超细PbTiO3的工艺研究

通过PbTiO3合成的工艺研究,得出合成PbTiO3的最佳的工艺条件为:Pb(NO3)2:H2TiO3:NH4HCO3=1:1:2.1;沉淀反应的时间为30min,反应的温度为常温,反应后继续搅拌的时间为15min;煅烧的时间为2.5 h,煅烧的温度为500℃。     

Template-assisted electrodeposited cupric oxide nanotubes and hierarchical nanospikes for tailoring electrode-electrolyte interfacial charge transfer

Morphological modification in materials aids multi-channel electron access sites for easier electrolyte ion access for many electrochemical devices including energy storage devices. Controlled synthesis of such multichannel morphologies of metal oxides offers significant challenges. Herein, we report a template-assisted electrodeposition technique for the synthesis of Cu nanowires, which are transformed into either CuO nanotubes by controlled annealing or CuO hierarchical nanospikes using a simple hydroxyl ion impregnation technique and subsequent annealing. These materials are tested as electrodes in charge storage systems in 6 M KOH electrolyte in a three-electrode system; both electrodes have shown battery-type charge storage behaviour. Despite the chemical similarity between the two materials, the CuO nanospikes electrodes showed improved charge transport between electrode-electrolyte interface compared to the CuO nanotubes. With the cost-effectiveness, easy availability, and multi-channel morphology of CuO nanospikes along with the promising performance of the electrode in a three-electrode system, the present research offers future potential in developing low cost and high performing energy storage devices.     

Template-assisted hydrothermal synthesis and photocatalytic activity of novel TiO2 hollow nanostructures

TiO₂ hollow nanostructures were successfully synthesized by a controlled hydrothermal precipitation reaction using Resorcinol–Formaldehyde resin spheres as templates in aqueous solution, and then removal of the RF resins spheres by calcination in air at 450 °C for 4 h. The obtained TiO₂ hollow spheres were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N₂ adsorption–desorption analysis, and UV–visible diffuse reflectance spectroscopy. The photocatalytic activity of the as-prepared samples was evaluated by photocatalytic decolorization of rhodamine B aqueous solution at ambient temperature under UV illumination. The results indicated TiO₂ hollow nanostructures exhibit the excellent photocatalytic activity probably due to the unique hollow micro-architectures.     

Slow crystallization process from amorphous PbTiO3

The effect of isothermal annealing of amorphous PbTiO₃ at a temperature below the crystallization temperature, T_crys, has been investigated. Time dependent dielectric constant in the annealing process has been observed. From the experimental results, both the existence of the glass transition temperature, T_g, and the steadiness of dielectric constant at room temperature have been established.     

Template-assisted assembly of electrospun fibers

Ordinarily, the electrospinning process generates one-dimensional fibers which assemble into non-woven membrane structures due to instabilities in the fluid jet. In this paper, an electrospinning procedure is developed that utilizes patterned collectors to produce aligned membranes with designed topological structures. The template-assisted electrospinning approach is demonstrated using polycaprolactone (PCL) fibers to produce patterns including alphanumeric characters and a printed electronic circuit chip, with feature sizes on the order of several hundred microns. The process has a significant impact on micro-manufacturing, and provides the capability for incorporation of oriented fiber materials in patterned micro-composites and electronic components.     

Template-assisted syntheses of porous metal methylphosphonates

Neutral dibutyl methylphosphonate (DBMP) is used as a template to prepare porous metal methylphosphonates (metal = aluminum, titanium, zirconium). The removal of DBMP in the as-synthesized materials could be easily achieved by evaporation under vacuum without destroying the hybrid structure, as evidenced by elemental analyses, FT-IR spectra, ¹³C CP/MAS NMR and nitrogen adsorption-desorption isotherms. Thermal analyses show that three porous hybrid samples have high thermal stability in air. The exothermic weight losses due to oxidation combustion of organic species occluded in samples appear after 730 K. Furthermore, the templating effect of DBMP is also confirmed by comparing the hybrid materials synthesized in the presence or the absence of the template.     

