XRD studies on barium titanate (BaTiO3)/polyvinylidene fluoride (PVDF) composites

XRD studies were carried out on barium titanate (BaTiO₃)/polyvinylidene fluoride (PVDF) composites in the ranges 98° to 103° and 10° to 50°. The structures of PVDF/BaTiO₃ composites were affected significantly. In the composites, elimination and suppression of some of the peaks of PVDF and shifting of some of the peaks of BaTiO₃ was observed. The observed changes are attributed to the internal stresses.     

多巴胺改性BaTiO_3对BaTiO_3/PVDF复合材料击穿场强的影响

为了提高BaTiO3/PVDF复合材料的击穿场强。首先,利用多巴胺对BaTiO3进行表面功能化处理,得到多巴胺改性的BaTiO3(Dopa@BaTiO3);然后,将其与聚偏氟乙烯(PVDF)混合,采用液相浇铸法制得Dopa@BaTiO3/PVDF复合材料;最后,测量了不同Dopa@BaTiO3添加量的Dopa@BaTiO3/PVDF复合材料的击穿场强和介电性能。结果表明:与改性前的BaTiO3/PVDF复合材料相比,Dopa@BaTiO3/PVDF复合材料在击穿场强显著提高的同时,介电常数基本保持不变;当Dopa@BaTiO3添加量为3vol%时,击穿场强为210kV/mm,比改性前的复合材料的提高了78%;当Dopa@BaTiO3添加量为10vol%时,击穿场强为180kV/mm,比改性前的合材料的提高了88%。研究解决了BaTiO3/PVDF复合材料击穿场强较低的问题,可为同时提高复合材料的介电常数和击穿场强提供参考。     

Charge-field hysteresis of BaTiO3: PVDF composites

Hysteresis phenomena in BaTiO₃: PVDF composites with different weight fractions of BaTiO₃ and PVDF were studied in the temperature range 20–180°C. A sinusoidal electric field of up to 100 kV ^–1 at 50 Hz was used. The saturation polarization, P _sat, remanant polarization, P _r, and coercive field, E_c, were observed to increase with increasing ceramic content of the composite samples. An increase of polarization with temperature was observed for all composites up to 80°C. This has been explained on the basis of an increase in the conductivity of the PVDF phase.     

Effect of the dispersibility of BaTiO3 nanoparticles in BaTiO3/polyimide composites on the dielectric properties

We have investigated the effect of coupling agents with different organic moiety on the dielectric properties of polyimide/BaTiO₃ (70 nm) composite films. INAAT (isopropyl tris(N-amino-ethyl aminoethyl)titanate, KR 44) and APTS (3-amino-propyl-triethoxysilane) were used as coupling agents, respectively, for homogeneous dispersion of BaTiO₃ particles into a polyimide matrix. The composite films were prepared by pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA)-based polyimide. Enhanced dispersion of BaTiO₃ particles was obtained by the use of INAAT with more organic moiety compared to that afforded by APTS. The polyimide composite with BaTiO₃ particles (BaTiO₃ content at 50 vol.%) treated by INAAT showed an increased dielectric constant of 19.03 while retaining an appropriate dielectric loss of 0.0109, as compared to the dielectric constant (14.64) of polyimide/APTS-treated BaTiO₃ composite. The results of this work demonstrate the potential use of an INAAT coupling agent with more organo functional groups for obtaining enhanced dielectric properties in a polyimide/BaTiO₃ composite for application in an embedded capacitor.     

钛酸钡/环氧介电复合材料制备技术的研究

以环氧树脂作为基体、双氰胺和2-乙基-4-甲基咪唑作为固化剂体系、颗粒尺寸在38.0nm～2.67μm范围的钛酸钡(BaTiO3)作为高介电填充组分,采用溶液共混合旋涂工艺,制备了不同BaTiO3含量的0-3型BaTiO3/环氧复合材料膜,研究分析了环氧树脂固化工艺的确定以及不同BaTiO3含量的复合材料的晶相及显微结构.研究表明,固化剂体系含量占环氧树脂质量分数为6%时,固化温度约120℃(1h);受钛酸钡粒子的影响,复合材料基体相聚合物有序排列的分子结构被破坏,环氧树脂分子链的排列密度降低;BaTiO3质量分数为0.6时,复合材料中陶瓷粉末的分散效果最佳.     

