Improving dielectric properties of BaTiO₃/ferroelectric polymer composites by employing surface hydroxylated BaTiO₃ nanoparticles

Dielectric properties of poly(vinylidene fluoride) (PVDF) based nanocomposites filled with surface hydroxylated BaTiO(3) (h-BT) nanoparticles were reported. The h-BT fillers were prepared from crude BaTiO(3) (c-BT) in aqueous solution of H(2)O(2). Results showed that the dielectric properties of the h-BT/PVDF nanocomposites had weaker temperature and frequency dependences than that of c-BT/PVDF nanocomposites. Meanwhile, the h-BT/PVDF composites showed lower loss tangent and higher dielectric strength. It is suggested that the strong interaction between h-BT fillers and PVDF matrix is the main reason for the improved dielectric properties.     

聚偏氟乙烯-钛酸钡复合材料的介电性能

用钛酸酯和钛酸丁酯偶联剂对BaTiO₃粉进行表面处理,使用熔融法制备了BaTiO₃/PVDF复合材料薄片。通过疏水亲油实验定性地分析了钛酸酯和钛酸丁酯偶联剂对BaTiO₃粉的偶联作用,通过测定BaTiO₃/PVDF的介电常数和介电损耗角正切值表征了复合材料的介电性能,BaTiO₃/PVDF扫描电子显微镜(SEM)的微观形态分析发现,经过偶联剂表面处理,BaTiO₃粉在PVDF中的分散情况改善。     

微波法合成纳米BaTi03及其表征

以TiCl4和BaCl2为主要原料,用微波法一步成功合成纳米BaTiO3,采用X射线衍射谱（XRD）、扫描电镜（SEM）、漫反射吸收谱（DRS）、介电常数谱和热重一差热分析（TG-DTA）表征,XRD和SEM分析表明,合成的BaTiO3为纯的立方相纳米BaTiO3,颗粒大小均匀,分散性好,晶粒粒径在90nm左右;DRS和介电常数测试表明,纳米BaTiO3禁带宽度为3．4eV,具有良好的介电性能;TG-DTA和XRD测试表明,在400℃以前,纳米BaTiO3表面吸附的残余有机物质燃烧放热,有l-4％左右的热失重,对应在290℃左右有较强的放热峰;1000℃煅烧后才有部分立方相的BaTiO3转化成了四方相的BaTiO3,纳米BaTi03表现出了良好的热稳定性。     

BaTiO3/环氧高介电常数复合材料

以BaTiO3、CYD128型环氧树脂、丁腈橡胶和4,4-二氨基二苯基砜为原料,采用共混法制备了具有高介电常数和低介电损耗性能的BaTiO3/环氧复合材料.实验结果表明,环氧树脂中添加BaTiO3后,介电常数从4提高到25,介电损耗从0.4%提高到0.7%.丁腈橡胶的加入使复合材料的介电常数进一步提高到41,介电损耗提高到1.7%,体积电阻率降低到1×1011Ω,击穿强度保持在8kV/mm.Lichtenecker模型计算表明,环氧树脂中BaTiO3的有效介电常数为343,丁腈橡胶为138.     

PVDF/改性BaTiO3复合材料介电性能研究

用硅烷和钛酸酯偶联剂对BaTiO3粉进行了表面处理，使用溶剂法制备了PVDF／BaTiO3复合薄膜，通过疏水亲油实验定性地分析了硅烷和钛酸酯偶联剂对BaTiO3粉的偶联作用可以改善PVDF／BaTiO3的界面结合，通过测定PVDF／BaTiO3的介电常数和介电损耗角正切值表征了复合材料的介电性能，PVDF／BaTiO3扫描电子显微镜（SEM）的微观形态分析发现，经过偶联剂表面处理，BaTiO3粉在PVDF中的分散情况改善，偶联剂的用量对微观形态影响较大。     

