Er2O3 Doping Effect on Varistor Properties and Multiimpulse Stress Behavior of ZnO–PrO1.83–CoO–Cr2O3–Dy2O3 Ceramics

The Er₂O₃ doping effects on varistor properties and impulse aging behavior of the ZnO–PrO_1.83–CoO–Cr₂O₃–Dy₂O₃ ceramics were investigated in the range of 0–2.0 mol%. The nonlinear coefficient increased from 42 to 56 with an increase in the amount of Er₂O₃. The clamp voltage ratio (K) decreased with an increase in the amount of Er₂O₃. The varistors doped with 2.0 mol% in the amount of Er₂O₃ exhibited the best clamping characteristics, with K = 1.43–1.83 at an impulse current of 1–50 A. The varistors doped with 0.25 mol% in the amount of Er₂O₃ exhibited the strongest electrical stability, with the variation rate of the breakdown field of ?0.5%, the variation rate of the nonlinear coefficient of ?5.5%, and the variation rate of the leakage current of ?1.5% after applying 400 times at an impulse current of 400 A     

掺杂Fe2O3对氧化锌压敏陶瓷压敏特性的影响

本文研究了分别掺杂微量Fe2O3杂质对ZnO压敏陶瓷的压敏特性的影响。研究结果表明:随Fe2O3掺杂量的增加,ZnO压敏陶瓷的压敏电压V1 mA和非线性系数先下降,后升高,最小值出现在Fe2O3摩尔掺杂量为1.00%;并从理论上详细地探讨了产生这些影响的原因。     

Temperature‐Stable Relative Permittivity from −70°C to 500°C in (Ba0.8Ca0.2)TiO3–Bi(Mg0.5Ti0.5)O3–NaNbO3 Ceramics

Temperature‐stable relaxor dielectrics have been developed in the solid solution system: 0.45Ba_0.8Ca_0.2TiO₃–(0.55 ? x)Bi(Mg_0.5Ti_0.5)O₃–xNaNbO₃. Ceramics of composition x = 0 have a relative permittivity ?_r = 950 ± 15% over a wide temperature range from +70°C to 600°C. Modification with NaNbO₃ at x = 0.2 decreases the lower limiting temperature to ?70°C, but also decreases relative permittivity such that ?_r ~ 600 ± 15% over the temperature range ?70°C to 500°C. For composition x = 0.3, the low‐temperature dispersion in loss tangent, tan δ, (at 1 kHz) shifts to lower temperature, giving tan δ values ≤0.02 across the temperature range ?60°C to 300°C in combination with ?_r ~ 550 ± 15%. Values of dc resistivity for all samples are of the order of 10¹⁰ Ω m at 250°C and 10⁷ Ω m at 400°C.     

The effect of SiO2 on electrical properties of low‐temperature‐sintered ZnO–Bi2O3–TiO2–Co2O3–MnO2‐based ceramics

ZnO–Bi₂O₃–TiO₂–Co₂O₃–MnO₂‐based (ZBTCM) varistors were fabricated via the conventional solid‐state method, and the effect of SiO₂ content on the phase transformation, microstructure, and electrical properties of the ZBTCM had been investigated. Results showed that this varistor can be sintered at a low temperature of 880°C with a high sintering density above 0.95 of the ZnO theoretical density. In these components, SiO₂ acts as a controller in ZnO grain growth, decreasing the grain size of ZnO from 3.67 to 1.92 μm, which in turn results in an increase in breakdown voltage E_1mA from 358.11 to 1080 V/mm. On the other hand, SiO₂ has a significant influence on the defect structure and component distribution at grain‐boundary regions. When SiO₂ content increases from 0 to 4 wt%, the value of the interface state density (N_s) increases sharply. At the same time, the electrical properties are improved gradually, and reach an optimized value with the nonlinear coefficient (α) up to 54.18, the barrier height (?_b) up to 2.90 eV, and the leakage current (I_L) down to 0.193 μA/cm².     