双马来酰亚胺/钛酸钡复合材料介电性能的研究

以双马来酰亚胺（BMI）为树脂基体，压电陶瓷BaTiO，为功能填料，采用浇铸的方法制备了BMI/BaTiO3复合材料。考察了复合材料的介电性能，并用多种混合法则对复合材料的介电常数进行拟合分析。研究结果表明，BaTiO3含量的增加提高了材料的介电常数，同时增加了材料的介电损耗；BMUBaTiO3复合材料的介电性能具有良好的频率稳定性：使用Lichterecker混合规则的拟合结果与实验测试结果具有很好的一致性。     

Effects of particle size of BaTiO3 powder on the dielectric properties of BaTiO3/polyvinylidene fluoride composites

The effects of particle size of fine BaTiO₃powder on dielectric properties of BaTiO₃/polyvinylidene fluoride (PVDF) composites were investigated. When the frequency of the applied field was less than 100 kHz, the dielectric constant and loss for BaTiO₃/PVDF composites decreased with increasing BaTiO₃particle size. When the frequency was greater than 100 kHz, the opposite results were obtained. The resistivity increased with increasing BaTiO₃particle size, whereas the open areas of hysteresis loops decreased gradually. The degree of poling efficiency for BaTiO₃/PVDF composites increased with increasing BaTiO₃particle size. The BaTiO₃particle size dependence of the dielectric properties of BaTiO₃/PVDF composites is explained by space charge effects at the interface between BaTiO₃and PVDF, and domain configurations (single or multi-domain) of the BaTiO₃powders.     

Low-field magnetoresistance in La0.7Sr0.3MnO3/BaTiO3 composites

A manganite composite series of (1 ? x)La_0.7Sr_0.3MnO₃/xBaTiO₃ (x = 0, 0.06, 0.12, and 0.18) has been fabricated by solid-state reaction combined with a high-energy mechanical milling method. Experimental results revealed that the insulator–metal transition temperature was shifted towards lower temperatures, and resistivity increases with increasing BaTiO₃ content in (1 ? x)La_0.7Sr_0.3MnO₃/xBaTiO₃. Meanwhile, the ferromagnetic–paramagnetic transition temperature was almost unchanged. The increase in magnetoresistance was observed in the all composites at whole measurement temperatures under an applied magnetic field of 3 kOe. Here, temperature dependences of magnetoresistance display a Curie–Weiss law-like behavior. The nature of this phenomenon is explained in detail.     

Preparation and properties of polymer matrix piezoelectric composites containing aligned BaTiO3 whiskers

A piezoelectric composite has been prepared with highly aligned BaTiO₃ whiskers as the active phase and polyvinylidene fluoride (PVDF) as the matrix. Its dielectric and electromechanical properties are characterized. It is found that the dielectric constant (), piezoelectric constant (d ₃₃) and remnant polarization (Pr) are considerably higher in the whisker composite than in the corresponding composite containing BaTiO₃ powders as the active phase, while the loss factors follow the opposite trend. For the whisker composite, , d ₃₃ and Pr along the direction of the whisker orientation are much higher than the values normal to the whisker orientation. The reasons for the observed differences are discussed.     

Influence of adsorbed moisture on the properties of cyanate ester/BaTiO3 composites

The effect of moisture adsorbed on BaTiO₃ on the properties of cyanate ester (CE)/BaTiO₃ dielectric composites is examined using undried and dried BaTiO₃ particles. The influence of moisture on the dielectric constant, thermal stability, dynamic mechanical properties, flexural behavior and micro morphology of the composites is investigated. Dielectric constant (ε) and dielectric loss (tan δ) of composites with the dried BaTiO₃ are both higher than composites manufactured with undried filler at the same frequency. The dielectric properties of the dried system are stable over a broader temperature range than the undried composites. Adsorbed moisture causes the initial decomposition temperature and the maximum degradation temperature of the composite to decrease by 27 °C and 15 °C, respectively. By removing the moisture from BaTiO₃, the CE/BaTiO₃ composite exhibits a lower modulus (E′), higher strength, higher flexural elongation and a dramatically increased glass transition temperature (T_g).     