BaTiO3纳米粒子/环氧精细功能复合材料的制备及其介电性能的研究

采用精细复合工艺, 制备了BaTiO₃纳米粒子/环氧复合材料, 研究了该复合材料的介电常数随BaTiO₃含量的变化关系, 以及复合材料的介电损耗性能。      

纳米钛酸钡掺杂聚酰亚胺基高介电复合薄膜的制备及性能

采用原位聚合法和高速砂磨法制备了纳米钛酸钡/聚酰亚胺高介电常数复合薄膜,分析了不同制备方法及钛酸钡粉体用量对复合薄膜结构和性能的影响。实验结果表明,高速砂磨法对于纳米钛酸钡粉体的分散效果优于原位分散法;钛酸钡粉体的引入,有效提高了复合薄膜的热稳定性和介电性能。当粉体的体积分数达到50%时,复合薄膜介电常数相较于纯膜提高了10倍,而介电损耗只有少量增加。     

纳米BaTiO3及其陶瓷材料的特殊物性的研究

报导了硬脂酸凝胶法制备的ＢａＴｉＯ３纳米晶及烧制的陶瓷材料的特殊物性，用Ｘ射线衍射、高分辨透射电镜、Ｘ荧光光谱、表面光电子能谱、介电谱、热释电谱研究了纳一粉及陶瓷材料的晶体结构，晶粒尺寸体相和表面相组份及铁电性能。结果表明，所有样品在室温下均为立方结构，没有铁电性，陶瓷样品在低温下具有铁电性。并发现纳米晶ＢａＴｉＯ３及陶瓷具有湿敏特性。     

BaTiO_3@Cu核-壳复合粒子电/磁双响应性能

以平均粒径约为500nm的BaTiO_3微球为基核,通过"一步法"成功地制备了BaTiO_3@Cu核-壳复合粒子。利用SEM、TEM、XPS、介电测量分析仪和阻抗分析仪等对复合粒子的组成、结构、介电性能和磁性能进行测定。另外将纯BaTiO_3和BaTiO_3@Cu核-壳复合粒子分别分散到水凝胶中,通过测量和分析在有/无电场、磁场和电磁复合场作用下得到的水凝胶的储能模量,考察粒子在水凝胶中的电、磁和电磁响应性能。结果表明,BaTiO_3@Cu复合粒子具有完整清晰的核-壳结构,在整个表面壳层铜元素中,Cu(0)的原子分数达到了90at%,具有优良的介电性能和磁性能。BaTiO_3@Cu核-壳复合粒子是一种对外加电场和磁场作用都具有响应性能的多功能新型智能材料,且其电磁复合响应性能显著强于纯BaTiO_3粒子。     

粒度对纳米掺杂BaTiO3陶瓷结构和性能的影响

制备了纳米掺杂BaTiO3陶瓷,研究了纳米掺杂剂和BaTiO3的粒度对BaTiO3陶瓷的微观结构和介电性能的影响．结果表明,小粒度、高分散的纳米掺杂剂更易对BaTiO3颗粒实现均匀包裹,有效地抑制晶粒生长并形成更多的壳-芯晶粒,大比表面积使更多高活性的表面原子与BaTiO3发生原子输运形成传质,导致晶粒壳／芯比增大,从而提高其介电性能．纳米掺杂陶瓷的平均晶粒尺寸和四方率与BaTiO3粒度几乎成正比．随着BaTiO3粒度的减小,立方晶粒壳增大而四方晶粒芯减小,陶瓷由四方晶相向赝立方晶相转变,居里峰被显著压制,从而改善介电温度特性．同时,晶粒的壳与芯之间失配产生的内应力随之增加,使居里点向高温方向移动．     

BaTiO3纳米粉体的制备和性能

采用溶胶-凝胶和溶胶-沉淀的方法合成了立方相纳米BaTiO3粉体．溶胶-凝胶法制备的粉体平均粒径为19nm，颗粒分布均匀、含少量BaCO3．溶胶-沉淀法得到了纯BaTiO3粉，平均粒径为42nm，存在部分团聚．两种方法相比，溶胶-凝胶法的粉体烧结密度较高，介电性能较好．讨论了两种合成方法的晶粒形成机理及对材料微观结构和介电性能的影响．     

