Crystallization of LiNbO3 and NaNbO3 in niobiosilicate glass–ceramics

Although glass–ceramics have been widely explored for their thermal stability and mechanical properties, they also offer unique symmetry-dependent properties such as piezoelectricity and pyroelectricity through controlled crystallization of a polar phase. This work examines crystallization of LiNbO₃ in a 35SiO₂–30Nb₂O₅–35Li₂O mol% composition and crystallization of LiNbO₃ and NaNbO₃ in a 35SiO₂–30Nb₂O₅–25Li₂O–10Na₂O mol% composition. Crystallization kinetics are examined using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory where the Avrami exponent, n, is calculated to be 1.0–1.5. Microscopical analysis shows dendritic morphology, which when combined with the JMAK analysis, suggests diffusion-controlled one-dimensional growth. Adding Na₂O to the glass composition increases the inter-diffusivity of ions which causes LiNbO₃ to crystallize faster and lowers the activation energy of transformation from 1054 ± 217 kJ/mol in the ternary composition to 882 ± 212 kJ/mol. Time-temperature-transformation diagrams are presented which show that the temperature for maximum rate of transformation for LiNbO₃ is ∼650°C and for NaNbO₃ is ∼715°C.     

Different kinetic in incorporation and depletion of n−3 fatty acids in erythrocytes and leukocytes of mice

n−3 PUFA are well known for their anti-inflammatory effects. However, there has been only limited study on the kinetics of incorporation and depletion of n−3 PUFA in immune cells. In the present study we investigated the incorporation and depletion of n−3 PUFA in erythrocytes and leukocytes in mice during a 6-wk feeding period. Over the first 3-wk period (the incorporation period) the mice were fed a special diet with a high n−3/n−6 PUFA ratio. In the following 3-wk period (the depletion period) the mice were fed a standard chow diet. A linear incease of the concentration of EPA and DHA in erythrocyte membranes was observed during the incorporation period, whereas a stagnation was observed after the second week for leukocytes. The level of EPA did not fall to the background level after the depletion period, and the level of DHA was kept almost constant during the depletion period in the erythrocyte membranes. In leukocytes the concentration of both EPA and DHA decreased during the depletion period, but did not reach the background level after the 3-wk depletion. In conclusion, the kinetics of EPA and DHA in the different cells are different. The rate of incorporation is faster than that of depletion for n−3 PUFA. More n−3 PUFA can be incorporated into leukocytes in comparison with erythrocytes. The ratio of n−3/n−6 PUFA is more important than the amount of n−3 FA in changing the FA compositions of membrane lipids.     

Chemical Reactions between CaZrO3 and SiC in Ar Atmosphere

The Chemical reactions between CaZrO3-SiC at high temperature (1200℃－1600℃） in Ar atmosphere have been investigated.The results have indicated that at high temperatures,chemical reactions would occur between CaZrO3 and SiC;the reaction products would change with increas of temperature.In Ar atmosphere CaZrO3 and SiC will react when the temperature reaches 1300℃，At 1300℃－1400℃ ZrC is formed ;above 1400℃ ZrC is transformed to ZrO.     

Optimized electric-energy storage in BiFeO3–BaTiO3 ceramics via tailoring microstructure and nanocluster

This study demonstrates the high energy-storage performance using 0.1 wt% MnO₂–added 0.7(Bi_1?xSm_xFeO₃)? 0.3(BaTiO₃) (x = 0–0.3) ceramics through tailoring microstructures and polar order. Sequential structure transitions were identified from a co-occurrence of nonpolar pseudo-cubic Pm-3m and ferroelectric rhombohedral R3c symmetries to antipolar orthorhombic Pbam and nonpolar orthorhombic Pnma symmetries as Sm substitution increases. Recoverable energy densities (W_rec) of 4.5 J/cm³ and 4.1 J/cm³ with efficiencies (η) of 62.1% and 78.1% were achieved respectively for x = 0.15 and 0.2 at a field of 220 kV/cm. The improved energy storage is associated with microstructure modification and complex grain matrix, consisting of grain boundaries, nanocluster/nanomosaic structures, core-shell structures, and polar nanoregions. The nanocluster/nanomosaic structures may act as barriers to suppress polar order and enhance dielectric breakdown strength. This work provides an efficient route to utilize binary BiFeO₃-BaTiO₃ ceramics for electrical energy storage.     