纳米钛酸钡及其复合湿敏材料的IR与XPS谱分析

由纳米钛酸钡与高分子季胺盐型丙烯酸树脂（RMX）构成的复合材料的湿敏性能优于纳米钛酸钡，对纳米钛酸钡及其复合湿敏材料的红外光谱（IR）与光电子能谱（XPS）进行了分析和比较，复合材料的IR谱基本是钛酸钡和RMX的IR谱的结合。在XPS谱中，两类湿敏材料的O(ls）峰都是由晶格氧O1和吸附氧Oa两峰构成，复合材料的Oa/O1比大于纳米钛酸钡，在O(1s），Ba(3d）和Ti(2p）谱中，复合材料的主峰同纳米钛酸钡相比，向低结合能方向移动0.3-0.6eV，这是因为复合材料中纳米与有机材料边界区域的晶格结构产生畸变，使其结合能略有减弱。     

Effect of silane as coupling agent on the dielectric properties of BaTiO3-epoxy composites

The influence of silane coupling agents on the microstructure and dielectric behaviour of epoxy/BaTiO₃ composites was studied. Epoxy was diluted using tetrahydrofuran as solvent in order to facilitate the mixing step. Methoxy silane was applied onto ceramic particles. Different diluted aqueous solutions with 0.25, 0.35 and 0.50 wt% of silane/BaTiO₃ were used. Dipping technique was utilised to obtain composite films. Dielectric measurements were performed from 25 Hz to 1 MHz and from 20 °C to 120 °C. Composites presented good dielectric properties and a strong dependence with the silane concentration.     

Peculiar feature of KCl + SbCl3 phosphors: PL and XRD studies

Photoluminescence of antimony-activated potassium chloride prepared by a mechanical grinding method has been reported. The non-coincidence of the excitation and diffuse absorption band has been found as a result of the peculiar nature of the mixed phosphor, which suggests the different nature of the luminescent centers present in the phosphor. This difference in the nature of the diffuse absorption spectra and excitation spectra has been attributed to the Sb³⁺ and Sb⁵⁺ ions in the KCl+SbCl₃ host lattice. Photoluminescence intensity has been strongly enhanced by reducing the temperature to the liquid nitrogen temperature. The powder diffraction pattern obtained from the XRD analysis shows the presence of complexes over the surface.     

Dielectric,mechanical and thermal properties of polymer/BaTiO3 composites for embedded capacitor

Barium titanate (BaTiO₃) filled polymethylmethacrylate (PMMA) composites were prepared using the simple solution method followed by hot pressing. The content of BaTiO₃ was varied from 0 to 65 vol.%. Scanning electron microscopy showed good dispersion and adhesion of BaTiO₃ with the PMMA matrix. The dielectric constant of the composites increased significantly. There was weak dispersion in the dielectric constant of the composites (up to 45 vol.%) with frequency between 100 Hz and 15 MHz. The dissipation factor of the composites increased from 0.021 for pure PMMA to 0.029 for 45 vol.% composites. However, 65 vol.% composite showed dispersion in dielectric constant with increasing frequency and higher dissipation factor. The Lichtenecker equation agreed well with the experimental data. The microhardness and the glass transition temperature of the composites increased approximately 4.7-fold and 42 °C, respectively, compared to pure PMMA. The CTE of the 65 vol.% composite is close to that of copper.     

Mn-doped polycrystalline BaTiO3

Barium titanate was doped with ≲ 1 mol % Mn and sintered in air under conditions producing grain growth. Treatment at elevated temperatures in atmospheres of various oxygen partial pressures resulted in changes in crystallographic transition temperatures and in resistivity that seemed to be associated with a change in the valence state of manganese.