Liquid phase epitaxy of films with langasite structure

Epitaxial films of Na₂CaGe₆O₁₄ with langasite structure were deposited by liquid phase epitaxy (LPE) technique on isomorphic Nd₃Ga₅SiO₁₄ substrates at a growth temperature of about 1000°C using K₂O–V₂O₅ based flux. The films were about 100 μm in thickness and had rough surface morphology. The film composition measurements were made by scanning electron-probe microanalysis (EPMA). EPMA data indicated low content of flux forming K⁺ and V⁵⁺ cations in the films grown. Ca²⁺ enrichment and Na⁺ decrease were detected in the vicinity of film/substrate interfaces.     

Er doped waveguide amplifiers written with femtosecond laser in germanate glasses

The authors report the fabrication and characterization of active waveguides in GeO₂–PbO–Ga₂O₃ glass samples doped with Er³⁺, written with a femtosecond laser delivering pulses of 150 fs duration at 1 kHz repetition rate. Permanent refractive index change was obtained and waveguides were formed under different laser pulse energies and scan velocities. The passive and active optical properties of the waveguides were investigated. The minimum value of propagation loss was of 4.8 dB/cm. Optical amplification at 1.5 μm under 980 nm excitation was observed showing a maximal internal gain of 2.7 dB/cm.     

A low-temperature reactive sintering process for the 5Li2O–1Nb2O5–5TiO2 microwave dielectric ceramics

The B₂O₃-doped 5Li₂O–1Nb₂O₅–5TiO₂ composite microwave dielectric ceramics prepared by conventional and low-temperature single-step reactive sintering processes were investigated in the study. Without any calcinations involved, the Nb₂O₅ mixture of Li₂CO₃ and TiO₂ was pressed and sintered directly in the reactive sintering process. More uniform and finer grains could be obtained in the 5Li₂O–1Nb₂O₅–5TiO₂ ceramics by reactive sintering process, which could effectively save energy and manufacturing cost. And relatively good microwave dielectric properties of _r = 41, Q × f = 9885 GHz and τ_f = 43.6 ppm/°C could be obtained for the 1 wt.% B₂O₃-doped ceramics reactively sintered at 900 °C.     

Effect of Ce(Eu) codoping on the spectroscopic properties of Er in bismuth-germanate glass

In order to improve the transition rate from the ⁴I_11/2 level to the 1.53 μm fluorescence emitting ⁴I_13/2 level of Er³⁺, the Ce³⁺ and Eu³⁺ ions were respectively introduced into the Er³⁺ doped bismuth-germanate glass with a composition of Bi₂O₃–GeO₂–Ga₂O₃–Na₂O. The energy transfer mechanisms between Er³⁺ and the codopants were discussed based on their energy level diagrams. Though Ce³⁺ was less effective than Eu³⁺ on the decrease of the ⁴I_11/2 level lifetime, it hardly influenced the lifetime value of ⁴I_13/2 level. Both the ⁴I_11/2 and ⁴I_13/2 levels were depleted severely at the same time with the codoping of Eu³⁺. As a result, Er³⁺/Ce³⁺ codoping improved the 1.53 μm fluorescence emission intensity, while Er³⁺/Eu³⁺ codoping had a deleterious effect on it. The results indicate that the Er³⁺/Ce³⁺ is a preferable codoped scheme for bismuth-germanate glass with low phonon energy to obtain an efficient broadband EDFA pumped at 980 nm.     

Experimental researches on characteristics of vapor–liquid equilibrium of NH3–H2O–LiBr system

An improved system of NH₃–H₂O–LiBr was proposed for overcoming the drawback of NH₃–H₂O absorption refrigeration system. The LiBr was added to NH₃–H₂O system anticipating a decrease in the content of water in the NH₃–H₂O–LiBr system. An equilibrium cell was used to measure thermal property of the ternary NH₃–H₂O–LiBr mixtures. The pressure–temperature data for their vapor–liquid equilibrium (VLE) data were measured at ten temperature points between 15–85 °C, and pressures up to 2 MPa. The LiBr concentration of the solution was chosen in the range of 5–60% of mass ratio of LiBr in pure water. The VLE for the NH₃–H₂O–LiBr ternary solution was measured statically. The experimental results show that the equilibrium pressures reduced by 30–50%, and the amount of component of water in the gas phase reduced greatly to 2.5% at T=70 °C. The experimental results predicted much better characteristics of the new ternary system than the NH₃–H₂O system for the applications.     

