Colloidal particles with various glass transition temperatures: preparation, assembly, and the properties of stop bands under heat treatment

Monodisperse P(St-co-nBA-co-AA) colloidal microspheres with various glass transition temperatures (T _gs), whose average particle sizes were about 300 nm, were prepared using soap-free emulsion polymerization by adjusting the ratio of styrene and n-butyl acrylate. Colloidal photonic crystals were assembled with these microspheres by vertical deposition method. Stop bands of colloidal crystals under different temperatures have been characterized. The relationship between the stop band and temperature was indicated. The microstructure and reflectance spectra of photonic crystals were characterized by SEM and fiber spectrometer, respectively. Results showed that as the temperature increased, only a little red shift of stop band appeared in the vicinity of T _g and the intensity of the maximum reflection peak decreased until the stop bands disappeared. Furthermore, enough heating time at the T _g ±2 °C could also lead to the disappearance of stop bands. What’s more, colloidal crystal films with certain connection strength were obtained by simple heating.     

Tl1−xIn1−xSnxSe2 (x = 0, 0.1, 0.2, 0.25) single-crystalline alloys as promising non-linear optical materials

Novel materials for the infrared two-photon absorption—Tl_1?xIn_1?xSn_xSe₂ single crystals (x = 0, 0.1, 0.2, 0.25) were grown. Their optoelectronic properties including two-photon absorption at wavelength equal to 9.4 μm at different temperatures were studied. From the spectral data it was established that band gap energy increases with increasing SnSe₂ content in the solid solutions reaching its maximum for the largest content (x = 0.25). The infrared two photon absorption has achieved its maximal value at x = 0.1. The temperature dependence of the optical band gap at various compositions in the range of 77–300 К is practically linear. The band gap value decreases with the increase of T causing the spectral shift of the absorption edge to the low-energy region. Additionally X-ray photoelectron core-level spectra for pristine and Ar⁺-ion irradiated surfaces of Tl_1?xIn_1?xSn_xSe₂ single crystals have been measured.     

Synthesis, IR, crystallization and dielectric study of (Pb, Sr)TiO 3 borosilicate glass–ceramics

Eleven glass compositions were prepared by melt and quench method with progressive substitution of SrO for PbO (0?≤?x?≤ 1·0) with a step-wise increment of 0·10 in the glass [(Pb _x Sr_1???x )OTiO₂]–[(2SiO₂B₂O₃)]–[BaO·K₂O]·Nb₂O₅ (mol percentage) system. The infrared spectra (IR) of various glass compositions in the above mentioned glass system was recorded over a continuous spectral range 400–4000 cm^???1 to study their different oxides structure systematically. Differential thermal analysis (DTA) was recorded from room temperature (~27 °C) to 1400 °C employing a heating rate of 10 °C /min to determine glass transition temperature, T _g and crystallization temperature, T _c. The melting temperature, T _m, of these glass compositions was found to be in the range 597–1060 °C depending on the composition under normal atmospheric conditions. T _g and T _m of glasses were found to increase with increasing SrO content. X-ray diffraction analysis of these glass–ceramic samples shows that major crystalline phase of the glass–ceramic sample with x ≤ 0·5 was found to have cubic structure similar to SrTiO₃ ceramic. Scanning electron microscopy has been carried out to see the surface morphology of the crystallites dispersed in the glassy matrix.     

Synthesis of magnetite nanoparticles by thermal decomposition of ferrous oxalate dihydrate

Two different polymorphs of ferrous oxalate dihydrate were synthesized by precipitation of ferrous ions with oxalic acid: α-Fe(C₂O₄) · 2H₂O with a monoclinic unit cell is obtained after precipitation and ageing at 90 °C, whereas the orthorhombic β-type is formed after precipitation at room temperature. The morphology of the oxalate crystals can be tailored from prismatic crystals of the α-polymorph over star-like aggregates of α/β-mixtures to non-agglomerated crystallites of β-oxalate. Thermal decomposition in air gives hematite at T ≥ 250 °C; if the thermolysis reaction is performed at low oxygen partial pressures (e.g., T = 500 °C and p _O2 = 10^?25 atm) magnetite is obtained. The synthesized magnetite is stoichiometric as signaled by lattice parameters of a ₀ = 8.39 Å. The thermal decomposition of ferrous oxalate is monitored by thermal analysis, XRD, and IR-spectroscopy. The morphology of the oxalate crystals is preserved during thermal decomposition; the oxalates are transformed into spinel particle aggregates of similar size and shape. The crystallite size of the magnetite particles increases with temperature and is 40 or 55 nm, if synthesized from β-oxalate at 500 °C or 700 °C, respectively. The saturation magnetization of the magnetite particles decreases with decreasing particle size. Since the particles are larger than the critical diameter for superparamagnetic behavior they display hysteresis behavior at room temperature.     