Grain-boundary segregation and precipitates in La2O3 and Pr2O3 doped SnO2·CoO-based varistors

Structural heterogeneities in SnO₂·CoO-based varistors were analyzed by transmission electron microscopy. In SnO₂·CoO-based system doped with La₂O₃ and Pr₂O₃ two kinds of precipitate phases at grain boundary region were found. Using energy dispersive spectrometry they were found to be Co₂SnO₄ and Pr₂Sn₂O₇, presenting a defined crystalline structure. It was also identified that such precipitate phases are mainly located in triple-junctions of the microstructure. HRTEM analysis revealed the existence of other two types of junctions, one as being homo-junctions of SnO₂ grains and other due to twin grain boundaries inside the SnO₂·CoO grain. The role of these types of junction in the overall nonlinear electrical features is also discussed.     

Dielectric properties and related ferroelectric domain configurations in multiferroic BiFeO3–BaTiO3 solid solutions

Dielectric properties and ferroelectric domain configurations of multiferroic xBaTiO₃–(1 ? x)BiFeO₃ (x = 0.10–0.33) solid solutions synthesized by conventional solid-state reaction, were reported. A structural transition from rhombohedral to pseudo-cubic structures appeared around x = 0.33, and the formation of impurity phase of Bi₂Fe₄O₉ was effectively depressed by doping BaTiO₃. Dielectric constants of xBaTiO₃–(1 ? x)BiFeO₃ solid solutions decreased with increasing the frequency, and the degree of decrease was related to the doping content of BaTiO₃. Transmission electron microscopy images revealed that the ferroelectric domain configurations in the multiferroic BiFeO₃–BaTiO₃ solid solutions with rhombohedral symmetry, exhibited a wavy character whereas a predominant intricate domain structure with fluctuating mottled contrast was observed in the multiferroic BiFeO₃–BaTiO₃ solid solution with pseudo-cubic phase structure. The presence of 1/2{1 1 1} superlattice spots in the selected area electron diffraction patterns taken from the multiferroic BiFeO₃–BaTiO₃ solid solutions with rhombohedral symmetry indicated that the ordered regions have a doubled perovskite unit cell.     

Dietary intakes and food sources of n−6 and n−3 PUFA in french adult men and women

The intake of individual n−6 and n−3 PUFA has been estimated in 4,884 adult subjects (2,099 men and 2,785 women), volunteers from the French SU.VI.MAX intervention trial. The food intakes of each subject were recorded in at least ten 24-h record questionnaires completed over a period of 2.5 yr, allowing the estimation of the daily intake of energy; total fat; and linoleic, α-linolenic, arachidonic, eicosapentaenoic (EPA), n−3 docosapentaenoic (DPA), and docosahexaenoic (DHA) acids. The mean total fat intake corresponded to 94.1 g/d (36.3% of total energy intake) in men and 73.4 g/d (38.1% of energy) in women. The intake of linoleic acid was 10.6 g/d in men and 8.1 g/d in women, representing 4.2% of energy intake; that of α-linolenic acid was 0.94 g/d in men and 0.74 g/d in women, representing 0.37% of energy intake, with a mean linoleic/α-linolenic acid ratio of 11.3. The mean intakes of long-chain PUFA were: arachidonic acid, 204 mg/d in men and 152 mg/d in women; EPA, 150 mg/d in men and 118 mg/d in women; DPA, 75 mg/d in men and 56 mg/d in women; DHA, 273 mg/d in men and 226 mg/d in women; long-chain n−3 PUFA, 497 mg/d in men and 400 mg/d in women. Ninety-five percent of the sample consumed less than 0.5% of energy as α-linolenic acid, which is well below the current French recommendation for adults (0.8% of energy). In contrast, the mean intakes of long-chain n−6 and n−3 PUFA appear fairly high and fit the current French recommendations (total long-chain PUFA: 500 mg/d in men and 400 mg/d in women; DHA: 120 mg/d in men and 100 mg/d in women). The intakes of α-linolenic acid, and to a lesser extent of linoleic acid, were highly correlated with that of lipids. Whereas the main source of linoleic acid was vegetable oils, all food types contributed to α-linolenic acid intake, the main ones being animal products (meat, poultry, and dairy products). The main source of EPA and DHA (and of total long-chain n−3 PUFA) was fish and seafood, but the major source of DPA was meat, poultry, and eggs. Fish and seafood consumption showed very large interindividual variations, the low consumers being at risk of insufficient n−3 PUFA intake.     

