Investigation of Semiconducting Barium Titanate Ceramics by Oxygen Coulometry

Donor-doped BaTiO₃ ceramics (0–0.6 mol% Nb) were investigated during the sintering process at an oxygen partial pressure of 2.4 Pa and at a maximum temperature of 1430C. The occurring oxygen exchange with the ambient atmosphere was monitored quantitatively by oxygen coulometry. The coincidence between the grain growth behavior and the occurrence of distinct oxygen release peaks during the anomalous grain growth reveals that significant amounts of the donor are incorporated and charge-compensated by electrons only under the conditions of the anomalous grain growth. Quantitative analysis of the coulometric data shows that at a doping level of 0.2 mol% nearly all donors are charge-compensated by electrons. With increasing Nb concentration also Ti vacancies gradually begin to serve for compensation. At 0.5 mol% Nb their influence reaches 70 % of the electronic compensation.     

改性对钛酸钡陶瓷介电常数的影响

钛酸钡(BaTiO3)陶瓷以其优异的铁电、压电、绝缘性能广泛应用于体积小、容量大的电子器件材料领域,为解决钛酸钡(BaTiO3)陶瓷在一定的工作温度区间介电常数呈现不稳定变化问题,对其进行改性,着重研究稀土掺杂改性对BaTiO3陶瓷介电性能的影响,并对目前存在的问题提出了解决的方法。     

混料次序对钛酸钡介电性能的影响

通过改变混料的次序以及采用沉降、水煮损耗、温度特性、电导率和化学分析等测试手段,研究了制备钛酸钡的球磨工艺中混料次序对钛酸钡粉体均匀性及钛酸钡介电性能的影响。研究结果表明:采用不同的混料次序制得的钛酸钡性能差别较大,先钡后钛的方式较优,能减少球磨引起的团聚,极大地改善了固相合成BaTiO3粉体均匀性,提高了钛酸钡的介电性能。     

微波烧结高介电常数钛酸钡复合材料的研究

分别采用微波烧结和传统烧结的方法对钛酸钡复合材料进行烧结。从微观结构、烧结后样品的收缩率、样品的电容以及介质损耗因数等几个方面进行了比较分析。结果表明：微波烧结比传统烧结得到的样品具有更致密、更均匀的微观结构。微波烧结对样品线性收缩率终值影响不大,但会增强烧结密度,使开始收缩温度降低20～25℃,得到的样品具有更小的介质损耗。     

Electrical Properties of Bismuth Titanate Based Ceramics with Secondary Phases

Bi₄Ti₃O₁₂ (BIT) based ceramics were prepared by hydroxide coprecipitation method and subsequent treatment at 650C for 1 h. Calcined BIT was doped with different amounts of WO₃ by surface doping using W(C₂H₅O)₆. The amount of dopant modified the sintering behaviour of BIT-based ceramics through a liquid-phase assisted sintering mechanism in the case of low dopant concentration and Zenner effect when high concentration of dopant was used. Consequently, the microstructure and the electrical properties were strongly dependent on the dopant concentration. Doped BIT-based ceramics showed a microstructure composed of very small platelet-like grains and the electrical conductivity was markedly decreased. The high electrical resistivity makes possible the polarization of doped ceramics and relatively good piezoelectric parameters were measured.     

锡钛酸钡薄膜材料的研究现状

铁电薄膜是一类重要的功能材料,其中锡钛酸钡（BTS）薄膜由于具有较优异的介电性能而成为研究热点。本文综述了锡钛酸钡薄膜材料的制备方法和介电性能的研究现状,提出了研究中需要解决的问题。     

Effect of Zr/Ti Ratio on Microstructure and Electrical Properties of Lead Zirconate Titanate Thin Films Derived by Pulsed Laser Deposition

PZT films were fabricated using various targets of Pb(Zr_xTi_{1 – x})O₃ with Zr/Ti ratios of 70/30, 58/42, 52/48, 45/55 and 30/70, and with excess PbO of 20 wt% on Pt/Ti/SiO₂/Si(100) substrates. The rosette structure was observed in the films derived from the target with a Zr/Ti ratio of 70/30 and disappeared with increasing titanium composition. The observations on surface and cross-sectional microstructure were consistent with a higher perovskite nucleation for the higher Ti content films. The PZT films derived from the target with a Zr/Ti ratio of 45/55 had a polycrystalline columnar microstructure extending throughout the thickness of the film and no pyrochlore phase on the surface was observed. The PZT films derived from the target with a Zr/Ti ratio of 45/55 exhibited better electric properties than those derived from the target with a Zr/Ti ratio of 52/48.     