纳米掺杂和直接掺杂Li2O-SiO2复合助烧剂对X7R型BaTiO3基陶瓷显微结构和介电性能的影响

以Li2O-SiO2（LSO）复合组分作为助烧剂,比较纳米掺杂和直接掺杂对X7R型BaTiO3基陶瓷显微结构和介电性能的影响,并进一步研究直接掺杂LSO的用量及烧结温度的影响,同时通过缺陷化学理论探讨了陶瓷的烧结机制。实验结果表明与纳米掺杂相比,直接掺杂助烧剂能够使掺杂元素进入晶格产生离子空位等缺陷,减少了物质迁移所需的活化能,从而有效促进陶瓷致密化过程,显著改善陶瓷的微观形貌及其介电性能。陶瓷样品的介电常数随着LSO助烧剂掺杂量的增加先增大后减小;当助烧剂掺杂量为0.08%（摩尔分数）时,样品可在1200℃烧结,室温介电常数达到4855,且容温特性满足X7R标准。通过直接掺杂能够使助烧剂十分均匀地分布在陶瓷材料中,可以显著减少助烧剂的用量,达到明显降低烧结温度的目的,并起到助烧兼改性的作用。     

添加助烧剂对CoFe_2O_4/BaTiO_3复相多铁材料性能的影响

采用固相合成法制备出尖晶石结构CoFe_2O_4粉末和钙钛矿结构BaTiO_3,并按照2∶8的摩尔比将粉末混合,随后添加不同的助烧剂。研究多种助烧剂对制备出的CoFe_2O_4/BaTiO_3复相多铁材料成分、微观形貌、介电性能、铁电性和磁性能的影响。结果表明:仅添加助烧剂Bi2O3,难以达到烧结致密的目的;当助烧剂中含有CaCO3-SiO2时,有效提高了CoFe_2O_4/BaTiO_3复相多铁材料的烧结性能,在相同的烧结温度下,CoFe_2O_4/BaTiO_3复相多铁材料致密度得到提升,且介电性能、铁电性、磁性能均有一定程度的优化。     

Terahertz response of ferroelectric nanofibers

Far-infrared optical and dielectric properties of ferroelectric SrTiO3 and BaTiO3 nanofibers, prepared by hydrothermal syntheses, were studied using terahertz time-domain spectroscopy. The power absorption, refractive index, and complex dielectric function were characterized in the frequency range from 0.2 to 1.0 THz. The measured results are well reproduced by theoretical fittings based on the dielectric models and the effective medium model. The study reveals that the low-frequency dielectric properties of the ferroelectric SrTiO3 nanofibers are associated with the lowest transverse optical (TO) soft mode TO1 at 2.70 THz (90.0 cm(-1)), and that of the ferroelectric BaTiO3 nanofibers are related to the lowest pair of transverse optical (TO) and longitudinal optical (LO) modes near 5.35 THz, which are both consistent with their bulk single-crystal and thin-film counterparts.     

Dielectric properties of Ni-coated BaTiO/sub 3-/PMMA composite

Dielectric properties of Ni-coated BaTiO(3)-PMMA (polymethyl methacrylate) composite were studied from an embedded capacitor application viewpoint. Volume loading of up to 50% was attempted, and the results were compared with uncoated BaTiO(3)-PMMA composite. Ni-coating on BaTiO(3) powder was found to greatly improve the dielectric properties of the composite, especially the dielectric constant value. K values of about 100 with temperature-stable X7E characteristics were realized.     

GISAXS analysis of 3D nanoparticle assemblies--effect of vertical nanoparticle ordering

We report on grazing-incidence small-angle x-ray scattering (GISAXS) study of 3D nanoparticle arrays prepared by two different methods from colloidal solutions-layer-by-layer Langmuir-Schaefer deposition and spontaneous self-assembling during the solvent evaporation. GISAXS results are evaluated within the distorted wave Born approximation (DWBA) considering the multiple scattering effects and employing a simplified multilayer model to reduce the computing time. In the model, particular layers are represented by nanoparticle chains where the positions of individual nanoparticles are generated following a model of cumulative disorder. The nanoparticle size dispersion is considered as well. Three model cases are distinguished-no shift between the neighboring chains (AA stacking), a shift equal to half of the mean interparticle distance (AB stacking) and random shift between the chains. The first two cases correspond to vertically correlated nanoparticle positions across different chains. A comparison of the experimental GISAXS patterns with the model cases enabled us to distinguish important differences between the 3D arrays prepared by the two methods. In particular, laterally ordered layers without vertical correlation of the nanoparticle positions were found in the nanoparticle multilayers prepared by the Langmuir-Schaefer method. On the other hand, the solvent evaporation under particular conditions produced highly ordered 3D nanoparticle assemblies where both laterally and vertically correlated nanoparticle positions were found.     

