Preparation and characterization of single crystalline In2O3 films deposited on MgO (110) substrates by MOCVD

Epitaxial indium oxide (In₂O₃) films have been prepared on MgO (110) substrates by metal-organic chemical vapor deposition (MOCVD). The deposition temperature varies from 500 °C to 700 °C. The films deposited at each temperature display a cube-on-cube orientation relation with respect to the substrate. The In₂O₃ film deposited at 600 °C exhibits the best crystalline quality. A clear epitaxial relationship of In₂O₃ (110)|MgO (110) with In₂O₃ [001]|MgO [001] has been observed from the interface area between the film and the substrate. The average transmittance of the prepared films in the visible range is over 95%. The band gap of the obtained In₂O₃ films is about 3.55–3.70 eV.     

Preparation and characterization of heteroepitaxial Zn2SnO4 single crystalline films prepared on MgO (100) substrates

Zinc stannate (Zn₂SnO₄) films were deposited on MgO (100) substrates by pulsed laser deposition, and Zn₂SnO₄ monocrystalline films were obtained by postannealing process. The structures, surface morphologies, and optical properties of the Zn₂SnO₄ films annealed at different temperatures were investigated in detail. Crystal structure analyses showed that the film annealed at 800°C was single crystal Zn₂SnO₄ with an inverse-spinel structure. The heteroepitaxial mechanism was further clarified by a schematic diagram, and the epitaxial relationships between the film and substrate were Zn₂SnO₄ (400) || MgO (200) with Zn₂SnO₄ [001] || MgO [001]. The obtained Zn₂SnO₄ films exhibited excellent transparency. The optical band gap of the 800°C-annealed Zn₂SnO₄ film was about 3.97 eV. The extinction coefficients and refractive indexes of the Zn₂SnO₄ films annealed at different temperatures as a function of wavelength were analyzed in detail.     

MOCVD deposition of CoAl2O4 films

Cobalt aluminate (CoAl₂O₄) thin films were grown in a low-pressure hot wall metal organic chemical vapour deposition (MOCVD) reactor on Si(1 0 0) and quartz substrates with a total pressure of 2 Torr using bis(η⁵-cyclopentadienyl)Co(II) [Co(η⁵-C₅H₅)₂] and aluminium dimethylisopropoxide [AlMe₂(OⁱPr)] as precursors at 500 and 900 °C. Films showed a dark-brown and dark-green colouration, respectively, and after an overnight heat treatment in air at 1200 °C, they turned blue. Film microstructure, composition and morphology were investigated in detail by X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), scanning electron microscopy (SEM) and secondary ion mass spectrometry (SIMS) analyses. Films were polycrystalline and the UV-vis spectra showed three electronic transitions allowed by the spin (540-630 nm range) characteristic of Co(II) ions with 3d⁷ configuration in tetrahedral coordination. SEM micrographs of the heat-treated CoAl₂O₄ samples revealed the presence of agglomerated crystallites with a highly porous structure.     

Characterization of MgAl2O4 Precursor Powders Prepared by Aqueous Route

MgAl₂O₄ spinel precursors have been prepared by two different aqueous synthesis routes: spray drying and citrate complexing. The spinel precursors exhibit different morphology and crystallization behavior. ²⁷Al high-resolution magic-angle spinning (MAS), multiple quantum MAS, and ²⁷Al-{¹H} rational echo double resonance (REDOR) nuclear magnetic resonance experiments, show that the spinel precursors have different aluminum local structures. ²⁷Al-{¹H} REDOR experiments detect Al_IV- and Al_V-bearing proton-free domains, possibly stabilized by residual carbonates, characteristic of the complexed precursor.     

透明MgAl2O4晶须的制备与表征

本文采用MgO粉和金属Al粉为原料,在氮气气氛下制备MgAl2O4晶须,研究了TiO2、SiO2或Cr2O3等供氧添加剂和制备条件对晶须合成率的影响并分析了晶须的物相组成和结构.结果表明:最佳MgO/Al=2/3;添加SiO2或Cr2O3不利于晶须合成;添加TiO2对合成晶须有促进作用,最佳TiO2加入量为40%;采用氧化铝坩埚比采用釉面陶瓷坩埚好,最佳保温时间为6 h.合成的晶须为MgAl2O4,空间群Fd3M,晶格常数a=b=c=0.8083 nm,MgO 28.3%,Al2O3 71.7%;晶须呈透明柱状,最大长度为20～30 mm,长径比20～400.     