Chemical Variations in Barium Titanate Powders and Dispersants

Commercial raw materials for multilayer ceramic capacitors—barium titanate (BT) and ammonium polyacrylate (APA) dispersant—were examined for lot-to-lot variations which cause poor reproducibility in BT slips and in capacitor chips. Two lots of BT supplied by a commercial source were different with respect to surface species examined by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, electrokinetic sonic amplitude and total carbon analysis. It was found that there was more APA dispersant chemisorption on BT when the BT surface was more hydroxylated and less carbonated. For the dispersant, the two lots differed in pH and ammonium ion content. The amount of APA dispersant adsorbed on BT depended more on the ceramic powder surface species than on the chemical differences in APA lots.The electrokinetic sonic amplitude (ESA) and zeta potentials of the two lots of as-received BT were small but positive. The BT lot with more surface hydroxyls exhibited slightly higher zeta potential values. The BT with more carbonate was more stable in terms of aging rate in water. Aging in water increased the positive zeta potential by increasing Ba²⁺ dissolution and adsorption. With the APA dispersant, the BT surface became less positive, but more stable and exhibited an isoelectric point of10.6. It can be concluded that the dispersion of BT in the as-dispersed pH range is mainly by steric stabilization with little contribution from electrostatic charges.     

Dielectric Properties of Niobium and Lanthanum Doped Lead Barium Zirconate Titanate Relaxor Ferroelectrics

The lead barium zirconate titanate (PBZT) relaxor ferroelectrics are ideal for high voltage capacitor applications due to their high dielectric constant, stability under DC bias, and temperature stability. In this study the composition (Pb_0.65Ba_0.35)(Zr_0.70Ti_0.30)O₃ was selected as the base composition. It exhibited typical relaxor characteristics such as frequency dispersion and diffuse phase transition. The dielectric constant is 6000 at room temperature and remains almost constant under electric field as high as 20 kV/cm. To further enhance the dielectric properties, various amounts of niobium oxide and lanthanum oxide dopants were added to the base PBZT to alter the defect structure and hence the dielectric properties. It was found that the dielectric constant of 1% Nb-doped samples was increased by 20–25% while maintaining similar voltage stability. This increase was attributed to the abnormal grain growth in the Nb-doped sample, and the correlation between microstructure and dielectric constant was drawn through a grain size study. The La addition only caused a monotonic decrease of dielectric constant and slightly improved voltage stability.     

Copper Compatible Barium Titanate Thin Films for Embedded Passives

Barium titanate thin films have been prepared by chemical solution deposition on 18 m thick, industry standard copper foils in the absence of chemical barrier layers. The final embodiment exhibits randomly oriented BaTiO₃ grains with diameters between 0.1 and 0.3 m, and an equiaxed morphology. The average film thickness is 0.6 m and the microstructure is free from secondary or interfacial phases. The BaTiO₃ films are sintered in a high temperature reductive atmosphere such that copper oxidation is avoided. Subsequent lower-temperature, higher oxygen pressure anneals are used to minimize oxygen point defects. Permittivities of 2500 are observed at zero bias and room temperature, with permittivities greater than 3000 at the coercive field. Loss tangents under 1.5% are demonstrated at high fields. The BaTiO₃ phase exhibits pronounced ferroelectric switching and coercive field values near 10 kV/cm. Temperature dependent measurements indicate a ferroelectric transition near 100C with very diffuse character. Combining the approaches of the multilayer capacitor industry with traditional solution processed thin films has allowed pure barium titanate to be integrated with copper. The high sintering temperature—as compared to typical film processing—provides for large grained films and properties consistent with well-prepared ceramics. Integrating BaTiO₃ films on copper foil represents an important step towards high capacitance density embedded passive components and elimination of economic constraints imparted by traditional noble metallization.     

