Dielectric Relaxation in CaO–Bi2O3–B2O3 Glasses

Glasses in the system CaO–Bi₂O₃–B₂O₃ (in molar ratio) have been prepared using melt-quenching route. Ion transport characteristics were investigated for this glass using electric modulus, ac conductivity and impedance measurements. The ac conductivity was rationalized using Almond–West power law. Dielectric relaxation has been analyzed based on the behavior of electric modulus behavior. The activation energy associated with the electrical relaxation determined from the electric modulus spectra was found to be 1.76 eV, close to that the activation energy for dc conductivity (1.71 eV) indicating that the same species took part in both the processes. The stretched exponent β (0.5–0.6) is invariant with temperature for the present glasses.     

Near Constant Loss Dielectric Response in 2Bi2O3–B2O3 Glasses

Electrical conduction and relaxation phenomena in bismuth borate glasses in the composition 2Bi₂O₃–B₂O₃ (Bi₄B₂O₉) were investigated. Dielectric studies carried out on these glasses revealed near constant loss response in the 1 kHz–1 MHz frequency range at moderately high temperatures (300–450 K) associated with relatively low loss (tan δ = 0.006) and high dielectric constant (ε_r′ = 37) at 1 kHz, 300 K. The variation in AC conductivity with temperature at different frequencies showed a cross over from near constant loss response characterized by local ion vibration within the potential well to universal Jonscher's power law dependence triggered by ion hopping between potential wells or cages. Thermal activation energy for single potential well was found to be 0.48 ± 0.05 eV from cross over points. Ionic conduction and relaxation processes were rationalized by modulus formalism. The promising dielectric properties (relatively high ε_r′ and low tan δ) of the present glasses were attributed to high density (93% of its crystalline counterpart), high polarizability, and low mobility associated with heavy metal cations, Bi³⁺.     

Viscous behaviour of Bi2O3–B2O3–ZnO glass composites with ceramic fillers

Abstract

Variation in the viscous flow behaviour, nature and extent of glass fluidity in glass/filler composites are addressed with respect to various factors such as filler type, content, size, density and migration distance. The characterisation of a glass (Bi₂O₃–B₂O₃–ZnO) composite consisting of two different fillers (cordierite and willemite) was determined using hot stage microscopy, a differential scanning calorimeter and a flow button test. The microstructure was analysed using a scanning electron microscope. The apparent viscosity of the glass composites increased on increasing concentration and density of the filler. The variation in the viscosity is due to the diffusion of the glass matrix through channels in the cordierite filler of the composite. Based on the calculated migration distance of the filler in the glass matrix, the present work suggests that the interfacial behaviour and the density of the filler play a significant role in determining the viscous flow of the glass composites.     

Network of Bi2O3–Al2O3–NaPO3 glasses studied by solid-state nuclear magnetic resonance spectroscopy

A detailed structural investigation of a series of phosphate laser glasses with composition xBi₂O₃–yAl₂O₃–(100 − x–y)NaPO₃ (x = 0, 10; y = 0, 5, 10, 15, 20) has been conducted using solid-state nuclear magnetic resonance (NMR) techniques and X-ray photoelectron spectroscopy (XPS). ³¹P MAS NMR spectroscopy demonstrates that the addition of Bi₂O₃ and Al₂O₃ leads to the depolymerization of the phosphorus chain in the process of Q² → Q¹ → Q⁰. The various phosphorus species (Qⁿ, n = 0, 1, 2) are identified by ³¹P single pulse, ³¹P{²⁷Al} rotational echo adiabatic passage double resonance, ³¹P{²⁷Al} J-coupling-based heteronuclear multiple-quantum coherence, and 1D refocused INADEQUATE experiments. The results of ²³Na{³¹P}, ³¹P{²³Na}, ²⁷Al{³¹P} rotational echo double resonance, and XPS consistently confirm that Na⁺, Al³⁺, and Bi³⁺ ions are all bound by phosphorus tetrahedron [PO₄]³⁻. No bond is formed between these glass modifiers. Based on the complementary evidence from previous experiments, comprehensive local structure models are developed for these Bi₂O₃–Al₂O₃–NaPO₃ glasses.     

