Dielectric properties of Sb2O3-doped Ba0.672Sr0.32Y0.008TiO3

Sb₂O₃-doped Ba_0.672Sr_0.32Y_0.008TiO₃ (BSYT) dielectric ceramics were prepared by conventional solid state method, and their dielectric properties were investigated with variation of Sb₂O₃ doping content and sintering temperature. The X-ray diffraction patterns indicated that all the BSYT specimens possessed the perovskite polycrystalline structure. The experimental results reveal that the introduction of Sb₂O₃ into Ba_0.672Sr_0.32Y_0.008TiO₃ can control the grain growth, reduce the relative dielectric constant and dielectric loss, shift the Curie temperature to lower temperature and significantly improve the thermal stability of the BSYT ceramics. The samples doped with 1.6 wt.% Sb₂O₃ sintered at 1320 °C for 2 h exhibited attractive properties, including high relative dielectric constant (> 1500), low dielectric loss (< 40 × 10^− 4), low temperature coefficient of capacitor(< ± 35%) over a wide temperature range from − 25 °C to + 85 °C.     

PTCR properties of Sb2O3-doped (Ba,Sr)TiO3

Perovskite barium–strontium titanate, (Ba,Sr)TiO₃ was prepared and effects of Sb₂O₃ additives on its PTCR properties were investigated. The (Ba,Sr)TiO₃ with 0.05∼0.25 mol% Sb₂O₃ showed semiconducting PTCR behavior and anomalous grain growth was also observed when sintered at 1360 °C. It was considered that charge compensation by doping Sb₂O₃ as well as anomalous grain growth by sintering leads to resistivity reduction from insulating to semiconducting transition.     

Dielectric and impedance properties of Ba2Sr3DyTi3V7O30 ceramics

A new member of tungsten bronze family, Ba₂Sr₃DyTi₃V₇O₃₀, was synthesized by a high-temperature solid-state reaction method. Studies of structural by X ray diffraction technique and micro-structural by scanning electron microscope brings out orthorhombic crystal structure and densely packed nonuniform grains for the above ceramic system. Detailed dielectric studies as a function of temperature (30–500?°C) at different frequencies (1–1,000?kHz) reveals diffuse-phase-transition and loss anomaly at 81?°C. Detailed studies of impedance parameters provide a better understanding of the electrical properties and type of relaxation processes in the material. Temperature variation of dc and ac conductivity shows that this compound exhibits negative temperature coefficient of resistance. The frequency variation of ac conductivity shows that the compound obeys Jonscher’s universal power law.     

复合添加La2O3/MgO对(Zr0.8 Sn0.2)TiO4陶瓷性能的影响

讨论了复合添加La2O3/MgO对(Zr0.8Sn0.2)TiO4介质陶瓷烧结机制和微波介电性能的影响。结果表明,La2O3/MgO对(Zr0.8Sn0.2)TiO4的烧结有一定的促进作用,但La2O3/MgO添加量的增大会造成晶格缺陷和残留气孔的增多,从而导致材料的密度和Q×f降低。在1320℃保温12h、La2O3/MgO添加量为0.9wt%时,(Zr0.8Sn0.2)TiO4介电性能最好,其εr=37.14,Q×f=36600,τf=7.77×10-6/℃。     

High-entropy(Ca0.2Sr0.2Ba0.2La0.2Pb0.2)TiO3 perovskite ceramics with A-site short-range disorder for thermoelectric applications

Novel high-entropy perovskite-type(Ca0.2Sr0.2Ba0.2La0.2Pb0.2)TiO3(CSBLP)ceramics with cubic structure of Pm-3m space group were successful prepared by solid-sta...     

Dielectric properties of (Ba,Sr)O-(Sm,La)2O3-TiO2 ceramics at microwave frequencies