Perovskite‐Structured BiFeO3–Bi(Zn1/2Ti1/2)O3–PbTiO3 Solid Solution Piezoelectric Ceramics with Curie Temperature About 700°C

In this article, perovskite‐structured BiFeO₃–Bi(Zn_1/2Ti_1/2)O₃–PbTiO₃ (BF–BZT–PT) ternary solid solutions were prepared with traditional solid‐state reaction method and demonstrated to exhibit a coexistent phase boundary (CPB) with Curie temperature of T_C~700°C in the form of ceramics with microstructure grain size of several micron. It was found that those CPB ceramics fabricated with conventional electroceramic processing are mechanically and electrically robust and can be poled to set a high piezoelectricity for the ceramics prepared with multiple calcinations and sintering temperature around 750°C. A high piezoelectric property of T_C = 560°C, d₃₃ = 30 pC/N, ε₃₃^T/ε₀ = 302, and tanδ = 0.02 was obtained here for the CPB 0.53BF–0.15BZT–0.32PT ceramics with average grain size of about 0.3 μm. Primary experimental investigations found that the enhanced piezoelectric response and reduced ferroelectric Curie temperature are closely associated with the small grain size of microstructure feature, which induces lattice structural changes of increased amount ratio of rhombohedral‐to‐tetragonal phase accompanying with decreased tetragonality in the CPB ceramics. Taking advantage of structural phase boundary feature like the Pb(Zr,Ti)O₃ systems, through adjusting composition and microstructure grain size, the CPB BF–BZT–PT ceramics is a potential candidate to exhibit better piezoelectric properties than the commercial K‐15 Aurivillius‐type bismuth titanate ceramics. Our essay is anticipated to excite new designs of high–temperature, high–performance, perovskite‐structured, ferroelectric piezoceramics and extend their application fields of piezoelectric transducers.     

Formation of Bi2ZnB2O7 Nanocrystals in ZnO–Bi2O3–B2O3 Glass Induced by Femtosecond Laser

We report on the formation of Bi₂ZnB₂O₇ crystal structures with designated patterns in ZnO–Bi₂O₃–B₂O₃ glass by femtosecond laser direct writing. The crystallization mechanism in glass is investigated by crystallization kinetics analysis and simulation of the three‐dimensional temperature field distribution. The crystallized regions show larger third‐order optical nonlinearity than the unirradiated region in glass by Z‐scan technique. This finding is of great potential in application of nonlinear optical integrated devices and development of new nonlinear materials.     

Aerosol Codeposition of Ceramics: Mixtures of Bi2O3–TiO2 and Bi2O3–V2O5

Aerosol deposition (AD) is a promising method to apply ceramic films on a wide range of substrate materials. Until now, AD has mainly been performed using a single ceramic powder. In this work, mixtures of two different ceramic powders were prepared. The first mixture consisted of Bi₂O₃ and TiO₂ and the second consisted of Bi₂O₃ and V₂O₅, in stoichiometric ratios to form Bi₄Ti₃O₁₂ and Bi₄V₂O_11?δ, respectively. Aerosol codeposition produced films with homogeneously distributed particle fractions and thicknesses between 10 and 100 μm. Composite films were annealed to temperatures up to 750°C to enable an in situ calcination and attempted formation of the above‐mentioned compounds. Successful formation of Bi₄Ti₃O₁₂ was tracked by hot‐stage X‐ray diffraction (XRD), and confirmed by dielectric measurements. Formation of the intended Bi₄V₂O_11?δ, on the other hand, was not achieved, but rather BiVO₄, which was confirmed by XRD, EDX and electrical measurements. The bismuth deficiency occurred during spray deposition, and is attributed to powder/material characteristics. Additional insight about the AD process is gained by comparing mixtures of oxides with different relative hardness values. Aerosol codeposition of ceramics may be an interesting new technique for producing porous functional ceramics.     

Influence of Crystallization on the Conversion of Sm3+→Sm2+ in SrO–Bi2O3–K2O–B2O3 Glass‐Ceramics

Sm³⁺‐doped glass 13SrO–2Bi₂O₃–5K₂O–80B₂O₃ was fabricated by the conventional melt‐quenching technique. The glass‐ceramics were obtained by heating the as‐prepared glasses in air atmosphere at selected temperatures 550°C, 600°C, 615°C, and 650°C, respectively. The luminescence spectra of both Sm³⁺ and Sm²⁺ were detected in the ceramic heated at 650°C where crystalline phase is formed. The as‐prepared glass and the ceramics heated at 550°C, 600°C, and 615°C show only the emission due to Sm³⁺. In the sample heated at 650°C in air atmosphere, however, part of Sm³⁺ ions was converted to Sm²⁺, giving rise to sharp emission lines which are characteristic of Sm²⁺ in crystalline state. It is suggested that Sm²⁺ ions are located at Sr²⁺ site in the ceramic while Sm³⁺ ions are located at Bi³⁺ sites. The Sm²⁺‐doped glass‐ceramic has a high optical stability because the fluorescence intensity decreases by only about 8% of its initial value upon excitation at 488 nm Ar⁺ laser.     

