Structure and electrical conductivity relaxation studies of Nb2O5-doped B2O3–Bi2O3–LiF glasses

Glasses with composition (70 − x) B₂O₃·15Bi₂O₃·15LiF·xNb₂O₅ with x = 0–1.0 mol% were prepared by conventional glass-melting technique. The molar volume V _m values decrease and the glass transition temperatures T _g increase with increase of Nb₂O₅ content up to 0.2 mol%, which indicates that Nb⁵⁺ ions act as a glass former. Beyond 0.2 mol% Nb₂O₅ the V _m increases and the T _g decreases, which suggests that Nb⁵⁺ ions act as a glass modifier. The FTIR spectra suggest that Nb⁵⁺ ions are incorporated into the glass network as NbO₆ octahedra, substituting BO₄ groups. The temperature dependence of the dc conductivity follows the Greaves variable range hopping model below 454 K, and follows the small polaron hopping model at temperatures >454 K. σ _dc, σ _ac conductivity and dielectric constant (ε) decrease and activation energy for dc conduction ΔE _dc which increases with increasing Nb₂O₅ content up to 0.2 mol%, whereas σ _dc, σ _ac and (ε) increase and ΔE _dc decreases with increasing Nb₂O₅ content beyond 0.2 mol%. The impedance spectroscopy shows a single semicircle or arcs which indicate only the ionic conduction mechanism. The electric modulus formalism indicates that the conductivity relaxation is occurring at different frequencies exhibit temperature-independent dynamical process. The (FWHM) of the normalized modulus increases with increase in Nb₂O₅ content suggesting that the distribution of relaxation times is associated with the charge carriers Li⁺ or F⁻ ions in the glass network.     

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.     

Giant electrical conductivity enhancement in BaO–V2O5–Bi2O3 glass by nanocrystallization

The effects of the annealing of 20BaO–30V₂O₅–50Bi₂O₃ glass on the structural and electrical properties were studied by scanning electron micrographs (SEM), X-ray diffraction (XRD), differential scanning calorimeter (DSC) density (d) and dc conductivity (σ). The XRD and SEM observations have shown that the sample under study undergoes structural changes: from amorphous at the beginning, to partly crystalline after nanocrystallization at crystallization temperature (T_c) for 1 h and to colossal crystallization after the annealing at the same temperature for 24 h. The average size of these grains after nanocrystallization at T_c for 1 h was estimated to be about 25–35 nm. However, the glass heat treated at T_c = 580 °C for 24 h the microstructure changes considerably. The nanomaterials obtained by nanocrystallization at T_c for 1 h exhibit giant improvement of electrical conductivity up to four order of magnitude and better thermal stability than the as-received glass. The major role in the conductivity enhancement of this nanomaterial is played by the developed interfacial regions “conduction tissue” between crystalline and amorphous phases, in which the concentration of V⁴⁺–V⁵⁺ pairs responsible for electron hopping is higher than inside the glassy matrix. The annealing at T_c for 24 h leads to decrease of the electronic conductivity. This phenomena lead to disappearance of the abovementioned “conduction tissue” for electrons and substantial reduction of electronic conductivity. The high temperature (above θ/2) dependence of conductivity could be qualitatively explained by the small polaron hopping (SPH) model. The physical parameters obtained from the best fits of this model are found reasonable and consistent with the glass compositions.     

Densification and dielectric properties of SrO–Al2O3–B2O3 ceramic bodies

The influence of SrO (0·0–5·0 wt%) on partial substitution of alpha alumina (corundum) in ceramic composition (95 Al₂O₃–5B₂O₃) have been studied by co-precipitated process and their phase composition, microstructure, microchemistry and microwave dielectric properties were studied. Phase composition was revealed by XRD, while microstructure and microchemistry were investigated by electron-probe microanalysis (EPMA). The dielectric properties by means of dielectric constant (ε _r ), quality factor (Q × f) and temperature coefficient of resonant frequency (τ _f ) were measured in the microwave frequency region using a network analyser by the resonance method. The addition of B₂O₃ and SrO significantly reduced the sintering temperature of alumina ceramic bodies to 1600 °C with optimum density (∼ 4g/cm³) as compared with pure alumina powders recycled from Al dross (3·55g/cm³ sintered at 1700 °C).     

