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1.
The morphotropic composition of the lead-free solid solution between Na0.5Bi0.5TiO3 and BaTiO3 (0.94 Na0.5Bi0.5TiO3-0.06 BaTiO3 or NBT-6BT) is of particular interest for the next generation of high-temperature capacitors but remains plagued by the diversity of dielectric properties reported in the literature. In order to explain the apparent inconsistencies among the reported dielectric properties of NBT-6BT, we examine the influence of stoichiometry, phase separation, and metallization method. We show that the nominal stoichiometry has a crucial effect, since increasing the nominal Na/Bi ratio increases conductivity and dielectric losses (tan δ). It also increases the real part of the permittivity (ε’) and the frequency dispersion of both ε’ and tan δ, thereby altering the shape of the evolution with temperature of the dielectric properties. Moreover it increases the depolarization temperature (Td) and decreases the temperature of maximum permittivity (Tm). Phase separation also occurs during the synthesis of NBT-6BT as Na evaporation leads to the formation of secondary Ba-containing phases. We report that these phases can have a positive impact on the dielectric properties: a moderate volume fraction (2.5 to 3.0%) and average grain surface (0.9 to 3.0 µm2) of these secondary Ba-containing phases increase the relative permittivity, decrease the dielectric losses, and increase the insulation resistance. We also show that the metallization method impacts the dielectric properties and therefore may contribute to the differences between various reports. The dielectric properties of NBT-6BT samples are measured during successive heating/cooling cycles and reveal that the permittivity value is lower during the first heating when silver paste, even cured, is used. These three components contribute to explaining the diversity of the reported dielectric properties of NBT-6BT.  相似文献   
2.
With the development of advanced electrical and electronic devices and the requirement of environmental protection, lead-free dielectric capacitors with excellent energy storage performance have aroused great attention. However, it is a great challenge to achieve both large energy storage density and high efficiency simultaneously in dielectric capacitors. This work investigates the energy storage performance of sol-gel-processed (K,Na)NbO3-based lead-free ferroelectric films on silicon substrates with compositions of 0.95(K0.49Na0.49Li0.02)(Nb0.8Ta0.2)O3-0.05CaZrO3-x mol% Mn (KNN-LT-CZ5-x mol% Mn). The appropriate amount of Mn-doping facilitates the coexistence of orthorhombic and tetragonal phases, suppresses the leakage current, and considerably enhances the breakdown strengths of KNN-LT-CZ5 films. Consequently, large recoverable energy storage density up to 64.6 J cm−3 with a high efficiency of 84.6% under an electric field of 3080 kV cm−1 are achieved in KNN-LT-CZ5-5 mol% Mn film. This, to the best of our knowledge, is superior to the majority of both the lead-based and lead-free films on silicon substrates and thus demonstrates great potentials of (K,Na)NbO3-based lead-free films as dielectric energy storage materials.  相似文献   
3.
The structure and properties of Mn-doped 0.67BiFeO3-0.33BaTiO3 ceramics are systematically investigated with respect to the effects of annealing prior to rapid cooling by quenching in air. Air-quenching induces a change in crystal structure from pseudo-cubic to rhombohedral, with higher quenching temperatures leading to an increased rhombohedral distortion. These structural changes are correlated with the appearance of more well-defined ferroelectric domain configurations. It is shown that the surface preparation procedures for XRD measurements can induce significant changes in the peak profiles, indicating differences in crystal structure between the surface and bulk regions. Frequency dispersion in the temperature-dependent relative permittivity for the as-sintered sample is significantly reduced after quenching, accompanied by enhancement of the Curie point and improved temperature-stability of piezoelectric properties. It is proposed that the formation of defect clusters by A-site cation diffusion during cooling is circumvented by quenching, leading to the observed modification of structural distortion and ferroelectric properties.  相似文献   
4.
在Zn20Sn高温无铅钎料合金中添加0.1%RE及0.2%~0.8%Ni(质量分数,下同),研究了RE及Ni对钎料合金显微组织及性能的影响。结果表明,在Zn20Sn中同时添加0.1%RE及0.2%~0.8%Ni后,钎料合金的固相线变化不大,而液相线温度降低;RE及Ni对钎料合金的润湿性能及显微硬度有明显的影响,当RE为0.1%、Ni为0.4%时,钎料合金的润湿性能最好、显微硬度最高;随着RE及Ni的添加,在钎料合金中形成了含Ni金属间化合物,且随着Ni含量的提高,金属间化合物的形状、钎料合金的组织结构发生显著变化。  相似文献   
5.
以钙系生料釉为基础,引入结晶剂CuO、MnO2制备无铅CuO-MnO2系金属光泽釉;结合XRD、SEM-EDS进行物相组成定性分析和显微结构表征,系统探究外加TiO2、V2O5以及玻璃粉对金属光泽釉釉面分相的影响。研究表明:一定量的TiO2、V2O5引入能有效促进釉面的分相,将玻璃粉部分替换基础釉中的钾长石能使得釉熔体的高温粘度降低,并进一步加剧釉面分相,促进CuMn2O4铜锰尖晶石在釉层表面的析出和富集;当TiO2引入量为2%,V2O5引入量为1%,玻璃粉引入量为25%(同为质量分数)时,金属光泽釉釉面效果最佳。  相似文献   
6.
