Pb(Zn1/3Nb2/3)O3基复相陶瓷的室温介电老化行为

研究了Ｐｂ（Ｚｎ１／３Ｎｂ２／３）Ｏ３基复相陶瓷的室温介电老化行为与材料烧成制度的关系,性机和介电常数与老化时间的对数值成线性关系,随烧成温度提高和保温时间延长,老化速率增大,老化速率对频率的依存性增加。低温短时间烧结的复相陶瓷的介电老化行为类似于正常铁电体,其老化起因于畴壁运动;而高温长时间烧结的复相陶瓷表现为典型弛豫电体的老化行为,起因于缺陷偶极子与极性微区的相互作用。     

钙铜钛氧高介陶瓷的B位锌掺杂与性能

采用固相反应法制备出B位Zn2+掺杂的CaCu3Ti4O12陶瓷,探讨了其相结构、显微组织和电学性能。Zn2+掺杂后CaCu3Ti4O12陶瓷的介电常数为6 564,10kHz~1MHz频率稳定性好,介电损耗值小于0.4,电学性能的改善与Zn2+掺杂后导致晶粒尺寸增大和晶粒电阻减小有关。通过对CaCu3Ti4-xZnxO12-δ(x=0.03)陶瓷的变温介电频谱分析,得到其介电弛豫晶界热激活能为0.529eV。     

铌鲜酸铅弛豫型铁电陶瓷的介电老化行为研究

通过典型弛豫型铁电陶瓷铌镁酸铅介电老化行为的研究,发现高温区的Ｄｅｂｙｅ型弛豫过程与介电过程电老现象存在有机联系,指出复合钙钛矿弛豫型电体的结构缺陷特征对其介电老化起着重要作用,介电极化行为与老化行为对比分析和恒温经时老化研究表明,外的局域化电子和空穴对铁电微畴畴壁“钉扎”效应产生失电体介电化行为的快过程。     

铌镁酸铅弛豫型铁电陶瓷的介电老化行为研究

通过典型弛豫型铁电陶瓷铌镁酸铅介电老化行为的研究,发现高温区的Debye型弛豫过程与介电老化现象存在有机联系,指出复合钙钛矿弛豫型铁电体的结构缺陷特征对其介电老化起着重要作用.介电极化行为与老化行为对比分析和恒温经时老化研究表明,结构缺陷上的局域化电子和空穴对铁电微畴畴壁"钉扎"效应产生弛豫型铁电体介电老化行为的快过程.     

PMZNT驰豫铁电陶瓷在不同外电场下的介电特性

对PMN－PZN－PT弛豫铁电陶瓷在不同外电场下的介电特性进行了研究。结果表明：直流偏压场与交流测试场对弛豫铁电体的作用相反,增大偏压场导致介电常数的降低,而增大测试场则使介电常数升高。同时频率色散度也呈现了不同的变化趋势。利用超顺电理论及多畴态模型对上述结果进行了定性分析。     

钛酸铋钠系陶瓷固溶改性及介电弛豫性能EI北大核心CSCD

采用电子陶瓷合成工艺制备了致密的钛酸铋钠基固溶陶瓷(1–x)(Na_(0.5)Bi_(0.5))TiO_3–xLa(Zn_(0.5)Ti_(0.5))O_3,研究了该系陶瓷的相组成、微观形貌及介电性能。结果表明:在(Na_(0.5)Bi_(0.5))TiO_3中引入La(Zn_(0.5)Ti_(0.5))O_3后形成了单相钙钛矿固溶体;随着La(Zn_(0.5)Ti_(0.5))O_3引入量的增加,晶粒形貌由球状向立方体状转变,晶棱显著锐化,晶粒细化,尺寸更加均匀;La(Zn_(0.5)Ti_(0.5))O_3的引入使得(Na_(0.5)Bi_(0.5))TiO_3晶体中氧空位增多以及A、B位离子种类增多,晶体结构中离子分布无序化程度加剧,致使该系陶瓷的介电频率色散显著,介电弛豫激活能降低(从1.7 e V降低至1.32 e V),弛豫性增强。     