Characterization of SiO2–Na2O–Fe2O 3–CaO–P2O 5–B 2O 3 glass ceramics

Bioactivity and magnetic properties were investigated in glass and glass ceramics based on the SiO₂–Na₂O–Fe₂O₃–CaO–P₂O₅–B₂O₃ system to find their suitability as thermoseed for hyperthermia treatment of cancer. The effect of change in compositions on bioactivity was examined in simulated body fluids. The glass ceramic samples exhibit Na₃CaSi₃O₈ and Na_3-XFe_XPO₄ phases. After dipping the glass ceramic samples in simulated body fluids silica hydrogel first forms, followed by an amorphous calcium phosphate layer. Magnetic and microwave resonance experiments further demonstrate the potential of these glass ceramics for possible use in hyperthermia.     

Phase Relations in the Na2O–Al2O3–Nb2O5and CaO–Al2O3–Nb2O5Systems

Phase relations in the Na₂O–Al₂O₃–Nb₂O₅and CaO–Al₂O₃–Nb₂O₅systems were studied. The Na₂O system was found to contain neither ternary compounds nor niobate–aluminate solid solutions. In the CaO system, a ternary compound of composition 4CaO · Al₂O₃·Nb₂O₅was identified (cubic structure, a= 7.628 Å, Z= 2, _meas= _x= 4.43 g/cm³).     

Optical properties and structure of R2O–Ga2O3–SiO2 and RO–Ga2O3–SiO2 glasses

Refractive index and molar refraction of Li₂O–, Na₂O–, CaO–, and BaO–Ga₂O₃–SiO₂ glasses have been used to test the validity of a structural model of silicate glasses containing Ga₂O₃ glasses. Ga₂O₃ enters these types of glass in a similar manner as Al₂O₃. It is assumed that, for (SiO₂/Ga₂O₃) >1 and (Ga₂O₃/R₂O) ≤1, Ga₂O₃ associates primarily with modifier oxides to form GaO₄ units. The rest of modifier oxide forms silicate units with non-bridging oxygen ions. Silicate structural units have the same factors as found for binary alkali- and alkaline earth silicate glasses. Differences between experimental and model values suggest another structure for (Ga₂O₃/SiO₂) ≥1.     

Correlation of electrical properties and internal friction in mixed conduction glasses containing ionic and electronic conduction (1) Fe2O3-Na2O-P2O5 glasses

The electrical properties and internal friction in (40–x)Fe₂O₃·xNa₂0.60P₂O₅ glasses were measured. Two or three peak on internal friction were observed in the temperature range of –100 to 300° C at a frequency of about 1 Hz. The peak area of internal friction could be explained quantitatively by the additivity law of diffusion of Na⁺ ion and hopping of electrons which are carriers similar to those of dielectric loss. Activation energy, peak temperature of dielectric loss and internal friction showed almost the same value. Both relaxation phenomena have the same mechanism which is due to the diffusion of Na⁺ion and the hopping of electrons between Fe²⁺ Fe³⁺. The high-temperature peak is assumed to result from the interaction between protons or alkali ions and non-bridging oxygen.     