Bi2O3助熔剂对CaO-B2O3-SiO2/Al2O3玻璃陶瓷复合材料性能的影响

以CaO-B₂O₃-SiO₂(CBS)玻璃粉体和Al₂O₃陶瓷粉体为原料,通过在CBS与Al₂O₃的质量比固定为50:50的玻璃-陶瓷复合材料中添加适量的Bi₂O₃作为烧结助熔剂,探讨了Bi₂O₃助熔剂对CBS/Al₂O₃复合材料的烧结性能、介电性能、抗弯强度和热膨胀系数的影响规律.研究表明:Bi₂O₃助熔剂能通过降低CBS玻璃的转变温度和黏度促进CBS/Al₂O₃复合材料的致密化进程,于880 ℃下烧结即能获得结构较致密、气孔较少的CBS/Al₂O₃复合材料.然而,过量添加Bi₂O₃将使玻璃的黏度过低,从而恶化CBS/Al₂O₃复合材料的烧结性能、介电性能及抗弯强度.当Bi₂O₃的添加量为CBS/Al₂O₃复合材料的1.5wt%时,于880 ℃下烧结即能获得最为致密的CBS/Al₂O₃复合材料,密度为2.82 g·cm^-3,这一材料具有良好的介电性能(介电常数为7.21,介电损耗为1.06×10^-3),抗弯强度为190.34 MPa,0~300 ℃的热膨胀系数为3.52×10^-6 K^-1.     

Glass formation and third-order optical nonlinear characteristics of bismuthate glasses within Bi2O3–GeO2–TiO2 pseudo-ternary system

Glass-forming region of Bi₂O₃–GeO₂–TiO₂ (BGT) pseudo-ternary system was determined by using melt-quench method. A series of high transparent glass samples were selected and their structural characteristics were investigated by FT-IR and Raman spectra. By employing Z-scan and optical Kerr shutter techniques with femtosecond laser pulses as excitation source, third-order optical nonlinearities (TON) of the BGT glasses as well as the TON response time were investigated at wavelength of 800 nm. The ultrafast nonlinear response and high figure of merit suggest great potentials of BGT glasses in applications of all-optical switching or related optical devices.     

Bi2O3-TiO2复合氧化物光催化环己烷选择氧化

环己烷选择性氧化生成的环己醇和环己酮是己内酰胺合成中的重要中间体,在尼龙生产中具有重要作用,但工业路线条件苛刻,效率低。温和条件下环己烷选择性氧化引起极大关注,而光催化在低温环境压力下的饱和 C-H 活化和氧化具有独特优势。本文采用水热法制备了一系列 Bi₂O₃-TiO₂复合催化剂,对其结构、形貌、光学与光电化学性质通过多种方法包括 SEM、XRD、N₂吸脱附、UV-Vis、光致发光光谱、瞬态光电流响应等进行详细表征。在室温、0.1 MPa 氧气为氧化剂、500 W 氙灯模拟太阳光条件下比较了纯 TiO₂、Bi₂O₃ 和 Bi₂O₃-TiO₂ 复合物对环己烷选择性氧化的催化性能,结果表明,复合 Bi₂O₃ 后提高了 TiO₂ 的催化活性,其中 9%Bi₂O₃-T...     

液相沉淀法制备球状Bi2O3粉料

以金属铋为原料,溶解在硝酸中,配置成Bi(NO3)3溶液,用NH3-NH4HCO3作沉淀剂,调节pH值,制备Bi2O3粉料.通过控制反应温度、加料速度、反应时间以及加入适量的分散剂,制备得粒径为2～3μm、粒度分布均匀、分散性良好的超细球状Bi2O3粉料.用Bi2O3粉料制备的ZnO压敏电阻,具有压比低,方波冲击合格率高,性能一致等优点.     