Experimental determination of the liquidus line in the high Bi2O3 region in the TiO2–Bi2O3 system

Liquidus line in the high-Bi₂O₃-containing region of the TiO₂–Bi₂O₃ system was determined experimentally. The equilibrating and quenching technique with subsequent electron probe microanalyser (SEM-EDS) microanalysis were employed. Based on the data, liquidus line was constructed between 60 and 92 mol% Bi₂O₃. The current results showed a higher solubility of Bi₂O₃ in the liquid phase in equilibrium with the Bi₄Ti₃O₁₂ compound compared with the existing phase diagram. In addition, differential scanning calorimetry (DSC) was used to estimate the transformations covering the composition range from 60 to 95 mol% Bi₂O₃. Further, the phase diagram of the TiO₂–Bi₂O₃ system was calculated using a quasichemical model for the liquid phase. The thermodynamic properties of the intermediate compounds were estimated from the data of TiO₂ and Bi₂O₃ pure solids.     

Effect of Sb_2O_3 Replace V_2O_5 on the Electronic Property of V2O5–P2O5–Sb2O3–Bi2O3 Glass System

采用体积电阻率法、红外光谱、X射线衍射研究了V2O5–P2O5–Sb2O3–Bi2O3体系玻璃的电性能、结构和析晶状况。结果表明：随着Sb2O3取代部分V2O5,玻璃的体积电阻率显著升高,电子分别以V4＋和V5＋为中心不停地进行电子跃迁的电子导电特征得到明显抑制,15%Sb2O3、20%Sb2O3玻璃的体积电阻率可以达到实用水平。当Sb2O3取代V2O5进入钒酸盐玻璃中,玻璃结构得到增强,析晶状况得到改善,削弱了玻璃的导电能力。     

Bi2O3-B2O3-SiO2玻璃的热性质

研究了Bi2O3-B2O3-SiO2系玻璃的成玻性能、转变温度(Tg)和热膨胀系数(CTE)，确定了该系统易熔封接玻璃的玻化范围以及玻璃的转变温度和玻璃的热膨胀系数与玻璃组成的关系。     

Dielectric behaviors of Nb2O5–Co2O3 doped BaTiO3–Bi(Mg1/2Ti1/2)O3 ceramics

Nb₂O₅ and Nb–Co doped 0.85BaTiO₃–0.15Bi(Mg_1/2Ti_1/2)O₃ (0.85BT–0.15BMT) ceramics were investigated. From XRD patterns, undesired phase was observed when the (Nb₂O₅/Nb-Co) doping levels exceed 3 wt.%/2 wt.%, giving rise to the deteriorate dielectric constant. The 0.85BT–0.15BMT ceramics doped with 2 wt.%Nb₂O₅ was found to possess a moderate dielectric constant (? ～ 1000) and low dielectric loss (tan δ = 0.9%) at room temperature and 1 kHz, showing flat dielectric behavior over the temperature range from ?55 to 155 °C. It was found that the formation of core–shell structure in the BT based ceramics is controlled by the doping sequence of Nb- and Bi-oxides.     

Microstructure and electrical properties of ZnO–ZrO2–Bi2O3–M3O4 (MCo,Mn) varistors

Phase evolution, microstructure and the electrical properties of ZrO₂-added pyrochlore-free ZnO–Bi₂O₃–M₃O₄ (MCo, Mn) varistors have been studied as functions of ZrO₂ content up to 10 vol% and the sintering temperature between 900 and 1300 °C. Zirconia remained as intergranular second phase particles up to 1100 °C, which retarded densification and inhibited the grain growth of ZnO. At higher temperatures, on the contrary, ZrO₂ particles began to be entrapped in ZnO grains and irreversibly transform from monoclinic to stable cubic phase dissolving transition metal ions. The grain size of ZnO decreased with increasing ZrO₂ content, and increased with the increase of the sintering temperature. Accordingly breakdown voltage changed with both ZrO₂ content and the sintering temperature as was expected. Nonlinear coefficient (α) depended primarily on the sintering temperature: it increased to >40 up to 1000 °C, and significantly decreased to <30 at higher temperatures probably due to the volatilization of Bi₂O₃. While the specimens sintered at 1200 °C or above had relatively high leakage current (I_L) and large clamping ratio (C_R), those with ZrO₂ content of 0.5–5.0 vol% and sintered below 1200 °C revealed low I_L of ⩽20 μA/cm² and C_R well below 2.0. In spite that varistor characteristics of ZrO₂-added system could not match those of commercial ZnO varistors, its low temperature sinterability and ease of breakdown voltage control via ZrO₂ content without a serious loss of its figures of merit are worth noticing, particularly for multi-layered chip varistor (MLV) application.     