Synthesis of Fe-substituted Al-mordenites by hydrothermal method

Al-mordenite and Fe-mordenite were synthesized with the tetraethylammonium as atemplate by hydrothermal method at 150°C in the Na₂O–Al₂O₃–SiO₂–H₂O and Na₂O–Fe₂O₃–SiO₂–H₂O system, respectively. Synthesis of several Al-mordenites substituted with Fe, Al/Fe ratio = 75/25, 50/50, 25/75, were also attempted in the Na₂O–Al₂O₃–Fe₂O₃–SiO₂–H₂O system under the same conditions by the hydrothermal method. The continuous solid solution of Fe in Al-mordenite was successfully obtained in mordenites with various Al-Fe molar ratios. Al-mordenite crystal was tablet-like with approximately 20–30 m in diameter and 5–10 m in thickness. Fiber-like Fe-mordenite grew up to 20–30 m in length and 5 m in diameter. The morphology of Fe-substituted Al-mordenite was cubic-like with 5–10 m in size. The size of Fe-substituted Al-mordenite decreased with the increase of Fe-content.     

Effective removal and fixation of Cr(VI) from aqueous solution with Friedel's salt

Friedel's salt (3CaO·Al₂O₃·CaCl₂·10H₂O or Ca₄Al₂(OH)₁₂Cl₂(H₂O)₄) is a calcium aluminate hydrate formed by hydrating cement or concrete in seawater at a low cost. In the current study, we carefully examined the adsorption behaviors of Friedel's salt for Cr(VI) from aqueous solution at different concentrations and various initial pHs. The adsorption kinetic data are well fitted with the pseudo-first-order Lageren equation at the initial Cr(VI) concentration from 0.10 to 8.00 mM. Both the experimental and modeled data indicate that Friedel's salt can adsorb a large amount of Cr(VI) (up to 1.4 mmol Cr(VI)/g) very quickly (t_1/2 = 2–3 min) with a very high efficiency (>99% Cr(VI) removal at [Cr] < 4.00 mM with 4.00 g/L of adsorbent) in the pH range of 4–10. In particular, the competitive adsorption tests show that the Cr(VI) removal efficiency is only slightly affected by the co-existence of Cl⁻ and HCO₃⁻. The Cr(VI)-fixation stability tests show that only less than 0.2% adsorbed Cr(VI) is leaching out in water at pH 4–10 for 24 h because the adsorption/exchange of Cr(VI) with Friedel's salt leads to the formation of a new stable phase (3CaO·Al₂O₃·CaCrO₄·10H₂O). This research thus suggests that Friedel's salt is a potential cost-effective adsorbent for Cr(VI) removal in wastewater treatment.     

Synthesis and Characterization of Potassium Gallate Silicate with the Zeolite LStructure

A Ga analog of zeolite L(Ga-L–D) with a high degree of crystallinity was synthesized in the K₂O–Ga₂O₃–SiO₂–H₂O system and was characterized by x-ray diffraction, x-ray spectrochemical analysis, and thermal analysis. The results were used to assess the crystallization kinetics of Ga-L–D.     

Creep rupture studies of two alumina-based ceramic fibres

Creep rupture tests were performed in air on two polycrystalline oxide fibres (Al₂O₃, Al₂O₃-ZrO₂) using both filament bundles and single filaments. Tests were performed at applied stresses ranging from 50–150 MPa over the temperature range 1150–1250 °C. Under these conditions, creep rates for the alumina-zirconia fibre ranged from 4.12 × 10^–8–7.70 × 10^–6s^–1. At a given applied stress, at 1200°C, creep rates for the alumina fibre were 2–10 times greater than those of the alumina-zirconia fibre. Stress exponents for both fibres ranged from 1.2–2.8, while the apparent activation energy for creep of bundles of the alumina-zirconia fibre was determined to be 648 ± 100kJmol^–1. For the alumina-zirconia fibre, the two test methods yielded similar steady-state creep rates, but the rupture times were generally found to be longer for bundles than for single filaments. The steady-state creep behaviour of these alumina-based fibres is consistent with an interface-reaction-controlled diffusion-controlling mechanism.     