Synthesis and properties of magnetic solid superacid: SO4/ZrO2–B2O3–Fe3O4

A magnetic SO₄²⁻/ZrO₂–B₂O₃–Fe₃O₄ solid superacid catalyst is prepared via a simple chemical co-precipitation approach. The obtained materials were characterized in detailed by X-ray powder diffraction, thermogravimetric analysis–different scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), electron microscopy (SEM and TEM), and Mossbauer spectra. Powder X-ray diffraction patterns show that in this composite oxide the transformation temperature of ZrO₂ from tetragonal to monoclinic phase is higher compared to the pristine SO₄²⁻/ZrO₂ material. The introduction of Fe₃O₄ endows the superacid with a super-paramagnetic property while in a ferromagnetic state after calcination. The superacid exhibits high catalytic activity in forming ethyl acetate by esterification.     

Preparation and characterization of Y2O3–Sm2O3 co-doped ceria electrolyte for IT-SOFCs

Y₂O₃–Sm₂O₃ co-doped ceria (YSDC) powder was synthesized by a gel-casting method using Ce(NO₃)₃·6H₂O, Sm₂O₃ and Y₂O₃ as raw materials. Phase structure of the synthesized powders was characterized by X-Ray diffraction analysis. Sinterability of the powders was investigated by testing the relative density and observing the microstructure of the sintered YSDC samples. Electrical conductivity of the sintered YSDC samples was measured using impedance spectra method. Single solid oxide fuel cells based on the YSDC electrolyte were also assembled and tested. The results showed that YSDC powders with single-phase fluorite structure can be obtained by calcining the dried gelcasts at temperature above 800 °C. Average particle size of the YSDC powder is 50–100 nm. Relative density of more than 95% of the theoretical can be achieved by sintering the YSDC compacts at temperature above 1400 °C. The sintered YSDC sample has an ionic conductivity of 4.74 × 10⁻² S cm⁻¹ at 800 °C in air. Single fuel cells based on the YSDC electrolyte with 50 μm in thickness were tested using humidified hydrogen as fuel and air as oxidant, and maximum power densities of about 190 and 112 mW cm⁻² were achieved at 700 and 600 °C, respectively.     

Low-Magnetoresistance RuO2–Al2O3 Thin-Film Thermometer and its Application

Thermometers consisting of RuO₂–Al₂O₃ composite thin films were prepared by RF sputtering. It was found that different electrode-patterning techniques have dissimilar effects on the magnetoresistance (MR) and the temperature coefficient of resistance (TCR). In general, the thermometers with electrodes fabricated by photo-resist lithography exhibit superior performance compared to those with electrodes prepared using a metal mask. By adjusting the relative compositions of RuO₂ and Al₂O₃, the thermometers can be applied to a wide temperature range from 60 mK to 500 K. In a pulsed magnetic field up to 55 T, the MR at 4.2 K of a typical thermometer for the temperature range from 1.4 K to 300 K increases linearly with magnetic field to a maximum of ~15 %, corresponding to a temperature deviation of ~−4 %. As frequency increases from dc to 1.9 MHz, the MR decreases from  −13 % to ~ − 0.5 % at T = 1.3 K and H = 55 T. By integrating the thermometer with a heater on a sapphire chip, a micro-calorimeter can be developed and successfully used to measure the heat capacity of small mg-sized sample. The RuO₂–Al₂O₃ composite film can also be employed as an infrared bolometer operated at room temperature.     

Effects of copper and Al2O3 particles on characteristics of Cu–Al2O3 composites

High-energy milling was used for production of Cu–Al₂O₃ composites. The inert gas-atomized prealloyed copper powder containing 2 wt.%Al and the mixture of the different sized electrolytic copper powders with 4 wt.% commercial Al₂O₃ powders served as starting materials. Milling of prealloyed copper powders promotes formation of nano-sized Al₂O₃ particles by internal oxidation with oxygen from air. Hot-pressed compacts of composites obtained from 5 and 20 h milled powders were additionally subjected to the high-temperature exposure in argon at 800 °C for 1 and 5 h. Characterization of processed material was performed by optical and scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness, as well as density and electrical conductivity measurements. Due to nano-sized Al₂O₃ particles microhardness and thermal stability of composite processed from milled prealloyed powders are higher than corresponding properties of composites processed from the milled powder mixtures. The results were discussed in terms of the effects of different size of starting copper powders and Al₂O₃ particles on the structure, strengthening of copper matrix, thermal stability and electrical conductivity of Cu–Al₂O₃ composites.     