Effect of a Bi–Cr–O synthetic multi-phase on the microstructure and electrical properties of ZnO–Bi2O3 varistor ceramics

ZnO–Bi₂O₃–MnO₂ (ZBM)-based varistors were fabricated via doping a novel synthetic multi-phase (SMP) additive produced by calcining the mixture of 18Bi₂O₃·Cr₂O₃ at a given temperature. The effects of the SMP on the microstructural and electrical properties of ZBM varistors were investigated. It was found that the SMP dopant was a compound crystalline phases including Bi–Cr–O phases (Bi_7.38Cr_0.62O_12+x and CrBi₁₈O₃₀) and small amounts of Bi₂O₃ rather than a synthesized polycrystal. The Bi–Cr–O phases were not emerged for samples with x=1, indicating that the amount of it is tiny and the small Bi₂O₃ may accelerate ZnO grain growth. With more SMP doping (x>1) in the ZBM ceramics, it acted as a barrier inhibiting grain growth. For samples with x=5, excellent electrical properties were obtained: the nonlinear coefficient α increased up to 50.19 corresponding to the highly barrier height of 2.62 eV; the leakage current I_L reduced to 0.3 μA. The dielectric constant ε_a is proportional to the ratio of the grain size d to the thickness of the depletion layer width t, which explained the ε_a increased at f=1 kHz for the samples with x=1 and 5. The improvement of the electrical properties can be explained by the oxygen absorption mechanism.     

Nanocrystalline Bi2O3–B2O3– (MoO3 or V2O5) glass-ceramic systems for organic pollutants degradation

Fixation of photocatalyst in glass matrix would solve the problem of photocatalyst recovery. In this study, the system 30 Bi₂O₃, 20 B₂O₃ and 50 (MoO₃ or V₂O₅), was used for the preparation and stabilization of the photoactive phases of both bismuth molybdate β-Bi₂Mo₂O₉ and monoclinic–scheelite BiVO₄ in a glassy matrix. Proper heat-treatment schedule, based on differential thermal analysis (DTA) results, has been applied to improve the crystallinity of the prepared glass–ceramics. The applied heat-treatment program showed a significant effect on the size of the formed crystals, especially in samples with molybdenum content. For instance, one-step heat-treatment (500°C/2 h) improves the crystallinity of the material than two-step heat-treatment (355°C/1 h+400°C/2 h). It was also noticed that the amount of glassy matrix relative to crystalline part in case of vanadium-contained samples is much more than that in the corresponding molybdenum-contained samples. The prepared samples were used for the degradation of Red SPD Cotton dye in order to assess their photocatalytic activity. All molybdenum contained samples showed a promising photocatalytic activity. On contrary, vanadium-contained samples were inactive suggesting that most of photoactive crystals are in the bulk of materials.     

The characteristics of ZnO–Bi2O3-based varistor ceramics doped with Y2O3 and varying amounts of Sb2O3

ZnO–Bi₂O₃-based varistor samples doped with 0.45 mol% of Y₂O₃ and varying amounts of Sb₂O₃ in the range from 1.8 to 0.0 mol% were fired at 1230 °C. Only in the samples co-doped with Sb₂O₃ did doping with Y₂O₃ resulted in the formation of a fine-grained Bi–Zn–Sb–Y–O phase (the Y₂O₃-containing phase) at the grain boundaries, which very effectively hinders the grain growth. Despite of a decrease in the amount of added Sb₂O₃ from 1.8 to 0.45 mol% and a significant decrease in the amount of spinel phase the samples had a similar ZnO grain size and a threshold voltage of 200 V/mm. The results confirmed that doping with Y₂O₃ is a very promising route for the production of fine-grained high-voltage ZnO–Bi₂O₃-based varistor ceramics, and determining the proper amounts of added Sb₂O₃ and Y₂O₃ is of great importance.     