0.75(Na0.5Bi0.5)TiO3–0.25SrTiO3 lead-free incipient piezoceramic is a promising candidate for actuator applications due to their large reversible electromechanical strains at the relatively low driving field of 40 kV/cm. In order to further reduce the driving field of 0.75(Na0.5Bi0.5)TiO–0.25SrTiO3 relaxor ceramic to meet the requirements for real actuators application, the relaxor/ferroelectric (RE/FE) 0-3 composite ceramics method was employed. The polarization and strain behaviors were examined as a function of the weight ratio of the relaxor/ferroelectric phases. It was found that 90 wt% 0.75(Na0.5Bi0.5)TiO3–0.25SrTiO3/10 wt% 0.96(Na0.84K0.16)1/2Bi1/2TiO3–0.04SrTiO3 RE/FE 0-3 type composite samples provided a high unipolar strain of 0.25% and the corresponding large-signal piezoelectric coefficient, d*33 of 833 pm/V at 30 kV/cm, which are 32% higher than the values of the pure 0.75(Na0.5Bi0.5)TiO3–0.25SrTiO3. The enhanced electric-field-induced strain at relatively lower field was attributed primarily to the reduction in the RE-FE phase transition electric field. It was also found that the RE/FE composite ceramics exhibited significantly reduced frequency dependence in the unipolar strain behavior at room temperature.  相似文献   
7.
研究了铜基板退火处理对Cu/Sn58Bi界面微结构的影响.结果表明,在回流以及时效24 h后Cu/Sn58Bi/Cu界面只观察到Cu6Sn5.随着时效时间的增加,在界面形成了Cu6Sn5和Cu3Sn的双金属间化合物(IMC)层,并且IMC层厚度也随之增加.长时间时效过程中,在未退火处理的铜基板界面产生了较多铋偏析,而在退火处理的铜基板界面较少产生铋偏析.比较退火处理以及未退火处理的铜基板与钎料界面IMC层生长速率常数,发现铜基板退火处理能减缓IMC层生长,主要归因于对铜基板进行退火处理能够有效的消除铜基板的内应力与组织缺陷,从而减缓Cu原子的扩散,起到减缓IMC生长的作用.  相似文献   
8.
Ba(Ti1-xHfx)O3 ceramics were synthesized by a solid-state reaction process. The evolution of the phase structure was identified by XRD spectrum, dielectric spectroscopy, and temperature-dependent Raman spectroscopy for the Ba(Ti1-xHfx)O3 ceramics. In addition, pyroelectric energy harvesting properties based on the Olsen cycle were investigated for the first time. A maximum pyroelectric energy harvesting density value of ND = 491.30 kJ/m3= 120°C, EH = 50 kV/cm) was achieved in the Ba(Hf0.05Ti0.95)O3 ceramic. Compared with those of BT, the values of ND more than doubled in the temperature range from Δ= 60°C to Δ= 100°C in the Ba(Hf0.05Ti0.95)O3 ceramic and even increased 3.2 times at Δ= 80°C near the Curie temperature (TC) of the Ba(Hf0.05Ti0.95)O3 sample. In addition, a larger pyroelectric energy harvesting density value of ND = 367.10 kJ/m3= 120°C, EH = 50 kV/cm) was acquired in the Ba(Hf0.12Ti0.88)O3 ceramic. Values of ND-BHT5/ND-BT and ND-BHT12/ND-BT were analyzed in the Ba(Ti1-xHfx)O3 ceramics. The optimal pyroelectric properties can be obtained in the vicinity of the ferroelectric to paraelectric phase-transition region.  相似文献   
9.
Nitrogen-doped BaTiO3 (BT) ceramics were produced by the solid-state reaction method in conjunction with ammonia gas treatment. The optical absorption spectra results show that the bandgap of BT ceramic is narrowed after N-doping, suggesting that the N-doping is an effective route to increase light absorption. Polar properties measurements indicate that the ferroelectricity of BT ceramic is well maintained after the N-doping. In addition, the electric-field–induced strain is prominently improved to ~0.8% after N-doping, a value superior to that of PZT. Furthermore, the influence of N-doping on photoelectric properties of BT ceramics was also investigated. Large increase in photoconductivity and fast response to light illumination conditions were observed in N-doped BT ceramics. This work provides a novel route to enhance the (photo)electric properties of ferroelectric materials.  相似文献   
10.
Recently, lead-free piezoelectric thin films have received increasing attention due to the growing demands for mircoelectromechanical systems and the significant progress in lead-free piezoelectric research. Here, potassium sodium niobate [(K, Na)NbO3 (KNN)]-based thin films were fabricated via a sol-gel method. The effects of pyrolysis temperature on the resulting microstructure and electrical properties of KNN-based films were investigated. The KNN-based film pyrolyzed at 550°C and annealed at 700°C shows a dominant (100) orientation with a high texturing degree of 91.7%. The microstructures, morphologies, piezo- and ferroelectric properties of the KNN-based films were discussed in association with different pyrolysis temperatures. The crystallization mechanism of the (100) textured KNN-based thin films was elaborated in detail.  相似文献   
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