Preparation of TeO2 based thin films by nonhydrolytic sol–gel process

To solve the problem of the extremely high hydrolytic reactivity of tellurium alkoxides in hydrolytic sol–gel method, the nonhydrolytic sol–gel process has been applied as a novel route for producing TeO₂ based thin films. The transition of nonhydrolytic sol–gel was monitored by means of ¹H NMR, FT-IR and Raman techniques. These results show that the formation of Te–O–Te bonds in gel networks mainly resulted from the nonhydrolytic cross-condensation reaction between different Te–OR groups. The decomposition process and structure evolution of the nonhydrolytic gel products were investigated and managed. Results from DTA and XRD analyses show that metallic tellurium, β-TeO₂ and α-TeO₂ phase appeared in the film during heat-treatment process at around 300, 350 and 400 °C, respectively. The formation of metallic tellurium can be alleviated through preheating the gel films under O₂ atmosphere or by additions of the second component. Crystallization of α-TeO₂ could be retarded by additions of TiO₂ or Al₂O₃, and the transparent, homogeneous amorphous TeO₂ based thin films were obtained by the methods above. The nonhydrolytic sol–gel process developed in this study offers a simple and practical method for fabricating TeO₂ based thin film devices.     

Properties and structure of germanium-containing lithium aluminoborate glasses

Glasses of the system Li₂O–Al₂O₃–GeO₂–B₂O₃ have been investigated. The effect of replacement of the B₂O₃ by GeO₂ on the physicochemical properties of the glasses has been studied. The density and the refractive index were found to increase as the GeO₂:B₂O₃ ratio (r) increases. In contrast, the molar volume was found to decrease as r increases. Dilatometric measurements showed that the thermal expansion coefficient () increases with the increase of r whereas both of the glass transition temperature (T_g) and the softening point (T_s) decreases with increasing r. Fourier transform infrared (FTIR) spectroscopy revealed that BO₃ structural units increase at the expense of BO₄ units as r increases. It is indicated also that GeO₆ units are the preferred germanium structural units that participate into the glass network. The electrical conductivity was found to decrease with increasing r. This was attributed to the large difference between the two atoms (Ge and B), which increases the stability and therefore decreases the conductivity of the investigated glasses. The conductivity results were correlated with those from the FTIR study.     

Preparation and characterization of sol–gel derived glasses in the ternary Na2O–Al2O3–P2O5 system

A new sol–gel synthesis route to organic free Na₂O–Al₂O₃–P₂O₅ xerogels was developed. These xerogels contain P₂O₅ up to 67.5 mole % and Al₂O₃ up to 20 mole % and could be melted to homogeneous glasses in air at significantly lower temperatures than those applied using the conventionally melting method. Aluminum isopropoxide dissolved in isopropanol, orthophosphoric acid dissolved in isopropanol and sodium nitrate were used as precursors for Al₂O₃, P₂O₅ and Na₂O respectively. Clear stable alcoholic solutions were prepared in the presence of HNO₃. Addition of HNO₃ in the concentration used, enabled homogeneous mixing of the precursors, controlled over the gelation step and prevented the fast precipitation of the AlPO₄ crystalline phase which breaks down the glass formation ability. The sol–gel route developed was investigated using different analytical tools. Differential thermal analysis (DTA) coupled with thermo-gravimetric (TG) analysis indicated that neither organic residues nor sodium nitrate residues were present in the dried gels after gelation. Fourier transform infrared spectroscopy (FTIR) showed the presence of all characteristic phosphate groups and bonds in the dried gels, especially the P=O and the P–O–P bonds. Solid state ³¹P Magic angle spinning nuclear magnetic resonance (MAS NMR) revealed the formation of Q² chain-like polyphosphates of variable polymerization degrees in the dried gels. Solid state ²⁷Al MAS NMR revealed that octahedrally coordinated Al is the preferred moiety in the dried gels. However, powder X-ray diffraction (XRD) investigation indicated the presence of crystalline Q¹ oligomeric pyrophosphate species in the dried gels. Isotropic chemical shifts belonging to these pyrophosphate species were also recorded in the ³¹P MAS NMR spectra. Characterization of the prepared glasses showed that their properties are in very good agreement with those glasses prepared by the conventionally melting method.     