Preparation and microstructure analysis of Fe-doped PbTiO3 ceramic

Fe-doped PbTiO₃ (PT) powder and bulk materials were prepared successfully by sol-gel technique and a subsequent sintering process using Fe (C₅H₅)₂ as a dopant agent. The effects of pH and temperature on the Fe-doped PT system were investigated. Thermogravimetry/differential thermal analysis (TG/DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the composition and the microstructure of the PT ceramics. The results indicated that the thermal decomposition of xerogel included three stages: volatilization of adsorption water and organic composition, oxygenolysis of n-butyl and acetate, and transformation of the crystalline phase. Well-stabilized collosol and gel could be obtained at 60°C and pH = 4.5. It was found that PbTiO₃, PbFe₂O₄, and TiO₂ crystalline appeared in the Fe-doped PT system when the mass fraction of the dopant Fe was 0.03%. Furthermore, from STM analysis, it could be seen that the grain size of doped PT ceramics was homogeneous and about 1–2 μm, and the pore of the PT ceramic was small. As a result, the PT ceramic had high tightness. __________ Translated from Journal of Harbin Institute of Technology, 2007, 39 (1): 165–168 [译自: 哈尔滨工业大学学报]     

四方相钛酸铅陶瓷的制备及表征

为了获得致密的钛酸铅陶瓷,用水热法合成的纯四方相钛酸铅纳米晶作粉体原料,采用传统方法,在不同氛围和温度下进行烧结.经X射线衍射(XRD)和扫描电子显微镜(SEM)分析,发现当以纯钛酸铅纳米晶作粉体原料时,即使采用传统烧结方法也可获得结构致密的纯四方相钛酸铅陶瓷,且敞口未粉埋的烧结氛围有利于陶瓷的致密化;烧结过程基本不存在氧化铅的挥发;烧结温度对钛酸铅的生长形态具有决定作用,烧结温度不同钛酸铅晶体的生长形态不同;在烧结过程中钛酸铅晶粒呈层状生长.     

Phase transition of nanophase ferroelectric PbTiO3 ultrafine powders

In this paper, ferroelectric PbTiO³ (PT) ultrafine powders with nanosized grains are prepared through sol-gel and hydrolysis-aging process. The lattice constants and grain size are determined by XRD analysis. The phase transition is examined by DSC and Second Harmonic Generation (SHG) measurements. The relation between onset temperature of phase transition and grain size is obtained. Results indicate that the phase transition of nanosized PT powder is broadened. The mechanism of broadened phase transition is discussed.     

Fabrication and topchemical transformation mechanism of PbTiO3 microplatelets

Two-dimensional platelets of the perovskite-structured PbTiO₃ were synthesized from a layer-structured PbBi₄Ti₄O₁₅ precursor, using a topochemical microcrystal route. The PbBi₄Ti₄O₁₅ precursor showed a high aspect ratio with an average size of ～7.74 μm and thickness of ～0.29 nm. Later, PbTiO₃ platelets coexisting with Pb₄Bi₄Ti₇O₂₄ mesophase were obtained, which had a more stable Aurivillius structure and was difficult to completely convert to the perovskite structure during topochemical microcrystal conversion. The reason that the Pb₄Bi₄Ti₇O₂₄ mesophase coexisted in PbTiO₃ platelets was deeply discussed. Both the crystal structure difference between the unit cell parameters for (Pb₄Bi₂Ti₇O₂₂)^2- and the thickness for the (Bi₂O₂)²⁺ layer, and the stability of (Bi₂O₂)²⁺ layer were used to analyze the existence of Pb₄Bi₄Ti₇O₂₄ phase. However, the result showed that the stability of (Bi₂O₂)²⁺ layer was the dominant reason, because the [OBi₄]/[OPb₄] tetrahedron formed in the (Bi₂O₂)²⁺ layer due to the similar chemical properties of Pb²⁺ and Bi³⁺. The work provided deep theoretical guidance to fabricate anisotropic perovskite platform-based topchemical microcrystal conversion mechanisms.     

Controlled synthesis of pointed carbon nanotubes

To fully realize the potential for the many applications of carbon nanotubes, it is necessary to control their morphology at will. Here we describe the controlled synthesis, on the fibers of a carbon paper, of multi-walled carbon nanotubes having either a regular cylindrical morphology or a novel morphology consisting of nanometric cylindrical tubes terminated by pointed tips about 0.5-1 μm long. Reshaping of the Ni-Co catalyst particle during the growth process has been directly observed for both regular and pointed nanotubes. However, total liquefaction of the catalyst particle is only observed during the growth of pointed tubes. Regular tubes result from the spiral scrolling of a graphene sheet resulting in a herringbone texture, while the tip of the pointed tubes displays a concentric textural character. The change in growth mechanism seems to occur upon total liquefaction of the catalyst.     

A new method to deagglomeration of PbTiO3 ultrafine powders

An innovative method for deagglomeration of ultrafine powders was developed in this paper. The method was based on electrohydraulic forces produced by electric breakdown discharge between two electrodes submerged in liquid. By controlling the process parameters (voltage, electrode separation and reaction time), PbTiO₃ ultrafine powders with spherical, tabular and aciculate shape were successfully deagglomerated. Two ways based on centrifugal sedimentation and laser-light scattering were used to determine the particle size distribution. Scanning electron microscope (SEM) images showed that the agglomeration of PT powders was greatly reduced.     

