纤维钛酸钡与纳米钛酸铅和氧化锆的复合烧结及物相分析

纤维状钛酸钡具有高度单轴定向性,纳米粉钛酸铅具有高比表面积、高活性。本文将纤维钛酸钒与纳米钛酸铅、氧化锆复合,利用纤维定向和纳米添隙及活性制备新型功能陶瓷锆复合,利用纤维定向和纳米添隙及活性制备新型功能陶瓷通过ＸＲＤ、ＳＥＭ等分析方法对材料的物相组成和显微结构进行分析,结果表明纳米粉与纤维发生固溶,使主晶相钛酸钒纤维的晶面间距发生改变,但纤维的定向性仍然存在。     

钛酸铋铁电薄膜的改性及其复合薄膜的磁电耦合效应研究

对铋层状钙钛矿结构钛酸铋无铅铁电薄膜的制备、改性、失效行为,以及钛酸铋-铁酸钴多铁复合材料进行了研究。通过分析A位和B位离子的极化率和半径关系,设计了一系列复合掺杂钛酸铋基无铅铋层状钙钛矿铁电体系,并制备出了一系列性能优良的单掺杂和复合掺杂的钛酸铋基无铅铁电薄膜,结果表明A位La~(3 )、Nd~(3 )、Eu~(3 )掺杂,B位V~(5 )、Zr~(4 )、Mn~(4 )都可以明显提高薄膜的性能,特别是A位Nd~(3 )掺杂可以很好地提高剩余极化强度和抗疲劳性,B位Mn~(4 )掺杂可以降低矫顽场和漏电电流,有望突破无铅铁电薄膜的应用瓶颈;同时,研究了铁电薄膜及其在辐照条件下的疲劳、保持性能损失和印记失效等失效行为,提出了一个能合理解释印记失效的双界面层的理论模型;还利用化学溶液沉积法制备了不同复合结构(颗粒复合和层状复合)的Nd掺杂钛酸铋/铁酸钴多铁薄膜,并研究了不同复合结构中的磁电耦合效应,研究发现在铁电/铁磁多铁复合材料中,铁电/铁磁界面处两种不同材料之间的原子相互耦合对磁电耦合效应具有很大的贡献。     

锆钛酸铅铁电薄膜的制备及性能研究

本文用无机锆盐代替锆的醇盐，研究了溶胶－凝胶技术制备锆钛酸铅（简称ＰＺＴ）铁电薄膜的热处理工艺、结构和电性能。研究结果表明，在Ｓｉ单晶基片上制备的ＰＺＴ薄膜为钙钛矿型结构的陶瓷薄膜，其晶粒细小、致密，且具有良好的铁电性能，适合于制备铁电存贮器。     

扩散阻挡法制备铁酸钴/锆钛酸铅0-3复合材料及性能研究

通过溶胶-凝胶工艺在铁酸钴(CoFe2O4,CFO)陶瓷粉体表面包覆二氧化锆,形成核壳结构。以钨酸锂Li2WO3作为铁电相锆钛酸铅镧(PLZT)的烧结助剂以降低烧结温度。将两种粉体混匀,经成型和共烧工艺制备了xCFO/(1-x)PLZT 0-3复合多铁性陶瓷(质量分数x为0.1、0.2、0.3、0.4)。研究了铁磁相含量、陶瓷的晶相结构、微观形貌以及烧结工艺条件对陶瓷介电、压电、铁电性能的影响。X射线衍射分析表明,复合多铁性陶瓷样品保持了较纯净的钙钛矿(PLZT)和尖晶石(CoFe2O4)结构。扫描电镜形貌分析和能谱分析显示复合材料的两相分布均匀,氧化锆成功包覆在铁磁相CoFeO4颗粒表面,且二氧化锆大大减少了高温下铁、钴离子的扩散。当磁场频率为10kHz时,1100℃烧结的CFO/PLZT复合陶瓷(x=0.2)的磁电转换系数约为3.53×106mV/(T.cm)。     