成型压力对钛酸锶陶瓷电容器介电性能的影响

研究了不同的成型压力对钛酸锶陶瓷电容器介电性能的影响。借助扫描电镜和宽频介电测试仪研究陶瓷的微观结构及其介电性能。实验结果表明,当成型压力从5 MPa增加到6 MPa时,坯体的密度突然增大,6 MPa以后密度增加缓慢;1380℃烧结后,成型压力为6 MPa时试样的介电性能最佳。     

Characterization of Barium Titanate: BaTiO<Subscript>3</Subscript> (BT) Ceramics Prepared from Sol-Gel Derived BT Powders

Sol-gel synthesis was attempted at room temperature by adding drop wise a clear solution (made by reacting BaCO₃ with glacial acetic acid) to an equi-molar solution of titanium tetrabutoxide in isopropanol (IPA) and acetic acid. The gelation occurred within 30 minutes. The as-dried gel was calcined at 750^∘C/6 h in air to obtain carbon free BaTiO₃ powders. The resulting BT powders were further pressed into pellets and sintered at 1280^∘C/4 h in air to get dense ceramics (density ∼ 94%). XRD and SEM techniques were used for phase and microstructure analysis respectively. The room temperature relative permittivity (ε) of 1280 increased to 7200 (at Curie temperature of 127^∘C) at 1 kHz frequency. The dissipation factor (tanδ) ∼1.6% was observed in these samples. Also, the ferroelectric properties such as spontaneous polarization (Ps ∼ 13 μC/cm²), coercive field (E_c∼4.0 kV/cm) and dielectric strength (∼34 kV/cm) are estimated for these samples. These performance parameters are compared with the available standard data from the literature.     

Ferroelectric and dielectric properties of sol-gel and excimer-laser-deposited lead zirconate titanate and barium titanate films

Abstract

Switched remanent polarization was measured as a function of accumulated switching cycles for a variety of ferroelectric films using sinusoidally driven hysteresis loops. Switched remanent polarization and dielectric constant and loss were also obtained as a function of the cycling frequency. PZT films with niobium additives appeared to lose switched remanent polarization with accumulated cycles at a lesser rate than films without niobium. The switched remanent polarization was found to decrease with increasing frequency, which we attribute to the effect of grain size. Also, a decrease of dielectric constant with increasing frequency and an increase of dielectric constant with increased applied voltage are attributed to the effects of domain wall motion contributions to dielectric constant.     

低温烧结新型钛酸钡陶瓷复合材料的介电性能研究

为降低片式多层陶瓷电容器(MLCC)的成本,研究了适宜低温烧结的陶瓷复合材料配方。向钛酸钡中添加不同的无机填料,对浆料进行球磨,然后将研磨好的浆料进行压片,低温烧结,制备出适宜低温烧结的陶瓷复合材料,并对其形貌、强度、介电性能和工艺进行研究。结果表明:添加水玻璃和无机硅胶能使钛酸钡烧结后形成致密的片材强度大、硬度高、不易碎裂;而添加石墨和蒸馏水则不易形成稳定型片材,强度差;添加水玻璃可以使复合材料的介电常数显著增加,水玻璃的最佳添加量为3%。     

Processing Effects on the Microstructure and Dielectric Properties of Barium Strontium Titanate (BST) Ceramics

Barium Strontium Titanate (BST) ferroelectric thick films have been investigated as potential candidates for use in frequency agile microwave circuit devices. Powder processing techniques such as screen-printing have been used to make BST thick films. However, due to the interactions between the BST and substrates such as alumina, the sintering temperatures for the BST thick films are limited and the resultant films are difficult to achieve full densification. In this paper, the effects of different powder processing conditions (calcination, sintering temperature and time) on the sintering behaviour and dielectric properties of the BST ceramics have been investigated. The dielectric behaviour of the ceramics has been correlated with composition and microstructural features such as chemical homogeneity, grain size and domain wall movements.     