Assessment of the thermal stability of anodic alumina membranes at high temperatures

The thermal stability of anodic alumina membranes (AAMs) annealed in air from 750 °C up to 1100 °C was investigated. AAMs were produced by single-step anodising of laminated AA1050 in 0.30 M oxalic acid medium. The barrier layer provided thermal stability to the membranes, since it avoided or minimized bending and cracking phenomena. X-ray diffraction (XRD) analyses revealed that as-synthesized AAMs were amorphous and converted to polycrystalline after heat-treating above 750 °C. However, porous and barrier layers did not re-crystallize in the same way. The porous layer mainly crystallized in the γ-Al₂O₃ phase within the range of 900–1100 °C, while the barrier layer was converted to the α-Al₂O₃ phase at 1100 °C. Different grain sizes were also estimated from Scherrer's formula. Scanning electron microscopy (SEM) images pointed out that cell wall dilation of the porous layer explained membrane cracking, which was avoided in presence of the barrier layer.     

Compositional dependence of spectroscopic parameters of Dy ions in Ge–Ga–Se glasses

Dy³⁺ doped chalcogenide glasses from Ge–Ga–Se system were prepared and spectroscopic parameters of Dy³⁺ ions in these glasses were studied on the basis of Judd–Ofelt theory. We have found that the values of Judd–Ofelt intensity parameters Ω_t (t = 2, 4, 6) have maximal values at the GeSe₂–Ga₂Se₃ tie-line. Largest values of spectroscopic parameters of 1.3 µm Dy³⁺ transition (⁶F_11/2, ⁶H_9/2 → ⁶H_15/2), localized again at the GeSe₂–Ga₂Se₃ tie-line, confirm the importance of the stoichiometry of amorphous matrix for optical properties of doping rare-earth ions.     

Phase equilibria in the system Na2O-B2O3-Ga2O3 at 600°C

Phase equilibria in the system Na₂O-B₂O₃-Ga₂O₃ were investigated at 600°C using quenching and X-ray powder techniques. Many, but not all the binary phases reported previously were confirmed, no new binary phases were found. The ternary phase diagram was solved and a new phase, 3Na₂O·4B₂O₃·Ga₂O₃, discovered. The X-ray powder data are given for this and also for -Ga₂O₃ and Na₂O·Ga₂O₃. Solid solution effects were investigated for the primary and binary phases by comparison of patterns; no solid solution effects were detected. These results are compared with those of investigations of two pseudo-binaries reported previously, both of which reported other ternary phases which could not be confirmed. Although there is some conflict between the results, it is pointed out that the validity of one pseudo-binary is doubtful due to chemical analysis of one ternary phase, while the report on the other pseudo-binary gives an X-ray powder pattern of a ternary phase which is probably impure.     

Second harmonic generation in surface crystallized 30GeS2 · 35Ga2S3 · 35AgCl chalcohalide glasses

The infrared transmitting surface crystallized chalcohalide glasses containing nontoxic and excellent nonlinear optical AgGaGeS₄ crystallites were fabricated by heat-treatment of the as-prepared 30GeS₂ · 35Ga₂S₃ · 35AgCl chalcohalide glass at 350 °C (T_g −10 °C) for 24 h. An intensive second harmonic generation (SHG) was observed clearly using the Maker fringe technique, and the origin of SHG was mainly ascribed to the AgGaGeS4 nonlinear optical crystallites contained in the surface crystallized layer. The thickness of the surface crystallized layer showing SHG activation is approximate 50 μm. The χ⁽²⁾ susceptibility of the prepared surface crystallized 30GeS₂ · 35Ga₂S₃ · 35AgCl chalcohalide glass is calculated to be about 12.4 pm/V at a fundamental wavelength of 1064 nm, which indicates a promising nonlinear optical material in the infrared spectral region.