高掺银-钛酸铅复相薄膜的制备研究

采用溶胶-凝胶法, 通过在新鲜溶胶和在陈化溶胶中分别高掺银这两种制备工艺过程, 制备了分散均匀的立方相银颗粒-钛酸铅相基质复相薄膜. 利用XRD, SEM, TEM等方法对先驱体溶胶和薄膜的组成与结构进行了测试. 研究表明, 溶胶中Ag的存在形式直接对薄膜的晶相形成过程产生影响. 当银以Ag⁺的形式存在于溶胶中时, 银优先消耗部分铅析出银-铅合金相, 体系含银量较少时形成焦绿石相钛酸铅, 含银量较多时, 形成固溶有银的钙钛矿相钛酸铅; 当银以银团簇的形式存在于溶胶中时, 薄膜中直接形成钙钛矿相钛酸铅晶相.     

锰掺杂对PMN-PZT陶瓷介电性能的影响

研究了锰掺杂对富锆PMN-PZT（铌镁酸铅一锆钛酸铅）陶瓷材料的相组成、微观结构、介电性能等方面的影响，并对实验结果作出物理机理的解释。实验结果表明：适量的锰掺杂有助于陶瓷晶粒的生长，并能有效地降低PMN-PZT陶瓷材料的介电常数和介电损耗，在锰掺杂量为3．0％（原子分数）时，εr：197、tanδ=0．15％，作为用于红外热释电探测器的陶瓷材料具有良好的介电性能。     

铟掺杂PZT铁电陶瓷性能研究

采用传统固相烧结法制备In2O3掺杂的锆钛酸铅(PZT)铁电陶瓷,研究了In2O3掺杂量对PZT铁电陶瓷材料的相组成、微观结构、介电性能、压电性能及铁电性能的影响。研究结果表明,随着In2O3掺杂量的增加,PZT材料在准同型相界处三方相增加四方相减少,适量掺入In2O3有利于晶粒均匀生长。在不同的铟掺杂剂量下,PZT陶瓷材料分别具有最佳的铁电及压电性能。当铟掺杂量为0.1%(质量分数)时,PZT材料具有最佳的铁电性能,其剩余极化强度为23.43μC/cm2,矫顽场为9.783kV/cm。当铟掺杂量为0.3%(质量分数)时,PZT材料具有最好的压电性能,其tanδ=0.023,d33=540pC/N,εr=1513,Kp=0.764,Qm=1819。     

钕掺杂锆钛酸铅纳米粉体的溶胶-凝胶法合成研究

以乙二醇为溶剂,硝酸钕为钕源,采用改进的溶胶-凝胶法制备了钕掺杂锆钛酸铅纳米粉体Pb1-3x/2NdxZr0.52Ti0.48O3(PNZT).通过FTIR、XRD、TG-DTA讨论了溶胶经热处理制备纳米粉体的反应机理,PNZT的热处理温度较PZT高50～100℃.采用XRD、SEM、TEM对纳米粉体进行表征.研究表明,钕掺杂增加了晶格畸变程度.与PZT相比,随着钕掺杂量增加晶格参数a和V下降,而参数c和c/a则不同,少量钕掺杂导致参数c和c/a增加,随着钕掺杂量增加逐渐下降.当钕掺杂量≤9%(摩尔分数)时可生成粒径约为20～50nm的钙钛矿型粉体, Nd3 离子取代Pb2 离子与Ti4 离子、O2 离子形成稳定的钙钛矿型结构.     