Effects of BaNb2O6 addition on microstructure and dielectric properties of BaTiO3 ceramics

(1 ? x)BaTiO₃–xBaNb₂O₆ [(1 ? x)BT–xBN] ceramics with x = 0, 0.005, 0.008, 0.01, 0.02, 0.03 were prepared by a conventional solid-state reaction route. The effect of BN addition on phase composition, microstructure and dielectric properties of BT-based ceramics were investigated by X-ray diffraction, scanning electron microscope and impedance spectroscopy. The results showed that a systematic structure change from the ferroelectric tetragonal phase to pseudo-cubic phase was observed near x = 0.01 at room temperature. It resulted in a considerable change of density, grain size and dielectric properties of the samples when BN was introduced. Meanwhile, it also lowered the sintering temperature of the ceramics. The dielectric constant peak and the variation rate of capacitance at Curie temperature are markedly depressed and broaden with increasing BN content. Especially, the ceramics with x = 0.008 and x = 0.01 showed good dielectric properties over the measured temperature range. Optimal dielectric properties of ε = 3,851, tanδ = 0.7 % at room temperature and Δε/ε₂₅ ≤ ±6.8 % (?55 to 125 °C) were obtained for the BT-based ceramics doped with 0.8 mol% BN, which was obviously superior to BaTiO₃ and BaNb₂O₆ ceramic, and it met the requirements of EIA X7R specifications.     

Synthesis and electroluminescent property of bis (2-(benzimidazol-2-yl) quinolinato) zinc

An emission material, (2-(benzimidazol-2-yl) quinolinato) zinc (ZnBIQ) used for organic light emitting devices, has been synthesized. The melting transition (T_m) of ZnBIQ is 436 °C and no glass transition temperature (T_g) was observed up to 430 °C. The emission spectrum of organic emitting device using ZnBIQ as emitted layer exhibits a broad maximum at 625 nm. The color of the emitted light is in the red region in the CIE coordinate of x=0.54, y=0.39.     

Study of Thermal Behavior and Single Crystal Growth of A 0.8Fe1.81Se2 (A=K, Rb, and Cs)

We have investigated the melting behavior of alkaline iron selenide compounds of composition A _0.80Fe_1.81Se₂ (A=K, Rb, and Cs) by thermogravimetry/differential thermal analysis (TG/DTA). The analysis indicated that all of the compounds melt incongruently and complete melting occurs at 902, 927, and 900 ^°C for A=K, Rb, and Cs, respectively, as confirmed by high temperature optical microscopy (HTOM). Study of DTA shows the structure of the phase separation present in the compounds and both endothermic and exothermic peaks on heating/cooling measurements are clearly observed. The optimum crystallization temperature range is indicated by the significant exothermic peeks on cooling DTA. Large and high quality single crystals can be obtained at a slow cooling/growth rate by the modified Bridgman, flux, or floating zone methods. XRD reflections in the (00l) plane show that all the single crystals represent an intergrowth of two sets of the c-axis characterized by slightly different lattice constants. Magnetization measurements show that the superconducting transition temperature occurs at T _c=31.6 K with shielding fraction volume of ～100 % for K_0.80Fe_1.81Se₂.     

Optical and Magnetic Properties of Ten-Period InGaMnAs/GaAs Quantum Wells

Ten layers of InGaMnAs/GaAs multiquantum wells (MQWs) structure were grown on high resistivity (100) p-type GaAs substrates by molecular beam epitaxy (MBE). A presence of the ferromagnetic structure was confirmed in the InGaMnAs/GaAs MQWs structure, and have ferromagnetic ordering with a Curie temperature, T _C=50 K. It is likely that the ferromagnetic exchange coupling of the sample with T _C=50 K is hole-mediated resulting in Mn substituting In or Ga sites. PL emission spectra of the InGaMnAs MQWs sample grown at a temperature of 170 °C show that an activation energy of the Mn ion on the first quantum confinement level in InGaAs QW is 32 meV and impurity Mn is partly ionized. The fact that the activation energy of 32 meV of Mn ion in the QW is lower than an activation energy of 110 meV for a substitutional Mn impurity in GaAs, indicating an impurity band existing in the bandgap due to substitutional Mn ions.     