Structures and temperature-dependent electrical properties in Ba0.8Sr0.2TiO3–BiAlO3 electrostrictive ceramics

Lead-free piezoceramics of (1 ? x)Ba_0.8Sr_0.2TiO₃–xBiAlO₃ [(1 ? x)BST–xBA (0 ≤ x ≤ 0.12)] have been synthesized and the structures and properties have been investigated systemically. X-ray diffraction patterns indicated that the solid solution limit is close to x = 0.04, and a morphotropic phase boundary (MPB) separating tetragonal and pseudocubic phases exists near x = 0.02. The ferroelectricity weakens monotonously with increasing x, accompanied by weakened butterfly shaped bipolar strain–electric field curves. The temperature dependent properties of the composition with x = 0.02 have been typically investigated, showing that with increasing temperature, the ferroelectricity tends to be weakened. Pure electrostrictive effect has been found in the compositions with x = 0.02 and 0.03 close to room temperature temperature. Based on the results, the effects of BA on structures and electric properties were discussed.     

Nuclear γ-resonance spectra and local surrounding of 121Sb and 129I atoms in CuI-PbI2-As2Se3 and CuI-SbI3-PbI2-As2Se3 films

The local surrounding of copper, antimony, and iodine atoms in multicomponent chalcogenide films CuI-PbI₂-As₂Se₃ and CuI-SbI₃-PbI₂-As₂Se₃ deposited from solutions of chalcogenide glass in n-butylamine has been studied by the Mössbauer spectroscopy method on ¹²¹Sb and ¹²⁹I isotopes. It was established that antimony atoms are in the Sb (III) state, where each antimony atom is surrounded by three selenium atoms. Copper atoms are in the Cu (I) state and are surrounded by iodine atoms. The local surrounding of copper, antimony, and iodine atoms in chemically deposited chalcogenide films is analogous to the local surrounding of atoms in the initial chalcogenide glass.     

Irradiation damage in xenon-irradiated α-Al2O3 before and after annealing

The irradiation damage build-up of α-Al₂O₃ under Xe²⁰⁺ ion irradiation has been investigated by a combination of Raman spectroscopy and transmission electron microscopy. α-Al₂O₃ crystalline was irradiated with 5 MeV Xe²⁰⁺ ions to fluences of 1 × 10¹⁴ cm⁻², 5 × 10¹⁴ cm⁻², 1 × 10¹⁵ cm⁻² and 5 × 10¹⁵ cm⁻² at room temperature. No amorphous phase was formed under the experimental condition. The Raman intensities of feature peaks of Al₂O₃ decrease after Xe ion irradiation. The interstitial-type dislocation loops with Burgers vectors of b = 1/3 < 10-11> on the {10-10} and (0001) habit planes were found. The formation of basal and prism dislocation loops is related to the lattice damage and position. After annealing, the Raman intensities of feature peaks of Al₂O₃ increases with annealing temperature. With annealing at 1500℃ for 30 min, lattice defects were completely annealed out in the near surface region. Meanwhile, long dislocations and facet cavities on long dislocations were found in the Xe deposition region. Some lattice defects beyond the projected region were found due to the diffusion toward deep region during thermal annealing.     