Microstructures and Microwave Dielectric Properties of Bi2O3‐Deficient Bi12SiO20 Ceramics

The Microstructure and microwave dielectric properties of Bi₂O₃‐deficient Bi₁₂SiO₂₀ ceramics were investigated. A small amount of unreacted Bi₂O₃ phase melted during sintering at 825°C and assisted with densification and grain growth in all samples. The melted Bi₂O₃ reacted with remnant SiO₂ during cooling to form a Bi₄Si₃O₁₂ secondary phase. The nominal composition of Bi_11.8SiO_19.7 ceramics sintered at 825°C for 4 h had a high relative density of 97% of the theoretical density, and good microwave dielectric properties: ε_r = 39, Q × f = 74 000 GHz, and τ_f = ?14.1 ppm/°C. Moreover, this ceramic did not react with Ag at 825°C.     

Nd2O3掺杂对BCZT陶瓷结构及介电性能的影响

采用固相反应法制备Ba0.92-xCa0.08Ndx(Zr0.18Ti0.815Y0.0025Mn0.0025)O3(BCZT-Nd,x=0、0.005、0.010、0.020)陶瓷,研究了Nd2O3掺杂对Ba0.92Ca0.08(Zr0.18Ti0.82)O3(BCZT)陶瓷结构及介电性能的影响。结果表明,不同含量Nd3+作为施主掺杂离子进入A位和含量均为0.25%(摩尔分数)的Mn2+和Y3+作为受主掺杂进入B位均能提高BCZT陶瓷的致密性,细化晶粒作用明显,所有样品均为单一的四方BaTiO3相结构。随Nd2O3掺杂量增加,BCZT-Nd陶瓷介电峰值温度Tm向低温方向移动,相变弥散程度增强,Nd3+含量≥0.005mol时即表现出明显的弛豫铁电体特征。     

Microstructure and Electrical Properties of Nonstoichiometric 0.94(Na0.5Bi0.5+x)TiO3–0.06BaTiO3 Lead‐Free Ceramics

0.94(Na_0.5Bi_0.5+x)TiO₃–0.06BaTiO₃ (x = ?0.04, 0, 0.02; named NB_0.46T‐6BT, NB_0.50T‐6BT, NB_0.52T‐6BT, respectively) lead‐free piezoelectric ceramics were prepared via the solid‐state reaction method. Effects of Bi³⁺ nonstoichiometry on microstructure, dielectric, ferroelectric, and piezoelectric properties were studied. All ceramics show typical X‐ray diffraction peaks of ABO₃ perovskite structure. The lattice parameters increase with the increase in the Bi³⁺ content. The electron probe microanalysis demonstrates that the excess Bi₂O₃ in the starting composition can compensate the Bi₂O₃ loss induced during sample processing. The size and shape of grains are closely related to the Bi³⁺ content. For the unpoled NB_0.50T‐6BT and NB_0.52T‐6BT, there are two dielectric anomalies in the dielectric constant–temperature curves. The unpoled NB_0.46T‐6BT shows one dielectric anomaly accompanied by high dielectric constant and dielectric loss at low frequencies. After poling, a new dielectric anomaly appears around depolarization temperature (T_d) for all ceramics and the T_d values increase with the Bi³⁺ amount decreasing from excess to deficiency. The diffuse phase transition character was studied via the Curie–Weiss law and modified Curie–Weiss law. The activation energy values obtained via the impedance analysis are 0.69, 1.05, and 1.16 eV for NB_0.46T‐6BT, NB_0.50T‐6BT and NB_0.52T‐6BT, respectively, implying the change in oxygen vacancy concentration in the ceramics. The piezoelectric constant, polarization, and coercive field of the ceramics change with the variation in the Bi³⁺ content. The Rayleigh analysis suggests that the change in electrical properties of the ceramics with the variation in the Bi³⁺ amount is related to the effect of oxygen vacancies.     