Effect of the adding of rod-like attapulgite upon the properties of polyimides produced by random copolycondensation

A series of polyimides (PIs) and polyimide/attapulgite (AT) composite films was successfully prepared by random copolycondensation. The polyimides were synthesized based on 4,4′-diaminodiphenyl ether, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), and 4,4′-oxydiphthalic anhydride (ODPA). By adjusting the ratio of BPADA and ODPA, three different types of anhydride group-terminated PIs were obtained. AT was functionalized by chemical modification with γ-aminopropyltriethoxysilane and then chemical bonded with PI via reaction between amino group and anhydride group, resulting in stable PI/AT composites. The structure and properties of PIs and PI/AT composites were characterized by FTIR, XRD, TG, SEM, DSC, DMA, mechanical measure, and so on. Comparison was given between PIs and PI/AT composites. Results showed that all PIs had good thermal stability and mechanical properties with glass translation temperature (T _g) over 210 °C, 5 % weight loss temperature (T _d,5%) over 494 °C and tension strength of 84–89.9 MPa, breaking elongation around 7 %. More stable, flexible, and much stronger films were obtained after adding 5 wt% AT, which showed 535–548.5 °C, 85.8–118.9 MPa, and 10.3–24.7 % in T _d,5%, tension strength, and breaking elongation, respectively. Much interestingly, we found that AT had the greatest effect on PI-2, the yielding of which occurred during mechanical measure, and PI/AT-2 composite displayed excellent comprehensive properties.     

Effect of the Pb–Te–B–O system glass frits in the front contact paste on the conversion efficiency of crystalline silicon solar cells

In the present paper, many monocrystal silicon (Si) solar cells are produced by screen printing a front contact paste prepared with crystalline silver particles, a series of glass frits with the different lead oxide (PbO) contents in Pb–Te–B–O system glass, and an organic medium. Under scanning electron microscopy, the selective etching of cells screen-printed by pastes containing the glass frits of different PbO contents from low to high (37.2–52.5 mol%) reveals the corrosion degree of antireflection coating and the growth of silver crystallite microstructures on Si substrate. When the PbO content is 42.7 mol% in glass frits, the silver crystallites of optimal size were formed to make the conversion efficiency of cells best. By comparing the cross-section microstructures of solar cells, the different transition temperatures (T_g = 283–546 °C) of glass frits are found to have a substantial impact on wetting behavior during the firing cycle. When the glass T_g is medium (T_g = 393 °C), the optimal glass layer will be obtained to derive photoelectrons smoothly.     

CMR and related properties of single crystals of cation-deficient LaMnO3

Single crystals of LaMnO₃, La_1−xMnO₃ (x=0, 0.04, 0.1) and LaMn_1−xO₃ (x=0.1) have been grown by the floating-zone melting technique. Electrical and magnetic properties of these crystals have been examined. Only La_0.9MnO₃ crystals exhibit ferromagnetism, (T_c∼250 K), an insulator–metal transition around 250 K and CMR (58% at T_c).     

Tin fluorophosphate nonwovens by melt state centrifugal Forcespinning

This report describes the direct melt processing of inorganic tin fluorophosphate (TFP) glass fibers with average diameters ranging from 2 to 4 µm via centrifugal Forcespinning. This was accomplished by using a TFP glass with low glass transition temperature (T _g) and the melt processing capability of Forcespinning. The thermal behavior of TFP glass fibers was investigated by differential scanning calorimetry and thermogravimetric analysis, while the compositional evolution of the fibers was studied using energy-dispersive spectrometry and Fourier-transform infrared spectroscopy. These fibers exhibited excellent thermal stability after thermal post-treatment at 300 °C. The T _g of the thermally treated fibers increased by 100 °C compared to the bulk material. The fibers were found to undergo dehydration and loss of fluorine during thermal treatment, resulting in a rigid and crosslinked glass network with enhanced thermal stability and increased T _g. The enhanced thermal stability demonstrated the potential of TFP fibers for high temperature catalysis and chemical filtration applications.     

