Fabrication and optical properties of two‐dimensional photonic crystal of ZnO pillars

Two‐dimensional (2D) photonic crystal of ZnO pillars was synthesized on silicon substrate by the combination of template method and vapor‐phase transport method. The microstructure and morphology of the ZnO photonic crystal was evaluated by using scanning electron microscope (SEM) and X‐ray diffraction (XRD). Large‐area specular reflectance measurements showed the presence of photonic stop band. The effect of the photonic band gap and the special structure on the photoluminescence (PL) properties of ZnO photonic crystal has been investigated. Both suppression and enhancement in the PL were observed. Raman scattering analyses demonstrated that the defect of ZnO photonic crystal exists in this experiment. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simple extraction‐solvothermal synthesis of single‐crystalline silver microplates

Single‐crystalline silver microplates, with average edge length of about 1.5 μm and thickness of 100 nm, have been synthesized by a simple extraction‐solvothermal method. Samples were characterized in detail by X‐ray diffraction (XRD), field‐emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM) and High‐resolution transmission electron microscopy (HRTEM) technologies. Extractant primary amine N1923 can also act as reducing agent. It has been found that microstructure of the silver can be controlled by the n‐octanol during the solvothermal treatment. Based on a series of experimental analysis, the possible formation mechanism of these microplates was discussed briefly. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of magnesium doped lead titanate

Magnesium (Mg) doped lead titanate powders (PT: Mg) ceramics, with various Mg contents (0, 2.5, 5, 7.5, 10, 12.5, 15, 17.5, 20, and 30 mole %), are prepared by the sol‐gel method and characterized by X‐Ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. XRD results show that the magnesium diminishes the lattice tetragonality of PT:Mg. The average particle size and morphology were studied by SEM. The investigations done by Raman spectroscopy allow the analyzis of the substitution mechanism behavior related to the Mg incorporation into PT structure. A concentration threshold appears around 10% of Mg corresponding in a change of the compensation process with Mg²⁺ ions replacing Pb²⁺ ions below and both Pb²⁺ and Ti⁴⁺ above. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of highly ordered hBN in presence of group I/IIA carbonates by solid state reaction

This comprehensive study declares experimentally the effects of IA/IIA metal carbonates on the formation of hexagonal boron nitride (hBN) with the aid of the available experimental methods as regards Fourier transform infrared spectroscopy (FT‐IR), powder X‐ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (TEM). hBN is synthesized in the existence of the metal carbonates at the low temperature by modified O'Connor method. The experimental findings of FT‐IR and XRD investigations show that the addition of metal carbonates affects considerably the crystallization of hBN powder during the synthesis process. The presence of the high concentration level of the additions improves harshly the crystallinity. In this respect, the graphitization index deduced from the XRD patterns reduces with the enhancement in the amount of the dopant content. At the same time, the differentiation between the products is analyzed by the SEM surveys. According to the results, the materials synthesized by the Li₂CO₃ powder exhibit both the tubular form and rod‐like while the other samples prepared by the CaCO₃ chemical dopant display the homogeneous plates. Even, the TEM images confirm the nanowires and nanotubes structures such as multi‐walled cylindrical, bamboo nanotubes in all the materials studied in this work.     

Investigation of Fluorine Distribution on the Surface of Acid‐Treated Apatite Single Crystals using Nuclear Resonant Reaction Analysis

The surface of natural fluorine‐containing apatite (fluoroapatite) single crystals treated with acidic solutions of pH between 0.05 and 2.5 was investigated by nuclear resonant reaction analysis (NRRA) techniques using the ¹⁹F(p,αγ)¹⁶O nuclear reaction. The experimental results showed that partial defluoridation takes place due to acid attack characteristically depending on the pH of the solutions. Powder‐XRD data indicated that the crystallinity of the apatite surface was etained despite of the etchpits observed by SEM‐EDS. Relevant investigations of the surface of acid‐treated apophyllite crystals, a typical fluorine‐containing mineral, indicated a complete amorphization and besides a total absence of fluorine.     