Co掺杂GaFeO3陶瓷的结构、导电及磁性能研究

GaFeO₃因其磁电耦合效应成为目前极具潜质的多铁性材料之一。本工作采用固相烧结法制备了不同钴掺杂浓度的铁酸镓陶瓷,并研究了钴的掺杂浓度对铁酸镓陶瓷的相组成,微观结构形貌,漏电流及磁性的影响。XRD及Rietveld精修结果显示除了主相GaFeO₃,还存在第二相,且随着钴含量的增加,第二相含量逐渐增加,晶体的畸变程度增大;因为掺入二价阳离子Co²⁺并引入了第二相,样品的漏电性能和纯GaFeO₃陶瓷相比显著改善;当钴掺杂浓度为2at%时,样品的漏电流密度相较于GaFeO₃降低了7个数量级;掺入Co²⁺引入第二相且晶格畸变程度增加使得GaFeO₃的磁性增强。研究结果表明:铁酸镓中掺杂微量的钴可以改善磁性,并使漏电流大幅降低而磁转变温度无明显下降。     

原位Raman光谱技术研究PLZT铁电陶瓷相变

采用传统固相反应法制备了原子比Zr/Ti≈52/48,掺杂少量镧的锆钛酸铅(PLZT)铁电陶瓷材料,X射线衍射分析表明得到的陶瓷粉末样品为纯钙钛矿相。对PLZT铁电陶瓷材料进行不同温度下的原位Raman谱观测,得到了各Raman特征谱的频率和峰强随温度的变化规律。结果表明,从-200℃升温至600℃过程中,准同型相界附近的PLZT铁电陶瓷分别发生了两种相变:在0℃发生了单斜相到四方相的转变,而在350℃发生了四方相到立方相的转变;并且,在-150℃和250℃附近还可能分别发生低温单斜相到高温单斜相和混合相的相变。     

Electric and magnetic properties of Pb(Zr0.52Ti0.48)O3-CoFe2O4 particle composite thin film on the SrTiO3 substrate

We deposited a thin epitaxial Pb(Zr_0.52Ti_0.48)O₃ (PZT) layer on the (0 0 1) SrTiO₃ (STO) substrate doped with Nb (0.5 wt.%), then grew composite thin film of CoFe₂O₄ (CFO) and PZT phases on it. X-ray diffraction and high resolution transmission electron microscopy showed that the PZT and CFO phases in the film had perfect epitaxial structures. CFO nanoparticles were embedded in PZT matrix randomly, which was useful to enhance the insulativity of the composite film. The composite thin film exhibited good ferromagnetic and ferroelectric properties. The dielectric constants of the composite thin film kept unchangeable in a wide bias electric field, but increased in a magnetic field, namely, magnetodielectric effect. The possible reasons for the magnetodielectric effect were discussed.     

Microstructures, ferromagnetic, and ferroelectric properties in polyvinylpyrrolidone-assisted CoFe2O4/Pb(Zr0.53Ti0.47)O3 multiferroic composite thick films

CoFe₂O₄/Pb(Zr_0.53Ti_0.47)O₃ (CFO/PZT) multiferroic composite thick films with different CFO mass fractions have been prepared onto Pt/Ti/SiO₂/Si substrate by a hybrid sol–gel process and spin coating technique. Polyvinylpyrrolidone (PVP) was employed to be an assistance to the sol–gel solution for enhancing the film thickness and promising a crack-free film surface. After annealing at 650 °C in air for 1 h, phase structure, microstructure, magnetic and ferroelectric properties as well as leakage current of multiferroic thick films were investigated. X-ray diffraction indicated a deeply buried distribution of CFO particles in the PZT matrix. Scanning electronic microscopes showed crack-free surfaces and a decreasing film thickness from 7.2 μm to 6.2 μm with increasing CFO content. Furthermore, the saturated magnetization and remanent magnetization were also hence increased. In addition, mass fraction of CFO in PZT matrix was also estimated from 0.36% to 4.58% according to the relationship between M _s and magnetic content. Ferroelectric hysteresis loops revealed saturated polarization (P _s) and remanent polarization (P _r) were diluted by CFO till its mass fraction rising to 1.8%. After that, polarization was increased with further increasing CFO content. Enhanced leakage was demonstrated to be partially contributed to them. A critical content of 1.8% was hence confirmed, where ferroelectric and magnetic properties can be balanced, indicating a possible stress-transferred magnetoelectric coupling effect in this composite.     