Transport Properties of a Single Crystal of Pressure-Induced Superconductor CePtSi2

We synthesized single crystals of pressure-induced superconductor CePtSi₂ by an In-flux method, and measured its electrical resistivity ρ under hydrostatic pressure. At ambient pressure, ρ shows two maxima at T ₁=3.7 K and T ₂=33 K, and a downward bend at the Néel temperature T _N. With increasing pressure T _N decreases and disappears above 1.11 GPa, as reported in a polycrystalline sample. On the other hand, the maximum at T ₁ becomes a shoulder above P _v=1.21 GPa, and begins to increase with increasing pressure, indicating the beginning of a valence crossover.     

Structure,ferroelectric and piezoelectric properties of Bi0.5(Na0.8K0.2)0.5TiO3 modified BiFeO3–BaTiO3 lead-free piezoelectric ceramics

A new lead-free solid solution of (0.75 ? x)BiFeO₃–0.25BaTiO₃–xBi_0.5(Na_0.8K_0.2)_0.5TiO₃ + 1 mol% MnO₂ has been prepared by a conventional ceramic technique and the effects of Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ and sintering temperature on the structure, ferroelectric and piezoelectric properties of the material have been studied. The ceramics sintered at 960 °C for 2 h possess a pure perovskite structure and no second phases can be detected. After the addition of Bi_0.5(Na_0.8K_0.2)_0.5TiO₃, a morphotropic phase boundary of rhombohedral and orthorhombic phases is formed at x = 0.01. The addition of a small amount of Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ can promote the grain growth, while excess Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ causes an inhibition of grain growth. Sintering temperature has an important influence on the structure and electrical properties of the ceramics. The sintering temperature of 960 °C is a critical temperature to obtain the ceramics with good piezoelectric properties. For the ceramic with x = 0.01 sintered at/above 960 °C located at the morphotropic phase boundary, large grains, good densification, high resistivity and enhanced electrical properties are obtained.     

Thermal stability and fire behavior of aluminum diethylphosphinate-epoxy resin nanocomposites

The flame retardancy of 2, 2-bis(4-glycidyloxyphenyl)propane (DGEBA)-aluminum diethylphosphinate (AlPi) nanocomposites (EP-AlPi/(P ? x), x = 1, 2, 3 %) was greatly enhanced by ultrasonic dispersion of nano-sized AlPi into epoxy resin. The UL 94 V-0 rating can be reached for EP-AlPi nanocomposites with a relatively low addition amount of AlPi (on the account of 8.4 wt% or phosphorus content of 2 wt%) as well as the LOI value over 37.2. The glass transition temperature (T _g) enhanced properties were investigated by DTA, which showed that: T _gs were about 5 °C higher than that of neat epoxy resin; T _g increased along with content increasing of AlPi. Based on TGA results under a non-isothermal condition, the thermal degradation kinetics of EP-AlPi/(P ? x) composites were studied by Kissinger’s, Ozawa’s, Flynn–Wall–Ozawa’s and Coast-Redfern’s methods, which suggested the conversion function f (α) = 1/2α ^?1 or f (α) = [?ln(1 ? α)]^?1 for EP-AlPi/(P ? 1 %); f (α) = [?ln(1 ? α)]^?1 for EP-AlPi/(P ? 2 %) and EP-AlPi/(P ? 3 %) during the investigated process. The epoxy resin nanocomposites obtained in this study are green functional polymers and will become flame retardant potential candidates in electronic fields such as printed wiring boards with high performance.     

Influence of the epoxidation degree of a polystyrene–polybutadiene–polystyrene (SBS) triblock copolymer on the compatibilization with an organomodified nanoclay

In this work, the addition of organophilic-modified montmorillonite into polystyrene–polybutadiene–polystyrene (SBS) triblock copolymers was investigated with and without the use of epoxidized SBS as a compatibilization agent. The nanocomposites were prepared by melting mixture at 60 rpm and 130 °C. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), tensile tests, and dynamic-mechanical analysis (DMA). XRD and TEM showed the formation of an intercalated dispersion of clay platelets oriented on the SBS surface. The AFM showed the typical lamellar microstructure of the styrene and butadiene phases of SBS. The estimation of the average distance between the styrene lamellae by AFM analysis showed that the platelets are anchored between the phases, and this structural feature caused an increase in elastic modulus. DMA analysis showed that the T _g of butadiene decreased in the nanocomposites. The decrease of the T _g and the increase in the elastic modulus are correlated to mechanisms at the micro- and the macro-scales, respectively. The decrease in the T _g indicates flexibilization at the interface, whereas the intercalation of the platelets restricted the interphase macroscale deformation.     