晶粒尺寸对Ba0.80Sr0.20TiO3陶瓷介电铁电特性的影响

利用微波烧结技术和传统烧结技术制备了晶粒尺寸在0.8～15μm的Ba0.80Sr0.20TiO3陶瓷，并对样品的介电特性和铁电特性进行了测试，分析了晶粒尺寸对材料介电和铁电性能的影响，实验结果表明，微波烧结技术可以有效地控制Ba0.80Sr0.20TiO3陶瓷的晶粒尺寸，晶粒尺寸降低，材料的介电常数大幅度提高，弥散指数降低，在外电场作用下，材料介电常数呈现明显的非线性效应，晶粒尺寸的大小对非线性效应产生影响，随晶粒尺寸的降低，材料的矫顽电压，剩余极化和自发极化都有所提高。     

晶粒状态对LiTaO3电畴结构的影响

通过TEM技术研究了Al2O3/LiTaO3陶瓷复合材料中LiTaO3颗粒内的电畴结构,并将LiTaO3单晶、LiTaO3作为基体和LiTaO3作为第二相时其晶粒内的电畴结构进行比较。观察表明:纯LiTaO3陶瓷内的电畴结构基本上为曲流状180°电畴,也有非常少量的非180°电畴;15ALT陶瓷复合材料可看出LiTaO3晶粒内非180°电畴明显增多,且板条状与尖劈状两种状态都存在,但其中曲流状180°电畴明显可见;30ALT陶瓷复合材料中,只有少量的曲流状180°电畴,其中非180°电畴是这几个组分中数量最多、分布最密集的。LiTaO3晶粒内部电畴的形成与周围颗粒对其约束产生的应力有关。     

Na-Zr替代对Bi_2(Zn_(1/3)Nb_(2/3))_2O_7陶瓷性能的影响

研究Na+替代Bi3+、Zr4+替代Nb5+对铋锌铌基陶瓷烧结特性、显微结构和介电性能的影响。结果表明:替代后样品的烧结温度从1000℃降低到880℃;在-30～+130℃,样品温谱出现明显的介电弛豫现象;弛豫峰值温度随Zr4+替代量增加向高温方向移动,弛豫过程的激活能在0.3eV左右。用缺陷偶极子和晶格畸变对Na-Zr掺杂Bi2(Zn1/3Nb2/3)2O7的介电弛豫现象作出解释。     

(Bi_(0.5)Na_(0.5))TiO_3-BaTiO_3系陶瓷的介电弛豫性能

采用传统压电陶瓷固相合成法制得了纯钙钛矿相的( 1 -x) (Bi0 5Na0 5 )TiO3 -xBaTiO3 (x=0 02, 0 04,0 06, 0 08, 0 10) (简写作BNBT)系无铅压电陶瓷。研究了1kHz条件下室温到400℃的温度范围内BNBT试样的介电温谱以及3种不同频率下(1、10、100kHz)BNBT-6试样的介电温谱,发现材料在研究组成范围内均为弛豫型铁电体。采用HRTEM研究了该系统的畴结构,表明BNBT钙钛矿结构铁电体的介电性能与复合离子的有序无序排列密切相关,纳米尺度有序微畴对介电弛豫起着重要作用。     

Polar nano-clusters in nominally paraelectric ceramics demonstrating high microwave tunability for wireless communication

Dielectric materials, with high tunability at microwave frequencies, are key components in the design of microwave communication systems. Dense Ba_0.6Sr_0.4TiO₃ (BST) ceramics, with different grain sizes, were prepared in order to optimise the dielectric tunability via polar nano cluster effects. Dielectric permittivity and loss measurements were performed at both high and low frequencies and were supported by results from X-ray powder diffraction, scanning and transmission electron microscopies, Raman spectroscopy and piezoresponse force microscopy. The concentration of polar nano clusters, whose sizes are found to be in the range 20–50 nm, and the dielectric tunability increase with increasing grain size. A novel method for measurement of the microwave tunability in bulk dielectrics is presented. The highest tunability of 32 % is achieved in ceramics with an average grain size of 10 μm. The tunability of BST ceramics with applied DC field is demonstrated in a prototype small resonant antenna.     