Frequency and Temperature‐Independent Electrical Transport Properties of 2BaO–0.5Na2O–2.5Nb2O5–4.5B2O3 Glass‐Ceramics

The temperature (300–973 K) and frequency (100 Hz–10 MHz) response of the dielectric and impedance characteristics of 2BaO‐0.5Na₂O–2.5Nb₂O₅–4.5B₂O₃ glasses and glass nanocrystal composites were studied. The dielectric constant of the glass was found to be almost independent of frequency (100 Hz–10 MHz) and temperature (300–600 K). The temperature coefficient of dielectric constant was 8 ± 3 ppm/K in the 300–600 K temperature range. The relaxation and conduction phenomena were rationalized using modulus formalism and universal AC conductivity exponential power law, respectively. The observed relaxation behavior was found to be thermally activated. The complex impedance data were fitted using the least square method. Dispersion of Barium Sodium Niobate (BNN) phase at nanoscale in a glass matrix resulted in the formation of space charge around crystal‐glass interface, leading to a high value of effective dielectric constant especially for the samples heat‐treated at higher temperatures. The fabricated glass nanocrystal composites exhibited P versus E hysteresis loops at room temperature and the remnant polarization (P_r) increased with the increase in crystallite size.     

烧结温度对Bi2(Mg1/3Nb2/3)2O7介电陶瓷性能的影响

采用传统固相反应法制备了Bi2(Mg1/3Nb2/3)2O7(β-BMN)介电陶瓷,借助X射线衍射(XRD)研究了不同预烧温度合成β-BMN粉体的物相组成,借助扫描电镜(SEM)研究了不同烧结温度β-BMN的显微结构,考察了不同烧结温度和保温时间对β-BMN陶瓷性能的影响.结果表明:合成温度为850℃时已经完全形成主晶相(β-BMN).随着烧结温度的增加,样品的介质损耗(tanδ)先变小后增大,而相对介电常数(εr)先增大后减小.当烧结温度为1000℃保温5h时,得到的陶瓷的综合性能较佳:ρ=7.69g/cm3,εr=207,tanδ=0.00197.     

High‐temperature calorimetric study of oxide component dissolution in a CaO–MgO–Al2O3–SiO2 slag at 1450°C

Blast‐furnace slags are formed, as iron ore is reduced to metal, as a molten a mixture of refractory and not easily reducible oxides, largely silica, alumina, lime, and magnesia. Their relatively low silica content makes them basic and poor glass formers. Their thermodynamic properties, though important for modeling their formation and reactivity, as well as furnace heat balance, are poorly known. Solution calorimetry of small amounts of solid oxides in a molten oxide solvent at high temperature (up to about 1500°C) permits direct assessment of energetics of dissolution. The enthalpies of solution of slag forming oxides: CaO, SiO₂, Al₂O₃, MgO, and Fe₂O₃ in a simplified model slag of composition: CaO (45.9 mol%), SiO₂ (35.1 mol%), Al₂O₃ (8.3 mol%), MgO (10.7 mol%) were measured by high‐temperature drop solution calorimetry at 1450°C. For this slag composition, enthalpies of solution become more exothermic in the order: Fe₂O₃ (279.3 ± 20.8 kJ/mol), MgO (56.7 ± 9.1 kJ/mol), Al₂O, (41.6 ± 11.3 kJ/mol), CaO (?4.3 ± 2.3 kJ/mol), and SiO₂, (?20.4 ± 4.4 kJ/mol), reflecting the relatively basic character of this low‐silica melt. Within these fairly large experimental errors, characteristic of calorimetry at this high temperature, there is little or no discernible concentration dependence for these heats of solution. The trends seen for these five solutes parallel those seen for heats of solution of the same oxides in other melts at various temperatures, with changes in magnitude reflecting the differences in acid‐base character of the melts. The new data for quartz show systematic behavior which extends the range of basicity studied for the enthalpy of dissolution of silica. The results provide reliable data for future modeling of the thermal balance of steel‐making furnaces and geologic and ceramic systems.     

Subsolidus Phase Relationship in the CaO–CuO–TiO2 Ternary System at 950°C in Air

The subsolidus phase relationship in the CaO–CuO–TiO₂ ternary system at 950°C in air was investigated. Total 26 samples having various nominal compositions were prepared by the solid‐state reaction at 950°C in air, and their equilibrium phases were analyzed by powder X‐ray diffraction (XRD). The CaCu₃Ti₄O₁₂ phase exhibits variable stoichiometry and forms as the Ca_1?xCu_3+xTi₄O₁₂‐type (?0.019 ≤x ≤0.048) solid solution at 950°C in air. On the basis of our results and previous reports on the binary phase diagrams, the subsolidus phase diagram of the CaO–CuO–TiO₂ ternary system could be constructed at 950°C in air.     

