc and aluminum incorporated in the structure. Eventually at 1423 K almost pure high-quartz structure was formed. The activation energies of zinc-aluminosilicate s.s. and gahnite crystallization were determined by non-isothermal method to be 510 ± 18 and 344 ± 17 kJ mol⁻¹, respectively. The latter value matches well with those cited in literature for crystal growth of gahnite in similar glasses. That is attributed to the fact that the high-quartz structure acts as a precursor for gahnite crystallization.     

Redox freezing temperature and Bartenev equation in a 25Na2O-15B2O3-60SiO2 glass doped with chromium and manganese

In a melt with the base mol% composition 25Na₂O-15B₂O₃-60SiO₂, doped with chromium and manganese, a redox reaction takes place during cooling the melt. This reaction was studied using high temperature UV-vis spectroscopy. Above 600 °C, the reaction is in equilibrium and shifted during cooling to the Cr³⁺ and Mn³⁺ species. At temperatures between 500 and 600 °C, the kinetics of the redox reaction is decisive and the cooling rate plays an important part. At temperatures < 500 °C, the reaction is frozen in. The smaller the cooling rate, the smaller is the Cr⁶⁺ concentration and the lower is the fictive redox temperature.The kinetics of the reaction was described by a differential equation assuming Arrhenian behaviour. The equation was numerically solved and fictive temperatures were calculated. These temperatures depended on cooling rate similar to Bartenev equation. Activation energies calculated hereof were around 38 kJ?mol⁻¹ larger than those inserted into the kinetic equation. The experimentally determined activation energy is 565 kJ?mol⁻¹, a value much larger than the activation energies of diffusion of the polyvalent elements. The rate determining step in the case of the Cr³⁺/Cr⁶⁺/Mn²⁺/Mn³⁺ system is the electron transfer reaction, because a notable structural rearrangement is necessary during the course of the electron transfer reaction (Cr³⁺ and Cr⁶⁺ occur in octahedral and tetrahedral coordination, respectively). The latter leads to a large inner reorganisation energy and to an activation energy similar to that of the viscous flow. In the case of the redox reaction between copper and arsenic, the activation energy is much smaller (210 kJ?mol⁻¹), because here the coordination numbers do not change during the course of the redox reaction.