Growth and luminescence properties of large‐scale zinc oxide nanotetrapods

Large‐scale zinc oxide (ZnO) nanotetrapods have been grown on p‐type Si (111) substrate by oxidizing zinc pieces in air by thermal evaporation technique without the presence of any catalyst. The size and morphology of the nanostructures was found to depend on experimental parameters. The grown nanostructures were characterized by X‐ray Diffraction (XRD), Photoluminescence (PL), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), High Resolution TEM (HRTEM) and analysis of elemental composition was done by Energy Dispersive X‐ray analysis (EDX). The EDX spectrum shows that the grown product contains Zn and O only. The X‐ray diffraction pattern indicates that the microstructure of the obtained products is typical hexagonal wurtzite ZnO. The optical properties were studied using room temperature PL spectroscopy which indicates that the products are of high optical quality and the near band edge UV transition peak intensity increases with decrease in tetrapod size. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of growth temperature on the structure and optical properties of ZnO nanorod arrays grown on ITO substrate

ZnO nanorod arrays have been successfully prepared on ITO substrate by a chemical‐bath deposition method at different growth temperatures. The influence of the growth temperature on the morphology and microstructure of the ZnO nanorods was investigated by scanning electron microscopy (SEM) and X‐ray diffraction (XRD). The results showed that the diameter of the ZnO nanorods decreased and the size of the nanocrystals increased with increasing growth temperature. Optical absorption measurements showed the absorption band edge has shifted to a lower‐energy region due to the quantum size effect. Green emission and UV emission bands were observed and they are found to be temperature dependent, which indicates that the deep‐level emission and band‐edge emission of ZnO nanorods is closely related to the rod diameter, and the related mechanism is discussed.     

Low temperature synthesis of spindle‐like ZnO nanostructures under microwave irradiation

A simple and general microwave route is developed to synthesize nanostructured ZnO using Zn(acac)₂·H₂O (acac = acetylacetonate) as a single source precursor. The reaction time has a great influence on the morphology of the ZnO nanostructures and an interesting spindle‐like nanostructure is obtained. The microstructure and morphology of the synthesized materials are investigated by X‐ray diffraction (XRD), scanning electron microscopy (SEM), field‐emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). It is found that all of them with hexagonal wurtzite phase are of single crystalline structure in nature. Ultraviolet–visible (UV‐vis) absorption spectra of these ZnO nanostructures are investigated and a possible formation mechanism for the spindle‐like ZnO nanostructures is also proposed.     

Synthesis and growth mechanism of ZnO rod‐like nanostructures by a microwave‐assisted low‐temperature aqueous solution route

A zinc oxide (ZnO) nanoarray (rod‐like nanostructure) was successfully synthesized through a low‐temperature aqueous solution and microwave‐assisted synthesis using zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) and hexamethylenetetramine (HMTA) as raw materials, and using FTO glass as substrate. The effects of parameters in the preparation process, such as solution concentration, reaction temperature and microwave power, on the morphology and microstructure of ZnO nanoarray were studied. Phase structure and morphology of the products were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results indicated that hexagonal wurtzite structure ZnO nanoarray with good crystallization could be prepared through a low‐temperature solution method. When the concentration of the mixed solution was 0.05 M, the reaction temperature was 95 °C, and the reaction time was 4 h, high‐density ZnO regular nanorods of 200 nm diameter were obtained. A possible mechanism with different synthesis methods and the influence of microwave processing are also proposed in this paper.     

耐高温氧化锆-刚玉-莫来石复相陶瓷的制备及其抗热震性

以煤系高岭土、α-Al2O3和部分稳定氧化锆(PSZ, 3;molY2O3)为原料,制备了耐高温氧化锆-刚玉-莫来石复相陶瓷.采用XRD、SEM等测试技术对样品的物相组成及显微结构进行了表征,研究了PSZ添加量(分别为5wt;、10wt;、15wt;、20wt;、25wt;、30wt;)对样品物理性能、高温塑性变形及抗热震性的影响.结果表明:由于采用含3;molY2O3的PSZ,Y2O3在高温下起到了烧结助剂的作用,致使样品的烧成温度显著降低;同时随着PSZ添加量的增加,样品的抗折强度增加.经最佳烧成温度烧成的各样品的抗折强度分别达到147.4 MPa、161.3 MPa、205.9 MPa、234.4 MPa、294.0 MPa、385.0 MPa.当PSZ的最佳添加量为10wt;时,样品具有较低的高温塑性变形及良好的抗热震性;当PSZ添加量继续增加,样品在高温易产生液相,抗蠕变及抗热震性降低.SEM显微结构研究表明,随着氧化锆添加量增加,样品结构越致密,增强效果越显著.XRD分析结果表明,复相陶瓷具有良好的耐高温性能,热震前后样品的物相组成不变,均为莫来石、刚玉、m-ZrO2和t-ZrO2.     