Bi2O3-B2O3-Ga2O3玻璃的光学折射率和带隙研究

采用传统熔融淬冷法制备了5组高Bi2O3含量的Bi2O3-B2O3-Ga2O3系统玻璃样品.测试了玻璃样品的密度,折射率和吸收光谱.利用经典的Tauc方程计算了样品的间接允许光学带隙Eopgi,直接允许光学带隙Eopgd和Urbach能量ΔE.根据Duffy等人提出的经验推导公式计算了样品的能量带隙Eg.研究了Ga2O3含量对玻璃样品的密度、折射率、摩尔折射度Rm、金属标准值Mm、光学带隙、能量带隙和Urbach能量的影响,并分析了它们之间的关系.结果表明:随着Ga2O3含量的增加,玻璃样品的密度和折射率逐渐增大,但Ga3+对玻璃折射率的影响要小于B3+;玻璃样品的紫外吸收增强,光学带隙和能量带隙逐渐减小,光学带隙和能量带隙的比值约为1:1.1;Urbach能量逐渐减小,即玻璃中带裂变和缺陷形成的趋势越小.     

Bi2O3-SiO2系统高温熔体研究进展

Bi2O3-SiO2系统是一类重要的无机硅酸盐系统,其晶体材料具有光学、光电、电导、声光、压电等性能.本文综述了目前对于Bi2O3-SiO2系统高温熔体的认识,分析了Bi2O3-SiO2系统高温熔体的粘度突变、液相状态及熔体结构,最后阐明了该领域研究热点、可能的应用以及需要进一步研究开发的课题.     

Microstructure and characterization of interfacial phases of sapphire/sapphire joint bonded using Bi2O3–B2O3–ZnO glass

Bismuth borate zinc glass, 50Bi₂O₃–30B₂O₃–20ZnO (mol.%), was used as a braze intended to join sapphire. Thermal properties of the glass were all experimentally determined. The wettability of the glass on sapphire was investigated. The contact angle not greater than 11.3° was obtained in air at temperatures of ≥700 °C. Subsequently, sapphire was successfully joined to themselves at 700 °C for 20 min. The microstructure of the joint was studied and the interfacial phases were characterized. The results showed that the ZnAl₂O₄ phase was formed as a result of the reaction between the sapphire substrate and ZnO from the glass. The mechanical integrity of the joints was investigated. The joints with an average room shear strength of 70 MPa were achieved. The fracture analysis indicated that the fracture occurred within the glass interlayer rather than at the sapphire/glass interface, hence indicating a good bonding of the glass with sapphire.     

Bi2O3–AlPO4–SiO2溶胶–凝胶玻璃的制备及固体核磁共振结构解析

针对铋掺杂玻璃发光机理不明确的问题,以Bi2O3–AlPO4–SiO2玻璃为研究对象,对其开展结构研究.采用硝酸铋、乳酸铝、磷酸三乙酯和正硅酸四乙酯作为前驱体,通过溶胶–凝胶法制备了xBi2O3–AlPO4–SiO2(0≤x≤0.15)的三元体系玻璃,并使用固态核磁共振(NMR)技术及X射线光电子能谱系统解析了xBi2...     

Bi2O3-CaO-ZnO-Nb2O5系陶瓷介电性能研究

借助XRD,SEM,HP4140B微电流计和HP4274A阻抗分析仪等测试手段,研究实验制备的BCZN[(Bi1.5Ca0.5)(Zn0.5Nb1.5)O7]陶瓷试样介电性能,并第一次提出了介电常数临界温度和介质损耗临界温度的概念。结果表明:BCZN陶瓷是高频稳定形陶瓷,具有面心立方焦绿石结构,且在最佳烧结温度和保温时间下,为均一的α相单相结构;在很宽的频率范围内,介电常数较高(εr≈81)且很稳定,介质损耗很小(tanδ≈-1.0×10-4);它的介电常数在温度低于介电常数临界温度时,与温度呈线性关系,在温度高于介电常数临界温度时,发生高温突变;介质损耗在温度低于介质损耗临界温度时几乎不变,在温度高于介质损耗临界温度时,发生高温突变;介电常数临界温度和介质损耗临界温度都随频率的升高而升高。