Elastic and piezoelectric properties of PbTiO3 at room temperature

We have calculated the phonon dispersion curves of lead titanate (PbTiO₃) at room temperature. A lattice dynamical formalism using the shell model is used. This microscopic model includes the short-range interactions of axially symmetric type and the long-range Coulomb interactions and taking into account of the electronic polarizability of constituent ions. Zone center phonon and a few phonons in the first Brillouin zone are used for fitting. In general, we obtain the best agreement between the calculated and observed frequencies. The values of relevant parameters are critically analyzed. A calculation of the elastic and piezoelectric properties is presented and compared with the available experimental data.     

溶胶-凝胶法制备超细PbTiO3铁电粉体

本文应用溶胶-凝胶法成功合成了超细钛酸铅(PbTiO3)粉体。经350℃预热处理1h,然后分别在700℃和800℃烧成并保温2h。试样XRD和AFM分析表明,试验获得纯的四方结构的粉体,粉体的平均粒子尺寸分别为30.0nm和30.9nm,c/a比分别为1.061和1.062,粉体的粘连度很小。     

Nanostructuring Effects in Piezoelectric BiScO3–PbTiO3 Ceramics

The apparent contradiction between the persistence of the polar state in morphotropic phase boundary BiScO₃–PbTiO₃ at the nanoscale, and the vanishing of the macroscopic ferroelectric switching and of the dielectric anomaly associated with the ferroelectric phase transition in nanostructured ceramics is solved. Raman spectroscopy results unambiguously demonstrate that the same polar phase exists in coarse grained and nanostructured materials. Soft modes were identified and followed upon heating, which allowed transition temperatures to be estimated. A shift of only 60°C was established as the size effect down to 24 nm average sized grains. Impedance spectroscopy was used to separate grain and boundary contributions to the total electrical response. Results clearly show grain boundaries to fully dominate this response in the case of nanostructured materials, which was responsible for the vanishing of the dielectric anomaly and for a large increase in the effective coercivity, the latter resulting in the loss of functionality. This was therefore a boundary effect, liable of being recovered by boundary tailoring. Indeed, macroscopic ferroelectricity was readily uncovered when grain‐boundary density was reduced by triggering grain growth.     

静电雾化沉积制备PbTiO3薄膜的研究

采用静电雾化沉积技术制备了PbTiO3薄膜,探索了沉积温度和沉积时间对所制备薄膜的结构和形貌的影响.通过调节制备工艺,制备了多孔和致密的PbTiO3薄膜.测试了所制备钛酸铅薄膜的介电频率特性,在100kHz的介电常数和介电损耗分别为222和0.0247.     

Easy synthesis of carbon nanotubes with polypyrrole nanotubes as the carbon precursor

An easy synthesis route for carbon nanotubes with polypyrrole nanotubes as a carbon precursor has been developed. Polypyrrole nanotubes were fabricated via a reactive self-degraded template method. Carbon nanotubes were further obtained by pyrolysis of the polypyrrole nanotube at 900 °C under a nitrogen atmosphere. The resultant carbon nanotube structure was found to be amorphous carbon on the basis of XRD, Raman spectra and high-resolution transmission electron microscopy (HRTEM) studies.     

火焰法制备碳纳米管研究进展

火焰法是近20年来兴起的一种新颖、高能效、低成本的碳纳米管制备方法。火焰法能同时提供制备碳纳米管所需的碳源和热源,具有大规模制备碳纳米管的潜力。由于火焰中环境极其复杂,控制火焰中碳纳米管的合成仍是巨大的挑战。本工作介绍了碳纳米管的结构及其性能,综述了扩散火焰(同轴扩散火焰、反扩散火焰和对冲扩散火焰)和预混火焰(单面滞止火焰和双面滞止火焰)制备碳纳米管的研究进展,并对碳纳米管的vapor–liquid–solid、顶部和底部及空心和实心生长机理作了简要阐述,介绍了本课题组基于甲烷/空气同轴射流火焰制备碳纳米管的研究进展。分析表明,金属镍起催化作用,催化剂颗粒包覆在碳纳米管内部,火焰合成的碳纳米管基于vapor–liquid–solid生长机制,碳纳米管直径为50~90 nm,平均直径为65 nm。对火焰法制备碳纳米管的发展方向进行了展望。