Rapid synthesis of dendrite‐ and platelet‐like α‐Fe2O3 via a hydrothermal oxidation route

Dendrite and platelet‐like α‐Fe₂O₃ microcrystals were synthesized by the oxidation reaction of K₄Fe(CN)₆and NaClO₃ through a simple hydrothermal method. The structures and morphologies of the as‐prepared samples were characterized in detail by X‐ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The experiment results show that NaOH played an important role in controlling the morphology of the final products. The possible mechanism was discussed to elucidate the formation of different morphologies of the α‐Fe₂O₃ microstructures. Besides, the magnetic property of the dendrite α‐Fe₂O₃ microstructure was characterized by a vibrating sample magnetometer (VSM). (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Malic acid assisted precursor route to hierarchical structured nickel oxide

A novel malic acid assisted precursor route to prepare NiO materials with novel hierarchical structures has been investigated in this work. The Ni‐based precursors can be synthesized by a malic acid‐assisted hydrothermal route, which have been characterized by powder X‐ray diffraction (XRD), field‐emission scanning electron microscopy (FE‐SEM), thermogravimetric analysis (TGA). NiO materials can be prepared via the thermal treatment of the precursor in ambient atmosphere. The XRD, SEM, Energy dispersive X‐ray spectroscopy (EDS) and UV‐Vis spectroscopy of the NiO materials were also examined. The effects of the reaction conditions, such as the reaction temperature, the quantity of the raw materials on the morphologies of the precursors were discussed, which indicates that it is an effective method to synthesize NiO materials with different hierarchical structures. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Facile morphology‐controlled hydrothermal synthesis of flower‐like self‐organized ZnO architectures

Flower‐like self‐organized crystalline ZnO architectures were obtained through a facile and controlled hydrothermal process. As‐synthesized products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), electron diffraction and UV‐Vis spectroscopy. XRD and electron diffraction results confirmed the obtained materials are pure wurtzite ZnO. The effects of different ratios of starting materials and solvent on the morphologies of ZnO hydrothermal products were also evaluated by SEM observations. It is suggested that the use of water, rather than ethanol as the solvent, as well as employing a precursor of Zn(Ac)₂ and 2NaOH (v/v) in hydrothermal reactions are responsible for the generation of specific flower‐like self‐assembled ZnO structures. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bi掺杂对Ca3-xBixCo4O9氧化物微观结构和热电性能的影响

采用固态反应法制备Ca3-xBixCo4O9 (0.0≤x≤0.45)样品,并研究了Bi掺杂对样品的微观结构和热电性能的影响.XRD与SEM结果显示,在含Bi样品中形成了c轴取向的结构,x=0.3和x=0.45样品具有大的晶粒取向度和晶粒尺寸,这就导致了这两个样品具有较高的电导率.由于Bi3+替代Ca2+降低了载流子浓度,样品的塞贝克系数随Bi含量的增加而增加.在1000 K,x=0.3样品的功率因子可达2.77×10-4 W/m·K2,这一数值与利用热压法制备的Ca3Co4O9样品的功率因子相当.     

Microstructural Effects of Mn2+ ions in ZnO Nanoparticles

Semiconducting ZnO nanoparticles with manganese content 0 at. %, 5 at. % and 10 at. % were prepared by co‐precipitation technique and XRD reveals that the average crystallite size D is 10.2 nm, 7.62 nm and 7.06 nm respectively. The individual contributions of the size and strain to the XRD peak broadening were investigated by Williamson‐Hall (W‐H) analysis. The strain, stress and energy density were calculated more precisely by uniform deformation model (UDM), uniform stress deformation model (USDM), uniform deformation energy density model (UDEDM) and size‐strain plot (SSP) method. The average particle size from HRTEM analysis is 13 ± 2 nm. The evaluated average crystallite size from the W‐H analysis and SSP method is commensurate with the particle size from HRTEM. Diamagnetic to ferromagnetic phase transition observed is interpreted interms of the anisotropic strain due to the dopant.     