Dielectric investigations and theoretical calculations of size effect in lead titanate nanocrystals

The dielectric properties of nanograin ferroelectric lead titanate crystals are presented. The PbTiO3 samples were prepared by pressing nanopowders into plates and were studied experimentally by dielectric permittivity measurements in a wide frequency and temperature range. The TC dependence obtained showed a critical change of behavior with increasing mean nanoparticle size in the 9-nm region. The theoretical calculations based on Monte Carlo simulation were performed to describe the behavior of this material. It was shown that the distribution of nanoparticle sizes in the sample taken into account with the Monte Carlo method describes the dielectric properties of PbTiO3 nanocrystals quite well.     

Nanostructure patterns of piezoelectric and ferroelectric complex oxides with various shapes, obtained by natural lithography and pulsed laser deposition

A variety of patterns of well-ordered perovskite-type complex oxide nanostructures were obtained by pulsed laser deposition (PLD) on conductive single crystalline substrates through latex sphere monolayer and double-layer masks. Patterns obtained via deposition through hexagonally close packed (hcp) latex sphere monolayers include the usual arrays of hexagonally ordered nanoislands, hexagonal arrays of nanorings of much lower height coexisting with hexagonal nanoislands, hcp shell-like structures, and hexagonally interconnected nanocrown arrays. The formation of the nanopatterns depends on the ambient gas pressure during PLD, with well-separated nanoislands obtained at low pressures, and interconnected nanocrowns formed at high pressures. After annealing, the obtained BaTiO(3) and SrBi(2)Ta(2)O(9) nanopatterns were examined by piezoresponse force microscopy using conductive scanning probes. Under an external biasing electric field, polarization domain reversal was observed in the nanopatterns with deep submicron lateral dimensions. BaTiO(3) nanocrowns ～9?nm high are ferroelectric, while SrBi(2)Ta(2)O(9) nanorings of ～5?nm thickness show at least piezoelectric activity. In addition to the patterns of hexagonally ordered nanostructure arrays, a pattern of rhombohedrally ordered nanostructure arrays was also fabricated by deposition through latex sphere double layers.     

纳米Mg(OH)2-ZnO/聚酰亚胺复合薄膜的介电和热性能

采用反向沉淀法制备了Mg（OH）₂-ZnO纳米粒子,通过原位聚合和热亚胺化的方法成功制备了不同纳米Mg（OH）₂-ZnO粒子质量分数的纳米Mg（OH）₂-ZnO/聚酰亚胺（PI）复合薄膜,通过SEM、热重分析、介电谱测试仪和击穿场强测试仪对薄膜的表面形貌、热稳定性、介电性能和击穿强度进行表征和测试。结果表明：Mg（OH）₂-ZnO纳米粒子均匀地分散在PI基体中,Mg（OH）₂-ZnO/PI热稳定性下降,介电常数、介电损耗和电导率增加,击穿场强随纳米粒子增加先增加后减小,在纳米粒子含量为2%时,达到最大值296 kV/mm。     

Dielectric properties of ultrafine grained BaTiO(3)

The dielectric constant and spontaneous polarization of fine-grained BaTiO(3) prepared from powder produced by metalloorganic decomposition technology were studied. The room-temperature dielectric constant of BaTiO(3) was found to increase sharply with increase in grain size, reach a maximum at about 0.4 mum, and decrease with further increase in grain size. Spontaneous polarization continuously decreased with decrease in grain size. A model is proposed to explain the grain size dependence of the dielectric constant.