共沉淀-真空冷冻干燥法制备纳米MgAl2O4粉体

以硝酸镁和硝酸铝为主要原料,NH3·H2O为沉淀剂,用均相混合物共沉淀法制得镁铝混合均匀的溶胶,再用真空冷冻干燥(VFD)方法在-50℃,13.3 Pa的真空度下制得MgAl2O4的前驱体粉体.用TG-DSC、XRD、TEM及Autosorb-1-M等仪器研究了热处理温度及反应体系的pH值对镁铝均匀混合纳米粉体材料的物相转变、显微形貌、表面性能等的影响.研究表明控制溶液的pH值在9.0附近,采用共沉淀-真空冷冻干燥方法,可制得粒径小、比表面积大的MgO-Al2O3二元混合纳米粉体,且其起始尖晶石化温度在600℃,经过1000℃2 h处理后,已全部转变成粒径为50 nm左右的纳米尖晶石,比传统制备镁铝尖晶石的温度低500～600℃.     

Interfacial evolution mechanism of MgAl2O4/MgAl2O4 joints bonded with lanthanum glass

The La₂O₃-SiO₂-B₂O₃ (LSB) glass filler with high softening temperature was first used to join MgAl₂O₄ ceramic. An interfacial layer composed of Al₂O₃ was formed due to the solubility difference of MgO and Al₂O₃ in the LSB glass filler. As a result, the addition of Al₂O₃ into the LSB glass filler caused the increase of interfacial layer thickness. On the contrary, the addition of MgO into the LSB glass filler led to the decrease of interfacial layer thickness. When the adding content of MgO was 6 wt%, the interfacial layer disappeared and completely amorphous brazing seam was obtained. The in-line transmittance of joints decreased with the increase of the thickness of interfacial layer. The optimal in-line transmittance of joint bonded with La₂O₃-SiO₂-B₂O₃-MgO (LSB6M) glass filler reached 82.9% at 1000 nm. Meanwhile, the average flexural strength of joints was about 196.2 MPa, which was equal to the strength of MgAl₂O₄ substrate.     

TiO2纳米粉末的热壁低压MOCVD方法制备

采用热壁低压ＭＯＣＶＤ方法制备了ＴｉＯ２纳米粉末。研究了收集区、载气流量和氧化气流量对ＴｉＯ２纳米粉末的晶体结构、平均晶粒尺寸和粒度分布的影响规律。采用Ｒａｍａｎ散射、Ｘ射线衍射和航向电子显微镜等技术对ＴｉＯ２纳米粉末进行了表征。     

微波辅助溶液燃烧法制备MgAl_2O_4粉体

将硝酸镁、硝酸铝、尿素按物质的量比为1 2 6.66制得透明混合前驱液,用低温燃烧技术与微波加热技术相结合的方法制备了高纯度、低团聚的镁铝尖晶石(MgAl2O4)粉体。研究了燃烧反应过程中,微波输出功率(200、400、600、700 W)对Mg Al2O4粉体晶体结构、形貌及比表面积的影响。结果表明:微波高效加热方式导致燃烧反应瞬间产生大量气体,促进了Mg Al2O4超细颗粒的形成。同时,随着微波输出功率的增加,尿素氧化加速,利于MgAl2O4晶粒的生长发育。在微波功率700W,微波时间2 min的条件下,可制备结晶完整,粒度分布均匀(平均晶粒尺寸为56.03 nm)的Mg Al2O4粉体。     

Barium titanate thin films prepared on MgO (100) substrates by coating-pyrolysis process

Barium titanate (BaTiO₃) thin films were prepared on MgO (100) substrates using metal naphthenate solution by a coating-pyrolysis process. Amorphous films pyrolyzed at 470‡C were crystallized to BaTiO₃ phase by heat treatment at higher temperatures. The crystallinity and alignment of the films depended on temperature and on atmosphere during heat treatment. Epitaxial BaTiO₃ film having (100)-orientation was obtained by heat treatment at 900‡C under oxygen partial pressure of 2x 10^-4 atm. The epitaxial BaTiO₃ film had a lattice constant of 0.401₆ nm and displayed a smooth surface with some pores dispersed on the surface. By heat treatment in air, amorphous BaTiO₃ film was obtained at 900‡C or below, and textured film with less strong (100) orientation was obtained at 1,200‡C and consisted of grains with diameter about 0.3 Μ.     