High‐Temperature Oxidation of ZrB2–SiC–AlN Composites at 1600°C

The effect of AlN substitution on oxidation of ZrB₂–SiC was evaluated at 1600°C up to 5 h. Replacement of ZrB₂ by AlN, with 30 vol% SiC resulted in improved oxidation resistance with a thinner scale and reduced oxygen affected area. On the other hand, substitution of AlN for SiC resulted in a deterioration of the oxidation resistance with an abnormal scale and significant recession. The effect of SiC content was also studied, and was found to be consistent with the literature for the composites without AlN additions. A similar effect was observed when AlN was added, with the higher SiC content materials showing improved oxidation resistance. X‐ray photoelectron spectroscopy showed the presence of Al₂O₃ and SiO₂ on the surface, which could possibly lead to a modification in the viscosity of the glassy oxide scale. Possibly, the oxidation behavior of ZrB₂–SiC composites can be improved with controlled AlN additions by adjusting the Al:Si ratios.     

Core–Shell Structure and Dielectric Properties of Ba0.991Bi0.006TiO3@Nb2O5–Co3O4 Ceramics

To meet the needs of future multilayer ceramic capacitors (MLCCs), thinner dielectric layers are necessary. To achieve this goal, the grain size and uniformity of the particles must be effectively controlled. In this study, we confirmed a core–shell particle structure by means of X‐ray diffraction, scanning electron microscopy, and energy‐dispersive spectroscopy. The dielectric properties of the ceramics were measured using an LCR meter. We found Ba_0.991Bi_0.006TiO₃ particles form a core that was coated with a homogeneous Nb₂O₅–Co₃O₄ layer (~9 nm). The relationship between core–shell structure and ε_r‐T curves of the Ba_0.991Bi_0.006TiO₃@Nb₂O₅–Co₃O₄ ceramics by different sintering temperature has been investigated. Dense, fine‐grained Ba_0.991Bi_0.006TiO@Nb₂O₅–Co₃O₄ ceramics were obtained by sintering at 1160°C. The ceramics met the X8R requirements, with a maximum dielectric constant of 2795, and a low dielectric loss at room temperature of 0.89%.     

Microstructural and Microwave Dielectric Properties of Bi12GeO20 and Bi2O3‐Deficient Bi12GeO20 Ceramics

Bi₁₂GeO₂₀ ceramics sintered at 800°C had dense microstructures, with an average grain size of 1.5 μm, a relative permittivity (ε_r) of 36.97, temperature coefficient of resonance frequency (τ_f) of ?32.803 ppm/°C, and quality factor (Q × f) of 3137 GHz. The Bi_12‐xGeO_20‐1.5x ceramics were well sintered at both 800°C and 825°C, with average grain sizes exceeding 100 μm for x ≤ 1.0. However, the grain size decreased for x > 1.0 because of the Bi₄Ge₃O₁₂ secondary phase that formed at the grain boundaries. Bi_12‐xGeO_20‐1.5x (x ≤ 1.0) ceramics showed increased Q × f values of >10 000 GHz, although the ε_r and τ_f values were similar to those of Bi₁₂GeO₂₀ ceramics. The increased Q × f value resulted from the increased grain size. In particular, the Bi_11.6GeO_19.4 ceramic sintered at 825°C for 3 h showed good microwave dielectric properties of ε_r = 37.81, τ_f = ?33.839 ppm/°C, and Q × f = 14 455 GHz.     

A Comparison of 0°–0° and 45°–45° bridge‐Seeded,YBCO single grains

A variety of multiseeding techniques have been investigated over the past 20 yr in an attempt to enlarge bulk (RE)BCO superconducting samples fabricated by the top‐seeded melt growth (TSMG) process for practical applications. Unfortunately, these studies have failed to establish whether technically useful values of trapped field can be achieved in multiseeded bulk samples. In this work specially designed, 0°–0° and 45°–45° bridge seeds of different lengths have been employed to produce improved alignment of the seeds during the TSMG process. The ability of these bridge‐seeded samples to trap magnetic field, which is the key superconducting property for practical applications of bulk (RE)BCO, is compared for the samples seeded using 0°–0° and 45°–45° bridge seeds of different lengths. The grain boundaries produced by these bridge seeds are analyzed in detail, and the similarities and differences between the two bridge‐seeding processes are discussed.