Frequency-dependent Qf value of low-loss Ba2Ti9O20 ceramics at microwave frequencies

The microwave dielectric properties of low-loss Ba₂Ti₉O₂₀ ceramics were evaluated by the resonant cavity method, and the frequency dependence of Qf value was investigated. TE₀₁₁ resonant mode was used for measurement, and the measurement frequency was changed by adjusting the sample size. The measurement frequency could also be tuned over a wide range by using higher-order TE_0np modes for a sample with a fixed size. The measured Qf value of Ba₂Ti₉O₂₀ ceramics increased significantly with increasing the frequency from 4.55 to 10.74 GHz. The result conflicted with the common recognition that the Qf value of microwave dielectric ceramics was a frequency-independent constant at microwave frequencies. The frequency dependence of Qf value was attributed to the extrinsic dielectric loss, which originated from extrinsic factors such as grain boundary, oxygen vacancy and pore.     

通信用片式介质陶瓷双工器的设计与制作

介绍了通信用介质陶瓷双工器的设计方法和制作过程。该双工器是由接收滤波器和发射滤波器组成的。每种滤波器是由一块高介电常数、高Q值和接近零温度系数的介质陶瓷块制成的。这个陶瓷块上包含两个四分之一波长同轴谐振腔、输入及输出电极和耦合装置,并且输入及输出电极在陶瓷块的同一侧面上,因此滤波器具有体积小巧,结构稳定和安装方便的特点。采用介电常数为90的陶瓷材料制作了中心频率分别为903MHz和927MHz的接收和发射滤波器,经网络分析仪测试,各项技术指标满足设计要求。     

Impedance spectroscopy studies on samarium and sodium substituted strontium bismuth titanate (SBTi)

Sr_1-x Sm_xNa_xBi₄Ti₄O₁₅ lead-free piezoelectric ceramics are prepared by solid-state sintering method using high energy Ball- Mill and ground for 10 h. The single phase of the compound is confirmed by X-ray Diffraction and highest intensity peak (1 1 0) is observed at 30°. Diffraction peaks shifted towards higher angles with an increasing concentration of Sm³⁺ and Na¹⁺ of SBT. Grains orientation and grain size are analyzed by Scanning Electron Microscope. Temperature and frequency dependent AC conductivity studies are carried out using impedance spectroscopy in the temperature range of 30 °C–650 °C using Wayn-Kerr LCR meter. At lower frequencies, conductivity is independent of frequency. The variation of Z″ with frequency shows peaks shifting towards higher frequencies with an increase of temperature. The resistance of grains (R_g), grain boundaries (R_gb) are calculated and it is found that grain resistance is greater than grain boundary resistance (R_g > R_gb). Relaxation times of grain and grain boundaries are calculated.     

CaCu3-xMnxTi4O12陶瓷的介电性能研究

本文利用固态反应法制备了CaCu3-xMnxTi4O12(x=0,0.2,0.4,0.6,0.8,1.0)陶瓷,并分析探讨了MnO添加量对其介电性能的影响。研究结果表明,MnO的添加有助于CaCu3Ti4O12相生成,且在高MnO添加的情况下所得陶瓷晶粒尺寸较小。MnO的添加对CaCu3Ti4O12的介电性能有非常不好的影响,少量的添加就会导致其介电常数由10000多降至只有数百。在1000Hz前MnO的添加会使陶瓷的介电损耗大幅上升,这表明MnO添加有降低电阻的效果。     

Grain size effect on electrical and reliability characteristics of modified fine-grained BaTiO3 ceramics for MLCCs

Fine-grained BaTiO₃-based ceramics of different grain sizes (118–462 nm) with core–shell structures were prepared by a chemical coating method, having good dielectric properties and gentle temperature stability. The grain size effect on the dielectric properties and insulation resistivity of modified fine-grained BaTiO₃ ceramics under high temperatures and electric fields were investigated. The DC bias shows a strong effect on the dielectric properties with decreasing grain size. In the finest ceramics, the absolute value of the capacitance stability factor was the smallest, indicating that the modified-BaTiO₃ ceramic capacitor with smaller grains had higher reliability under the DC bias voltage. The highly accelerated lifetime test results showed that with decreasing the grain size, samples exhibited higher insulation resistance under elevated temperatures and high voltages. Impedance analysis proved that the finer-grained ceramic with core–shell structure had higher activation energy for both grain and grain boundary, whereas the proportion of ionic conductivity was lower.     