Oxidation Behaviour of Si3N4 Materials in Air and Nitrogen Atmosphere

Si3N4 powder and hot-pressed Si3N4 ceramics added with Al2O3 are used for investigate their oxidation behvior in air and nitrogen atmosphere(with oxygen partial pressure PO2=1-10Pa),The oxidation products of Si3N4 are examined by chemical analysi,X-ray diffraction (XRD) and XPS method,Also, thermodynamic calculation is made to analyze oxidation behavior of Si3N4.The results show that only passive oxidation will occur when Si3N4 is oxidized in air at high temperature,whereas in N2 at high temperature,the active oxidation is dominant in spite of the existence of a little passive oxidation.     

Corrosion protection of steel in molten Li2CO3–K2CO3 and Na2CO3–K2CO3 mixtures in a hydrogen-containing atmosphere

The electrochemical behaviour of TiN-, TiN–AlN-, Cr- and CrN-coated 316L stainless steel in molten Li₂CO₃–K₂CO₃ and Na₂CO₃–K₂CO₃ melts in a reducing gaseous atmosphere (10% H₂–90% N₂) was studied using voltammetry and scanning electron microscopy combined with energy-dispersed X-ray analysis in the temperature range of 600–730 C. To facilitate the identification of the electrochemical reactions the voltammetric behaviour of stainless steel, titanium, nickel and gold was also investigated. Voltammetric characteristics obtained at AlN–TiN coated electrodes showed no anodic reactions at potentials more negative than that of CO^2– ₃ oxidation. Cr- and CrN-coated electrodes demonstrated a suppressed anodic dissolution after the first steady state voltammetric cycle. The voltammograms obtained for the other electrodes studied displayed the corresponding anodic metal-dissolution waves. TiN, AlN, Cr and CrN coatings seem to be the most promising as corrosion-resistant materials for the anodic compartments of molten carbonate fuel cells.     

Distinct Dynamic and Conformational Features of Human STING in Response to 2′3′-cGAMP and c-di-GMP

The human stimulator of interferon genes protein (hSTING) can bind cyclic dinucleotides (CDNs) to activate the production of type I interferons and inflammatory cytokines. These CDNs can be either bacterial secondary messengers, 3′3′-CDNs, or endogenous 2′3′-cGAMP. cGAMP, with a unique 2′–5′ bond, is the most potent activator of hSTING among all CDNs. However, current understanding of the molecular principles underlying the unique ability of 2′3′-cGAMP to potently activate hSTINGs other than 3′3′-CDNs remains incomplete. In this work, molecular dynamics simulations were used to provide an atomistic picture of the binding of 2′3′-cGAMP and one 3′3′-CDN (c-di-GMP) to hSTING. The results suggest that hSTING binds more strongly to 2′3′-cGAMP than to c-di-GMP, which prefers to bind with a more open and flexible state of hSTING. Finally, a potential “dock–lock–anchor” mechanism is proposed for the activation of hSTING upon the binding of a potent ligand. It is believed that deep insights into understanding the binding of hSTING with 3′3′-CDNs and the endogenous 2′3′-cGAMP would help to establish the principles underlying powerful 2′3′-cGAMP signaling and the nature of hSTING activation, as well as related drug design.     

Synthesis of high purity Li_2CO_3 and MgCO_3·3H_2O in a homogeneous-like organic phase

Herein, three kinds of Li_2CO_3 and two kinds of MgCO_3·3H_2O crystals are easily synthesized in a homogeneouslike organic phase. The morphology and size of synthesized crystals are controllable and adjustable in the single organic phase, with the morphology of Li_2CO_3 ranging from micro-flaky, flower to nanobranch, MgCO_3·3H_2O ranging from nanosphere to nanorod. Compared with coupled reaction and solvent extraction process, of which the crystallization process occurred in the interface of two phase, our proposed method made it possible that the crystallization process occurred in the single organic phase, which resulted in better crystal morphology.Moreover, the formation mechanism of different crystal morphologies is discussed, the results showed that the crystals in micron size and nano size are involved in two crystallization mechanism, the micron particles in the form of flake and flower-like is a typical radial growth, which means that the growth occurs by diffusion around a nucleus as starting point, while the reaction model for small particles should be similar to a water-in-oil structure. As the reaction carried out, the crystal should be restricted in a constrained organic structure.     