The dielectric properties of (Ba, Sr)O-(Sm, La)₂O₃-TiO₂ material at microwave frequencies were investigated. By varying the amount of strontium from 0–25 mol% in the 0.15(Ba_1–x Sr _x )O-0.15Sm₂O₃-0.7TiO₂ composition, it was possible to adjust the frequency temperature coefficient, _f, from –13 p.p.m. °C^–1 to + 30 p.p.m. °C^–1. When 7 mol% Sr was substituted for barium, _f=0 p.p.m. °C^–1 was obtained. TiO₂ with rutile phase (_f400 p.p.m. °C^–1) acted as a dominant element in _f variation of the 0.15(Ba_1–x Sr _x )O-0.15(Sm_1–y La _y )₂O₃-0.7TiO₂ (0x0.25, 0y0.6) system. Additionally, increasing the quantity of lanthanum substitution for samarium had a greater positive effect on _f than strontium substitution for barium. When 60 mol% La was substituted for samarium with 7mol% Sr substitution barium, _f of the system reached 95 p.p.m. °C^–1. The effect on microwave dielectric characteristics of the 0.15(Ba_0.93Sr_0.07)O-0.15Sm₂O₃-0.7TiO₂ (BSST) ceramics by varying the calcination and/or sintering conditions or doping additives, were studied. The added SnO₂ acted as a firing agent to lower the sintering temperature, and the dielectricQ(Q _d) value was improved by properly adding CdO. With 1 wt% CdO addition, the highestQ _d value of the BSST resonator, after calcination at 1100 °C/2 h and sintering at 1370 °C/4 h, reached 4180 at 4 GHz with a small _f of –4 p.p.m. °C^–1 and an _r of 80.7 was obtained.     

Tuning the microwave dielectric properties of La(Mg0.4Sr0.1Sn0.5)O3 by introducing Ca0.8Sr0.2TiO3

The influence of sintering temperature on the microwave dielectric properties and microstructure of the (1 ? y)La(Mg_0.4Sr_0.1Sn_0.5)O₃–yCa_0.8Sr_0.2TiO₃ ceramic system were investigated with a view to their application in microwave devices. The (1 ? y)La(Mg_0.4Sr_0.1Sn_0.5)O₃–yCa_0.8Sr_0.2TiO₃ ceramic systems were prepared using the conventional solid-state method. The X-ray diffraction patterns of the (1 ? y)La(Mg_0.4Sr_0.1Sn_0.5)O₃–yCa_0.8Sr_0.2TiO₃ ceramic system shifted to higher angle as y increased. A dielectric constant of 41.2, a quality factor (Q × f) of 56,900 GHz, and a temperature coefficient of resonant frequency of ?6 ppm/ °C were obtained when the 0.4La(Mg_0.4Sr_0.1Sn_0.5)O₃–0.6Ca_0.8Sr_0.2TiO₃ ceramic system was sintered at 1,550 °C for 4 h.     

Dielectric properties of Sr3CuNb2O9 perovskite ceramics

The dielectric constant ? and loss tangent tanδ of Sr₃CuNb₂O₉ perovskite ceramics prepared by solid-state reactions have been measured at temperatures from 300 to 900 K and frequencies from 25 to 1 × 10⁶ Hz. The results demonstrate that the samples slowly cooled from the temperature of the final, high-temperature firing (1200°C) have relatively low permittivity (? ? 10) and dielectric losses (tanδ ? 0.005 at 1 kHz) at room temperature, with no strong dielectric dispersion and no prominent maxima in the temperature dependences of their permittivity and dielectric loss. The ceramics quenched from 1300°C exhibit a pronounced Debye-type low-frequency relaxation and strong dielectric dispersion in conjunction with high permittivity ? ? 2000 at low frequencies and/or high temperatures. The observed dielectric anomalies in the Sr₃CuNb₂O₉ ceramics can be understood in terms of Maxwell-Wagner relaxation at dielectric inhomogeneities associated with the quenching-induced difference in oxygen-vacancy concentration between the grain bulk and surface layer.     

Studies on semiconductive (Ba0.8Sr0.2) (Ti0.9Zr0.1)O3 ceramics

In order to produce semiconductive (Ba_0.8Sr_0.2) (Ti_0.9Zr0.1)O₃ ceramics (BSZT), providing low resistivity for boundary-layer capacitor applications, a controlled valency method and a controlled-atmosphere method were applied and studied. In the controlled-valency method, trivalent ions (La³⁺ Sb³⁺) and pentavalent ions (Nb⁵⁺, Sb⁵⁺, Ta⁵⁺) were doped into BSZT ceramics, while in the controlled-atmosphere method, samples were sintered in air and a reducing atmosphere. The doped BSZT ceramics sintered in the reducing atmosphere showed much lower resistivities and smaller temperature coefficient of resistivity (TCR) than those sintered in air, indicating that low partial pressure of oxygen will increase the solubility of the donor dopant and enhance the grain growth. In addition, a small negative TCR at low temperature, as well as a small positive TCR at higher temperature, are also observed for specimens fired in a reducing atmosphere. The former is attributed to the semiconductive grain and the latter to the small barrier layer formed at the grain boundary.     