The effect of acetic acid on morphology of PZT nanofibers fabricated by electrospinning

Lead zirconate titanate (PZT)/poly vinyl acetate (PVAc) green nanofibers were spun by electrospinning PZT/PVAc mixture. The acidification (acetic acid) effect of PZT/PVAc solution on the morphology of PZT ceramic fibers calcined at various temperatures was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) and X-ray diffraction (XRD). The PZT ceramic fibers processed with acetic acid (CH₃COOH) turned out to be thinner and more compact, compared to the fiber without it. It was also evident that there was an optimal concentration of acetic acid for the dense PZT nanofiber. In addition, FTIR and XRD revealed that the complete perovskite formation was achieved by the calcination between 650 °C and 700 °C.     

纳米颗粒磁增强SBA-15介孔复合材料的制备及磁性能

利用浸渍法合成了Co₃O₄/SBA-15和CoFe₂O₄/SBA-15介孔纳米磁性材料, 并利用X射线粉末衍射(XRD)、 透射电子显微镜(TEM)、 场发射扫描电子显微镜(FESEM)及振动样品磁强计(VSM)对样品的微观结构和磁性能进行了分析。结果显示, Co₃O₄及CoFe₂O₄纳米颗粒分布在SBA-15介孔材料的孔道中, 可有效提高SBA-15介孔材料的磁性能。研究发现, SBA-15介孔纳米磁性材料的磁特性由掺杂的纳米磁性颗粒的性质决定, 其磁性能随Co₃O₄及CoFe₂O₄含量的增加而升高, 矫顽力可达400Oe, 饱和磁化强度达9emu/g。      

Enhancement of the visible-light photocatalytic activity of In2O3-TiO2 nanofiber heteroarchitectures

One-dimensional In(2)O(3)-TiO(2) heteroarchitectures with high visible-light photocatalytic activity have been successfully obtained by a simple combination of electrospinning technique and solvothermal process. The as-obtained products were characterized by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-vis spectra. The results revealed that the secondary In(2)O(3) nanostructures were successfully grown on the primary TiO(2) nanofibers substrates. Compared with the pure TiO(2) nanofibers, the obtained In(2)O(3)-TiO(2) heteroarchitectures showed enhancement of the visible-light photocatalytic activity to degrade rhodamine B (RB) because of the formation of heteroarchitectures, which might improve the separation of photogenerated electrons and holes derived from the coupling effect of TiO(2) and In(2)O(3) heteroarchitectures. Moreover, the In(2)O(3)-TiO(2) heteroarchitectures could be easily recycled without the decrease in the photocatalytic activity because of their one-dimensional nanostructural property.     

Modified room‐temperature magnetic and optical properties in bilayer xBi6Fe2Ti3O18 − (1−x)CoFe2O4 composite thin films

Heterogeneous bilayer of Aurivillius compound Bi₆Fe₂Ti₃O₁₈ (BFTO) and Cubic spinel structure CoFe₂O₄ (CFO), a class of highly effective multiferroic composites, have been synthesized on fused quartz substrate by sol–gel method. Both BFTO and CFO layers are synthesized separately without any chemical reaction which can be confirmed by XRD pattern and Raman spectroscopy for two individual sets of maps. SEM and AFM images also verify two separate layers by showing the boundary between two layers clearly. Furthermore, linear increased ferromagnetism with increasing CFO component has been detected, further proving the independence of BFTO and CFO phases. Non-linear changed electron transition energy has been observed which may be derived from the crystal field distortion at the interface of the two layers. Therefore, an appropriate component can be found which have both excellent magnetic and optical properties, showing great potential on solar-energy conversion devices and multiferroic applications. In addition, variable temperature transmission spectra have been detected and the results are worth to be analyzed deeply.