High piezoelectric properties in 0.7BiFeO3–0.3BaTiO3 ceramics with MnO and MnO2 addition

BiFeO₃–BaTiO₃–based solid solutions are promising candidates for high–temperature piezoelectric devices because of their high Curie temperature (T_C) and considerable electrical properties. Here, we reported an optimum composition of 0.7Bi(Fe_0.999Mn_0.001)O₃–0.3BaTiO₃ ceramic with a large piezoelectric constant (d₃₃) of 230 pC/N and a high T_C of 505 °C, which was attributed to the intentional introducing of the ceramic with MnO and MnO₂ mixture. Furthermore, an in situ d₃₃ measurement was carried out, demonstrating excellent thermal stability for the 0.7Bi(Fe_0.999Mn_0.001)O₃–0.3BaTiO₃ specimen. The d₃₃ remained above 200 pC/N in the temperature range of 25 °C–400 °C and its fluctuation was less than ± 15 %. It was determined that the high d₃₃ in the 0.7BiFe_0.999Mn_0.001)O₃–0.3BaTiO₃ ceramic originated from a synergistic effect of rhombohedral distortion, intrinsic response, and ferroelectric order. The findings establish a solid correlation between electrical properties and phase/domain structure, and provide a novel approach to improve the piezoelectric properties for BiFeO₃–BaTiO₃–based ceramics.     

Synthesis and Properties of Fusion-Cast Refractories in the Al2O3 – B2O3 System

Synthesis and properties of fusion-cast high-alumina refractories in the Al₂O₃ – B₂O₃ system are reported. Adding B₂O₃ is shown to improve density and fabricability of the fusion-cast products. As shown by x-ray diffractometry and petrographic analysis, the phase composition of synthetic products is represented by corundum and 9Al₂O₃ 2B₂O₃ boroaluminate. Corrosion tests in molten industrial glasses have shown the potential use of these materials in the melting technology of VS-92-grade optical lead silicate glass.     

Domain structure and evolution in ZnO-modified Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 ceramics

The doping of ZnO is efficient to improve the piezoelectric property and thermal stability of Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PMN–PT) based ceramics. However, the underlying physics, especially the local domain structures of the ZnO modified PMN–PT ceramics, which is strongly associated with the electric properties, is not clear yet. In this paper, we investigated the local domain structures and their evolution as a function of x in PMN–0.32PT:xZnO ceramics. It was found that, the domain evolution is mainly caused by the growth of grain size induced by the sintering aiding effect of ZnO at x < 0.04, and the domain evolution can be attributed to the phase transition induced by the partial replacement of Mg²⁺ by Zn²⁺ in the B-site of PMN–PT lattice at x > 0.06. Furthermore, we also investigated the domain structure evolution as functions of temperature and local external electric field in PMN–0.32PT:0.06ZnO ceramics, which exhibited superior piezoelectric property relative to other compositions. We found that the irregular nanodomains are more stable at high-temperature range, and the regular non-180° domains exhibited more complex rotation behavior under local electric field, which probably leads to the thermal stability and piezoelectric property enhancement in the ZnO-modified PMN–0.32PT ceramics.     

Mandelshtam–Brillouin Scattering in As2S3 and GeS2 Chalcogenide Glasses

Mandelshtam–Brillouin and Rayleigh scattering in As₂S₃ and GeS₂ chalcogenide glasses is investigated. Longitudinal hypersonic velocities, adiabatic elastooptical constants (p ₁₂) _ad at frequencies 15 GHz, extinction coefficients, and scattering losses are determined.