Preparation of monodispersed aragonite microspheres via a carbonation crystallization pathway

Monodispersed calcium carbonate microspheres were prepared by carbonating a calcium acetate aqueous solution with CO₂ gas at a high pressure of 40 bar and a high temperature of 80 °C after 60 minutes of reaction. The products were characterized by X‐ray powder diffraction (XRD) and scanning electron microscopy (SEM), respectively. The XRD pattern showed that the crystal polymorph of the as‐prepared monodispersed microspheres was aragonite. The SEM images also displayed needle‐like aragonite self‐organized into microsphere superstructure with diameters ranging from 5 to 15 μm. Analysis of the formation mechanism of the calcium carbonate microsphere superstructure revealed that the rod‐dumbbell‐sphere morphogenesis mechanism along with the phase transformation of vaterite to aragonite was responsible for the growth of the monodispersed aragonite microspheres. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Co掺杂改性CaTi2O4(OH)2纳米片的溶剂热制备及电化学性能

利用无水氯化钙-钛酸四正丁酯-无水乙醇体系,通过掺杂Co元素,用溶剂热法制备了CaTi2O4(OH)2片状结构.利用X射线衍射(XRD)和扫描电子显微镜(SEM)对样品的显微结构进行检测分析,并利用CHI660E电化学工作站测试掺杂样品电化学性能,研究掺入Co元素对CaTi2O4 (OH)2样品的物相结构、微观形貌以及其电化学性能的影响.实验结果表明:随着钴离子掺入量增加样品的比电容先增加后减小,当Co掺杂量为2;样品的电化学性能最优,且在10 mA/cm2的工作电流密度下,其比电容为496.3 F·g-1.     

WO3薄膜的电致变色与响应时间机理研究

采用直流反应磁控溅射方法制备了纳米WO3薄膜,研究了溅射气压对WO3薄膜的表面形貌和微结构的影响.利用X射线衍射仪和扫描电子显微镜对WO3的微结构进行了表征.采用紫外-可见分光光度计和循环伏安测试系统对样品的电致变色及响应时间性能进行了研究.结果表明,纳米WO3薄膜的微孔结构特征具有较大的比表面积,有利于改善其电致变色性能.当溅射气压为4Pa时,WO3薄膜在可见光区的电致变色平均调色范围达到了71.6;,并且其着色响应时间为5 s,漂白响应时间为16 s.     

Microstructure of Milled Mesophase Pitch-Based Carbon Fibers as an Anode Material for Li-ion Batteries

Abstract

The microstructure of milled mesophase pitch-based carbon fibers (mMPCFs) that have been developed as an anode material for Li ion batteries have been studied as a function of heat treatment temperature (HTT), by SEM, X-ray diffraction, and Raman spectroscopy. And the results obtained are compared with those by X-ray diffraction (XRD) and SEM observations, for the characterization of specific structural features of mMPCFs as a promising anode material.     

Physical properties of Zn‐ 22 wt.% Al‐ x wt.% Ce melt spun eutectoid alloy

Zn‐ 22 wt.% Al (Zn ‐ 40 Al in atomic%) eutectoid alloys with different Cerium (Ce) contents of 0, 1, 2, and 6 (in wt.%), 0.35, 0.70 and 2.1 (in atomic%) were rapidly solidified by melt spun technique. The effects of high cooling rate and alloying element (Ce) on microstructure of the studied alloys were analyzed by X‐ray diffractometry (XRD), scanning electron microscopy (SEM) and electrical resistance measurements. The results showed that the dendrites as well as grains size were refined by the additions of Ce. The main phases in melt spun alloys were α‐Al and η‐Zn, in addition to intermetallic CeZn₅ and Al₄Ce. Additional metastable intermetallic Al_0.71Zn_0.29 phase has been observed only for melt spun alloy of 6 wt.% Ce content. XRD peaks of melt spun alloys demonstrated a considerable broadening with percentage of Ce due to the grain refinement and lattice distortion. Moreover, increase of Ce content results in a decrease of Al lattice constant which could be related to formation of supersaturated solid solution of Zn and/or Ce in α‐Al. Crystallite size of all phases were in the range of nanometer scale which reflects the role of the high cooling rate and the existence of Ce as alloying element for producing nanocrystalline structure. Resistance measurements of melt spun alloys show that the relative resistance rate for the alloys of higher Ce content relaxed faster to lower value than that of lower Ce content. Electrical resistance and microstructure exhibit strongly Ce content dependence.