     

Enhanced magnetoelectric coupling in Pb(Zr0.52Ti0.48)O3 film-on-CoFe2O4 bulk ceramic composite with LaNiO3 bottom electrode

By chemically depositing a conductive LaNiO₃ (LNO) electrode layer onto dense CoFe₂O₄ (CFO) ceramics, the magnetoelectric (ME) response in Pb(Zr_0.52Ti_0.48)O₃ (PZT)/CFO film-on-substrate system was significantly enhanced. Structural, morphological, ferroelectric, and piezoelectric analysis was performed for the present PZT/LNO/CFO film-electrode-substrate composites, whereby improved electric-related output was demonstrated. It was further shown that the maximum ME coefficient α _E31 could reach up to 155 mV/cm Oe, which was about 2.6 times higher than that in PZT film-on-CFO ceramics without bottom electrode layer. Further enhancement of ME response could be expected by preparing high-quality electrode layer with optimal thickness and improved fabrication processing for such film-electrode-substrate composites.     

Processing and characterization of carbon nanofiber/syndiotactic polystyrene composites in the absence and presence of liquid crystalline polymer

Syndiotactic polystyrene (s-PS)/carbon nanofiber (CNF) composites were developed through melt process in a brabender mixer and then compression moulded. Thermal properties were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), while morphologies of the composites were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The degree of polymer and nanofiber alignment was assessed using X-ray diffraction. The resistivity reduced with increase in loading of carbon nanofibers. Surface modification of the carbon nanofiber resulted in improved properties compared to as-received carbon nanofiber composites.Blending of liquid crystalline polymer (LCP A950) with s-PS/CNFs developed composites results in improved electrical and thermal properties. This improvement is ascribed to the self reinforcing tendency of LCPs due to their rigid rod-like molecular structure, which helps to concentrate and align the carbon nanofibers.     

In-situ One-pot Preparation of LiFePO4/Carbon-Nanofibers Composites and Their Electrochemical Performance

A novel in-situ route was employed to synthesize LiFePO4/carbon-nanofibers (CNFs) composites. The route combined high-temperature solid phase reaction with chemical vapor deposition (CVD) using Fe2O3 and LiH2PO4 as the precursors for LiFePO4 growth and acetylene (C2H2) as the carbon source for CNFs growth. The composites were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) specific surface area, field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The electrochemical performance of the composites was studied by galvanostatic cycling and cyclic voltammetry (CV). The results showed that the in-situ CNFs growth could be realized by the catalytic effect of the Fe2O3 precursor. The sample after 80 min CVD reaction showed the best electrochemical performance, indicating a promising application in high-power Li-ion batteries.     

Experimental evidence of enhanced ferroelectricity in Ca doped BiFeO3

Calcium (Ca)-doped bismuth ferrite (BiFeO₃) thin films prepared by using the polymeric precursor method (PPM) were characterized by X-ray diffraction (XRD), field emission gun scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), polarization and piezoelectric measurements. Structural studies by XRD and TEM reveal the co-existence of distorted rhombohedral and tetragonal phases in the highest doped BiFeO₃ where enhanced ferroelectric and piezoelectric properties are produced by internal strain. Resistive switching is observed in BFO and Ca-doped BFO which are affected by the barrier contact and work function of multiferroic materials and Pt electrodes. A high coercive field in the hysteresis loop is observed for the BiFeO₃ film. Piezoelectric properties are improved in the highest Ca-doped sample due to changes in the crystal structure of BFO for a primitive cubic perovskite lattice with four-fold symmetry and a large tetragonal distortion within the crystal domain. This observation introduces magnetoelectronics at room temperature by combining electronic conduction with electric and magnetic degrees of freedom which are already present in the multiferroic BiFeO₃.