Effect of the ac Field Level on the Aging of the Dielectric Response in Polycrystalline BaTiO3

BaTiO₃ ceramics with grain sizes from 0.6 to 60 μm and relative densities of 89% to 92% were prepared by hot forging and conventional sintering from very pure-oxalate-derived powder. The aging of both the dielectric constant and the dielectric loss was examined at weak and strong fields with respect to grain size and frequency. It was concluded that the main aging mechanism is the aging of hysteretic domain wall motion for coarse-grained ceramics. At grain size of less than 1 μm, the lack of frequency and E _AC dependence, along with a lower aging rate, suggests that domain motions or hysteretic domain wall motions are restricted in finegrained ceramic BaTiO₃ and contribute little to the aging.     

Colossal dielectric permittivity and relevant mechanism of Bi2/3Cu3Ti4O12 ceramics

Bi_2/3Cu₃Ti₄O₁₂ (BCTO) ceramics with pure perovskite phase were successfully prepared by traditional solid-state reaction technique. Uniformly distributed and dense grains with the grain size of 2–3 μm were observed by SEM. A giant low-frequency dielectric permittivity of ~3.3×10⁵ was obtained. The analysis of complex impedance revealed that Bi_2/3Cu₃Ti₄O₁₂ ceramics are electrically heterogeneous. There are three kinds of dielectric response detected in Bi_2/3Cu₃Ti₄O₁₂ ceramics, which existed in the low-frequency range, middle-frequency range, and high-frequency range, respectively. Through the study of dielectric spectrum at different temperatures, the relatively low activation energy of 0.30 eV for middle-frequency dielectric response was calculated, which suggested that this Middle-frequency dielectric response can be ascribed to grain boundaries response. In view of the analysis of dielectric spectrum at low temperatures, the activation energy of 0.07 eV for high frequency dielectric response was found. This value illustrated that dielectric response at high frequencies was associated with grains polarization effect. The comparison of dielectric spectra of Bi_2/3Cu₃Ti₄O₁₂ ceramics with different types of electrodes revealed that giant low-frequency dielectric constant was attributed to the electrode polarization effect.     

Aging of the Weak-Field Dielectric Response in Fine- and Coarse-Grain Ceramic BaTiO3

BaTiO₃ ceramics with grain sizes of 0.6 to 6 mm and relative densities of 89% to 92% were prepared by hot forging and conventional sintering from high-purity oxalate-derived powder. The aging of both the dielectric constant and the dielectric loss was examined with respect to grain size, temperature, and frequency. It is suggested that the main aging mechanism in coarse-grained BaTiO₃ is the aging of hysteretic domain wall motion. The dielectric aging is a thermally activated process and shows two aging rates when observed at a temperature of 8°C for coarse-grained ceramics.     

Preparation, Characterization, and Properties of Dy-Doped Small-Grained BaTiO3 Ceramics

The effects of Dy doping and sintering parameters on the properties of BaTiO₃ ceramics were studied. The average grain size decreases with increasing Dy content and is controlled at ∼1.5 μ m by 0.8 at.% Dy. The Curie temperature change, associated with ≤1.2 at.% Dy, is <3°C. The dielectric constant is ∼2600 for specimens doped with 0.8 at.% Dy, calcined at 1200°C, and sintered at 1450°C. The dielectric constant variation with ambient temperature is much less than that of conventional BaTiO₃ ceramics. Lattice constant c decreases with increasing Dy concentration whereas a increases slightly. The effects of grain size on dielectric constant, lattice parameters, and linear thermal expansion coefficient are more pronounced than the chemical effects of Dy doping in the ferroelectric state, whereas in the paraelectric state, these characteristics are almost independent of grain size as well as Dy concentration. The decrease in the frequency of occurrence of 90° twins with decreasing grain size implies that internal stress, which develops when BaTiO₃ ceramics are cooled below T_c , strongly influences the effects of grain size.