Enhanced large field-induced strain and energy storage properties of Sr0.6La0.2Ba0.1TiO3-modified Bi0.5Na0.5TiO3 relaxor ceramics

Dielectric materials especially relaxor ferroelectrics with giant strain and super-high energy density have received substantial attentions. Bi_0.5Na_0.5TiO₃ (BNT)-based ceramics as one of the typical relaxor ferroelectric materials have been extensively explored for their distinctive performance. Here, lead-free (1?x)Na_0.5Bi_0.5TiO₃–xSr_0.6La_0.2Ba_0.1TiO₃ (BNT–SLBT) ceramics were designed and prepared by the solid-state reaction method. A large strain response of 0.470% and huge piezoelectric strain coefficient of 600 pm/V were achieved in BNT–0.15SLBT relaxor, which were attributed to the relaxor-ferroelectric phase transition under stimulated electric field. The ε_r–T curve shows that with the increase of x content, the phase transition temperature moves to room temperature, which improves the energy storage performance. A super-high recoverable energy density W_rec of 3.18 J/cm³ and η of 82.8% under 250 kV/cm can be achieved in BNT–0.25SLBT ergodic relaxor. Moreover, the charge–discharge properties characterized by a high pulse discharge energy density (0.816 J/cm³), a rapid discharge duration (3 μs) and a power density (2.86 MW/cm³) are also observed in BNT–0.25SLBT ceramic. We provide a method for enhanced BNT-based ceramics with strain and energy storage in drive device or capacitor, facilitating the exploration of ceramic in the future.

     

Influence of synthesis methods on the dielectric properties of (Ba0.2Pb0.8)TiO3 ceramics

The dielectric properties of (Ba_0.2Pb_0.8)TiO₃ prepared by several methods related to dispersion have been studied. The sol-gel derived specimens without dispersion have lower density, and lower dielectric constant at the Curie temperature. The sol-gel specimens derived from a well-dispersed suspension with pH 11 and 13, and 2% PMMA show higher dielectric constant at the Curie temperature, and higher density, because the grains grow homogeneously in the well-dispersed system. The sol-gel derived specimens have a higher Curie temperature than that of calcined mixed oxides and molten salt synthesis derived specimens.     

La0.8Sr0.2Co0.8Mn0.2O3/SUS430合金连接体制备及微观应变分析

本工作采用溶胶-凝胶提拉法制备了SUS430合金连接体LSCM涂层,探索了涂层的制备工艺,并采用X-ray衍射对涂层进行了分析.通过对涂层X-ray衍射谱的Rietveld拟合,确定了LSCM涂层的精细晶体结构;基于Rietveld拟合得到的洛伦兹峰形展宽参数,计算得到涂层的平均晶粒尺寸;以合金基体相峰形展宽为参照,基于Rietveld拟合和微观应变峰形展宽理论计算得到涂层晶粒内部最大微观应变的方向和大小,分析了涂层中微观应力存在的可能原因.     

钙钛矿型(La0.2Li0.2Ba0.2Sr0.2Ca0.2)TiO3高熵氧化物陶瓷的制备及性能研究

高熵陶瓷是近年来在高熵合金基础上逐渐发展起来的一种新的陶瓷材料体系,它的出现为开发具有优异性能的非金属材料提供了新的理念和路线.本研究采用固相烧结法制备A位等摩尔比的钙钛矿型高熵氧化物陶瓷(La0.2Li0.2Ba0.2Sr0.2Ca0.2)TiO3,并探索了烧结温度对高熵陶瓷的物相结构及电学性能的影响.结果表明,陶瓷...     

溶胶-凝胶法合成La0.9Sr0.1Ga0.8-xAlxMg0.2O3及其性质研究

利用溶胶-凝胶法首次合成了La0.9Sr0.1Ga0.8-xAlxMg0.2O3 (x=0～0.4)系列固体电解质,系统地研究了其晶体结构随Al含量的变化关系.XRD表明1000℃时可形成立方钙钛矿结构,此合成温度明显低于传统固相法所需合成温度(1300～1400℃),且当掺杂量x＞0.1时,即可分辨出杂相.电导率测试表明该体系的电导率与温度的关系是分区间符合Arrhenius定律的,且Al对LSGM中Ga的适量掺杂能有效地促进该体系的离子电导率.     

La0.8Pb0.2Fe0.8Ni0.2O3纳米粉体的制备及其CO气敏性能研究

采用柠檬酸法制备了多晶La0.8Pb0.2Fe0.8Ni0.2O3,并对其结构、电导特性和CO气敏特性进行了研究.结果表明,该材料属正交晶系钙钛矿结构,显示了p型半导体导电特性,并且在工作温度120～340℃范围内对CO气体均具有较高灵敏度,显示出对CO气体的良好气敏性能.