网状结构Bi2O3光催化剂的合成及其光催化性能

以Bi(NO3)3·5H2O为原料,天然棉花为模板结合热处理工艺,成功合成了具有网状结构的三斜晶相Bi2O3光催化材料,利用XRD、SEM、TG-DTA和UV-Vis漫反射等技术对样品的晶型结构、形貌及吸光性能等进行了表征。以亚甲基蓝染料分子模拟环境污染物,考察了样品的光催化性能。结果表明,棉花纤维在网状Bi2O3的制备中起到了充分的诱导作用,这种网状结构是由一些直径不一的Bi2O3扁平状网线交错排列、稀疏盘结而形成。TGA分析结果表明,适当的热处理在去除棉花模板的同时可以实现Bi 3+→Bi2O3的转化。在可见光照射下,网状Bi2O3的光催化活性及重复使用性能均优于粉体Bi2O3,反应100min后,对MB的脱色率可达到93%左右,并且重复使用4次后仍可使MB的脱色率保持在85%以上。此外,对网状Bi2O3的形成机理进行了探讨。     

Structure and electrical properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BiCoO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBiCoO₃ (x = 0.12–0.24, y = 0–0.04) have been fabricated by a conventional solid-state reaction method, and their structure and electrical properties have been investigated. The XRD analysis shows that samples with y ≤ 0.03 exhibit a pure perovskite phase and very weak impurity reflections can be detected in the sample with y = 0.04. With x increasing from 0.12 to 0.24 and y increasing from 0 to 0.04, the ceramics transform gradually from a rhombohedral phase to a tetragonal phase and rhombohedral–tetragonal phase coexistence to a pseudocubic phase, respectively. The morphotropic phase boundary (MPB) of the system between rhombohedral and tetragonal locates in the range of x = 0.18–0.21, y = 0–0.03. The ceramics near the composition of the MPB have good performances with piezoelectric constant d ₃₃ = 156 pC/N and electromechanical coupling factor k _p = 0.34 at x = 0.21 and y = 0.01, which attains a maximum value in this ternary system. Adding content of BiCoO₃ leads to a disappearance of the response in the curves of dielectric constant-temperature to the ferroelectric–antiferroelectric transition. The temperature dependence of dielectric properties suggests that the ceramics are relaxor ferroelectrics. The results show that (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBiCoO₃ ceramics are good candidate for use as lead-free ceramics.     

Relaxation process in PbI2–Ag2O–V2O5–B2O3 system: Dielectric,AC conductivity and modulus studies

Silver ion conducting super-ionic glass system xPbI₂–(100 − x) [Ag₂O–2(V₂O₅–B₂O₃)], where, 5 ≤ x ≤ 25, were prepared via melt quenching route and -characterized by XRD and DSC. Their electrical properties were measured by impedance spectroscopy in the frequency range of 2 MHz to 20 Hz from 30 to 120 °C. The electrical relaxation mechanism has been studied using AC conductivity, dielectric modulus function and frequency dependent dielectric permittivity over a wide range of frequency and temperature. Two different scaling approaches for AC conductivity as well as dielectric permittivity spectra were used to understand the nature of relaxation processes.     

Thermal properties and crystallization of PbO–MoO3–P2O5 glasses

Thermal properties and crystallization of glasses from PbO–MoO₃–P₂O₅ ternary system were studied in three compositional series (100 − x)[0.5PbO–0.5P₂O₅]–xMoO₃ (A), 50PbO–yMoO₃–(50 − y)P₂O₅ (B), and (50 − z)PbO–zMoO₃–50P₂O₅ (C). Glass transition temperature, crystallization temperature, coefficient of thermal expansion, and dilatation softening temperature of the studied glasses were determined by differential thermal analysis and dilatometry. Crystallization products of annealed glass samples were investigated by X-ray diffraction and Raman spectroscopy. X-ray diffraction analysis of crystallized glasses revealed the formation of PbP₂O₆, Pb₃P₄O₁₃, and PbMoO₄ in the samples of the B series. In the series A and C in the samples with a high MoO₃ content, crystalline compounds of Pb(MoO₂)₂(PO₄)₂ and (MoO₂)(PO₃)₂, respectively, were identified. Raman spectra of crystalline samples confirmed the results of X-ray diffraction measurements and provided also information on thermal stability of glasses and formation of glass-crystalline phases in the studied glass series.     