Study on low temperature sintering and electrical properties of CuO-doped Ca0.28Ba0.72Nb2O6 ceramics

Ca_0.28Ba_0.72Nb₂O₆ (CBN28) ceramics with different content of CuO were prepared by the conventional ceramic fabrication technique. The effects of CuO content on the phase structure, microstructure, dielectric and ferroelectric properties of obtained CBN28 ceramics were investigated. XRD results showed that pure tungsten bronze structure was obtained in all ceramics and CuO additive could accelerate the phase formation at lower temperatures. The CuO aid was effective for the uniform grain size in CBN28 ceramics, as it could facilitate the sintering behavior and suppress the anisotropic growth behavior obviously. The dielectric and ferroelectric properties of CBN28 ceramics depended greatly on the CuO content. Curie temperature T _c and dielectric loss tanδ both shifted downward, whereas the maximum dielectric constant ε _m and the dielectric constant around room temperature ε _r all increased initially and then decreased as x increased from 0.1 to 0.4 wt%. Normal ferroelectric hysteresis loops could be observed in all compositions, and the remnant polarization P _r decreased gradually. It was found that the comprehensive electric performance was optimized in CBN28-0.2 wt% CuO ceramics: ε _r = 453, ε _m = 3,371, T _c = 226 °C, tanδ = 0.048, P _r = 4.72 μC/cm² and E _c = 13.81 kV/cm, showed that CuO sintering aid could not only ameliorate the sintering behavior but also improve the electrical properties.     

Impurity-conditioned solid-solid transition in simple halides

Solid-solid transitions are well known for many simple halides. All of the rare earth fluorides, RF₃, with atomic number greater than that of Nd have been reported to crystallize to the hexagonal form at the melting temperature (T_mp), and subsequently invert to the orthorhombic form at some lower temperature (T_ss) (2). The temperature difference T_mp - T_ss = Δt reported in the literature (3) is 300°C for GdF₃, 124°C for DyF₃, and 73°C for HoF₃. Using GdF₃, DyF₃, and HoF₃, DTA measurements show T_ss (and therefore Δt) to be impurity-sensitive. Results indicate that the hydroxyl ion, OH^?, is the impurity. DTA measurements show Δt = 0 when OH^? concentration approaches zero. Moreover, crystal growth from the melt in a reactive atmosphere chosen to minimize OH^? directly yields the orthorhombic phase. Consequently, according to the phase rule, hexagonal orthorhomic is not an equilibrium process involving only one component at constant pressure. By minimizing OH^? concentration, large single crystals (>1 cm in length) of many halides previously thought to exhibit dimorphism have been grown from the melt.     

Comparison of a SiO2–CaO–ZnO–SrO glass polyalkenoate cement to commercial dental materials: glass structure and physical properties

Glass polyalkenoate cements (GPCs) have previously been considered for orthopedic applications. A Zn–GPC (BT 101) was compared to commercial GPCs (Fuji IX and Ketac Molar) which have a setting chemistry analogous to BT 101. Handling properties (working, T _w and setting, T _s times) for BT 101 were shorter than the commercial GPCs. BT 101 also had a higher setting exotherm (S _x —34 °C) than the commercial GPCs (29 °C). The maximum strengths for BT 101, Fuji IX, and Ketac Molar were 75, 238, and 216 MPa (compressive, σ _c), and 34, 54, and 62 MPa (biaxial flexural strengths, σ _f), respectively. The strengths of BT 101 are more suitable for spinal applications than commercial GPCs.     

Homoepitaxial growth of GaN single crystals using gallium hydride

The growth of gallium nitride (GaN) single crystals was performed using gallium hydride (GaH_x) as a Ga source. In this study, a GaN film with a smooth surface was obtained by homoepitaxial growth on a GaN film commercially produced by the Metal Organic Chemical Vapor Deposition (MOCVD-GaN). Photoluminescence spectrum of grown film revealed that GaN film obtained in this study shows excellent optical property. An increase in the growth rate was achieved with the amount of GaH_x (x = 1, 2, 3) supplied to the growth portion. The amount of GaH_x produced by a reaction between Ga and H₂ was increased with the residence time of H₂ in a Ga melt. The dependence of the growth rate and surface morphology on the growth condition was examined using Scanning Electron Microscopy (SEM).