钛酸铋钙和稀土复合掺杂对BaTiO3陶瓷微结构和介电性能的影响

研究了稀土及CaBi4Ti4O15（CBT）的复合掺杂对BaTiO3（BT）陶瓷微结构及介电性能的影响。结果表明：单独添加CBT使晶粒细化,促进了陶瓷的烧结致密化,居里温度随着CBT含量的增加（≤0．5mol％）而逐渐移向高温端;当CBT含量由0．3mol％增加到0．5mol％时,BT陶瓷的电容量变化率逐渐减小;当CBT含量超过0．5mol％时,电容量变化率又增大。在BaTiO,CBT（BT—CBT）基础上单独添加1．0mol％La2O3,四方率减小,居里点移向低温端;保持La2O3掺杂量不变,随着CeO2含量的增加,BT—CBT陶瓷的晶胞体积呈现先减小后增大的变化趋势,四方率保持不变;1．0mol％La2O3和0．01mol％CeO2掺杂BT—CBT（0．5m01％）陶瓷在-55℃和125℃的电容变化率分别为-14．78％和-11．44％。完全符合EIAX7R标准,有望用于X7R型多层陶瓷电容器的制备。     

Dielectric Characteristics and Tunability of Barium Stannate Titanate Ceramics

Ba(Ti_{1 –x} Sn _x )O₃ solid solutions were prepared by a solid state reaction method, and their dielectric and tunable characteristics were investigated together with the microstructures and diffused phase transition behaviors. The dielectric relaxation behaviors were observed and became stronger with increasing x.The obvious field dependence of the present system was observed with high dielectric constant and low loss at relatively lower DC electric field. The excellent tunable dielectric characteristics were achieved for x= 0.15 at room temperature: tunability 56%, tan 0.003 at 10 kHz under 7.6 kV/cm, indicating that it is a promising candidate for electric-field tunable dielectrics working at room temperature.     

Al2O3不同掺杂方式对钛酸钡介电性能的影响

采用固相法制备了掺杂1 mol%Al2O3和1mol%Al2O3-2mol%BaO两组钛酸钡陶瓷样品。结果表明:Al2O3两种掺杂方式对钛酸钡的作用效果存在差异,其中Al2O3-2BaO共掺杂的作用效果较强,这与不同掺杂方式所引起的钛酸钡陶瓷的晶格变化差异有关。两种掺杂方式均使钛酸钡陶瓷的εmax减小,居里温度降低,介质损耗降低,同时伴有介温峰展宽,且由于弥散相变的存在其室温介电常数呈增大之势。     

Dielectric properties of nanocrystalline barium zirconate titanate synthesized by glycine-nitrate autocombustion

Abstract

Dielectric properties of nanocrystalline barium zirconate titanate (Ba(Zr_xTi_1-x)O₃; BZT for x?=?0.1 and 0.3) synthesized by glycine-nitrate autocombustion method were investigated in this study. The phase formation examined by TGA-DTA, XRD, FT-IR and Raman spectroscopy confirmed that high purity single-phase BZT with perovskite structure was obtained by using glycine-to-nitrate molar ratio of 2.2:4 and calcining in air at 1100?°C for 4?h. TEM analysis showed that BZT had agglomerate particles consisted of primary spherical nanocrystals with the size of 8-11?nm. The diffuse phase transition behavior of BZT ceramics increased with increasing Zr concentration and for x?=?0.3, the Curie temperature; T_c, shifted to below room temperature. The BZT ceramics for x?=?0.1 had relatively high dielectric constant (ε), 13007, low T_c, 76?°C and comparable dielectric loss (tan δ) at T_c, 0.012 which caused by the high degree of Zr diffuseness into the perovskite structure. These results suggest that glycine-nitrate autocombustion is the effective method for preparing high quality BZT ceramics.     

碳酸钡特性对高介钛酸钡陶瓷性能的影响

分析了不同产地的碳酸钡原料的物理特性及不同碳酸钡对陶瓷性能的影响。结果表明,杂质含量低、球形颗粒的碳酸钡原料能显著降低陶瓷的水煮损耗,但陶瓷水煮损耗异常和其致密性不存在对应关系。颗粒细小的碳酸钡原料能使介电温谱变得更平缓。