Crystallization and magnetic properties of a 10Li2O–9MnO2–16Fe2O3–25CaO–5P2O5–35SiO2 glass

The crystallization behavior and magnetic properties of 10Li₂O–9MnO₂–16Fe₂O₃–25CaO–5P₂O₅–35SiO₂ (10LFS) glass have been studied using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) to observe the crystallization behavior and a superconducting quantum interference device (SQUID) for measurements of the magnetic properties. The DTA shows that the 10LFS glass has one broad exothermic peak at approximately 674 °C and one sharp (the highest) exothermic peak at 764 °C. When the 10LFS glass crystallized at 850 °C for 4 h, the crystalline phases identified by XRD were lithium silicate (Li₂SiO₃), β-wollastonite (β-CaSiO₃), lithium orthophosphate (Li₃PO₄), magnetite (FeFe₂O₄) and triphylite (Li(Mn_0.5Fe_0.5)PO₄). The SEM surface analysis revealed that the β-wollastonite and lithium silicate have a lath morphology. The TEM microstructure examination showed that the largest FeFe₂O₃ particles have a size of approximately 0.3 μm. When the 10LFS glass was heat treated at 850 °C for 16 h and a magnetic field of 1000 Oe was applied, a very small remnant magnetic induction of 0.01 emu g⁻¹ and a coercive force of 50 Oe were obtained, which revealed an inverse spinel structure.     

A simple method for fabricating p–n junction photocatalyst CuFe2O4/Bi4Ti3O12 and its photocatalytic activity

The synthesis of Bi₄Ti₃O₁₂ and CuFe₂O₄ powders was achieved using a conventional solid-state reaction and the Sol–Gel method, respectively. A novel p–n heterojunction photocatalyst CuFe₂O₄/Bi₄Ti₃O₁₂ was subsequently prepared through ball milling. The structures, morphologies, and optical properties of the photocatalysts were comprehensively characterized. The transmission electron microscopy (TEM) images showed a clear interface between CuFe₂O₄ and Bi₄Ti₃O₁₂, indicating that a heterojunction between CuFe₂O₄ and Bi₄Ti₃O₁₂ was formed during ball milling. In addition, the photocatalytic activity was evaluated based on the photocatalytic degradation of methyl orange (MO). The results indicated that the photocatalytic activity of the p–n heterojunction photocatalyst CuFe₂O₄/Bi₄Ti₃O₁₂ was higher than that of Bi₄Ti₃O₁₂ alone. The enhanced photocatalytic activity could be attributed to the formation of a heterojunction between CuFe₂O₄ and Bi₄Ti₃O₁₂, which suppressed the recombination of photogenerated electron–hole pairs. We also investigated the effects of procedure time and dispersant (H₂O) during ball milling on the photocatalytic activity. The mechanisms underlying the observed photocatalytic activity were also described based on the semiconductor energy band theory and p–n junction principle. Moreover, the analysis of the radical scavengers confirmed that •O₂⁻ and h⁺ were the primary reactive species to cause the degradation of the MO.     

Investigation on the phase stability,sintering and thermal conductivity of Sc2O3–Y2O3–ZrO2 for thermal barrier coating application

Rare earth oxides co-doped zirconia have been developed for application in thermal barrier coating systems to promote the performance and durability of gas turbines. 8 mol%Sc₂O₃, 0.6 mol%Y₂O₃–stabilized ZrO₂ (ScYSZ) powder was synthesized by chemical co-precipitation method. The phase stability, sintering resistance and thermo-physical properties of ScYSZ and 8 wt%Y₂O₃ stabilized ZrO₂ (8YSZ) were investigated. The results indicated that both ScYSZ and 8YSZ show single tetragonal phase before heat treatment. After heat treating at 1500 °C for 300 h, ScYSZ exhibits excellent phase stability with 100% metastable tetragonal (t′) phase, whereas the content of monoclinic phase in 8YSZ reached 49.4 mol%. ScYSZ also exhibits higher sintering resistance and lower thermal conductivity than 8YSZ. ScYSZ can be considered to be explored as candidate material for TBC application.