Nano-structured MgAl2O4 spinel consolidated by high pressure spark plasma sintering (HPSPS)

Nano-structured transparent polycrystalline magnesium aluminate spinel (PMAS) was fabricated using a high pressure (up to 1000 MPa) spark plasma sintering (HPSPS) apparatus and various properties of the spinel, such as transparency, micro-structure and mechanical properties (specifically, hardness and fracture toughness), were tested. Using a creep densification model, it was concluded that densification in the final stage of HPSPS is controlled by grain boundary sliding (GBS), rather than by oxygen diffusion. The average grain size of PMAS fabricated under 400 MPa pressure at 1200 °C was about 170 nm, while for samples fabricated under 1000 MPa at 1000 °C the average grain size was remarkably smaller (about 50 nm). HRTEM analysis clearly demonstrated clean grain boundaries and triple points with no evidence for the existence of amorphous regions. Fully dense specimens displayed in-line transmittance higher than 80%. It was moreover established that hardness and fracture toughness values did not depend on the indentation load applied. Finally, hardness values for grains sized between tens of microns and tens of nm strictly followed the Hall-Petch relationship.     

在尖晶石结合浇注料中尖晶石的结构分析

普通的水合镁盐和廉价的一水软铝石溶胶的混合物被认为是有经济效益的活性纳米尖晶石（1∶1）粉末的前身。它经机械化学处理后,在控制pH值、温度和时间的条件下凝胶,并在低温下煅烧。利用X-射线衍射（XRD）、红外光谱、差热分析、质子核磁共振（NMR）和透射电子显微镜来研究水合尖晶石中低纳米晶体域的初期形成。骨料表面上（OH）基的薄吸附层保护了尖晶石纳米粒子。对传统Al2O3尖晶石和Al2O3-MgO浇注料的选择属性和将尖晶石细粉用化学途径以相同的配方制出的浇注料进行比较。在有商用尖晶石的耐火浇注料中添加过量铝粉的情况下,其冷热强度最好,而通过活性氧化镁和沉淀的尖晶石细粉结合的工业尖晶石不是非常令人满意。溶胶-凝胶尖晶石的性能与含有78%氧化铝的预制尖晶石具有可比性。     

用MOCVD方法制备TIO2薄膜：工艺及进展

本文概述了用金属有机物化学气相沉积（ＭＯＣＶＤ）的方法制备了ＴＩＯ２薄膜的原理工艺过程用工艺特点，并指出了最新研研进展和存在的问题以今后及发展方向。     

溶胶-凝胶法制备纳米镁铝尖晶石纳米粉

以硝酸镁和硝酸铝为原料,柠檬酸为络合剂,混合后制得柠檬酸盐先驱体,并将脲加到柠檬酸盐先驱体中,得到另一种新的含脲柠檬酸盐先驱体.两种先驱体分别经800 ℃和1000 ℃煅烧,可得到镁铝尖晶石纳米粉.XRD分析表明,800 ℃煅烧已有镁铝尖晶石形成,镁铝尖晶石结晶化程度随煅烧温度的升高而提高,而在同一热处理温度下,含脲柠檬酸盐前驱体比柠檬酸盐前驱体制得的纳米镁铝尖晶石颗粒细.TEM结果表明:800 ℃煅烧含脲柠檬酸盐可得到的镁铝尖晶石纳米粉体,颗粒大小均匀,粒径尺寸在20～30 nm.     

Photocatalytic activity of undoped and sulfur-doped TiO2 films grown by MOCVD for water treatment under visible light

Titanium dioxide ceramic coatings have been used as catalysts in green technologies for water treatment. However, without the presence of a dopant, its photocatalytic activity is limited to the ultraviolet radiation region. The photocatalytic activity and the structural characteristics of undoped and sulfur-doped TiO₂ films grown at 400 °C by metallorganic chemical vapor deposition (MOCVD) were studied. The photocatalytic behavior of the films was evaluated by methyl orange dye degradation under visible light. The results suggested the substitution of Ti⁴⁺ cations by S⁶⁺ ions into TiO₂ structure of the doped samples. SO₄^2? groups were observed on the surface. S-TiO₂ film exhibited good photocatalytic activity under visible light irradiation, and the luminous intensity strongly influences the photocatalytic behavior of the S-TiO₂ films. The results supported the idea that the sulfur-doped TiO₂ films grown by MOCVD may be promising catalysts for water treatment under sunlight or visible light bulbs.     

Synthesis of MgAl2O4 Whiskers by an Oxidation-Reduction Reaction

Magnesium aluminate whiskers were synthesized by an oxidation—reduction reaction between MgO, C, and Al in a CO and CO₂ atmosphere. The oxygen partial pressure suitable for MgAl₂O₄ whisker growth ranged from 10^−12.1 to 10^−11.5 MPa. The average whisker diameter and length formed at 1500°C for 8 h were ∼3.1 μm and ∼4 mm, respectively. The whiskers grew in the [111] direction.     

非水解sol-gel法合成MgAl2O4纳米粉体

以无水三氯化铝和无水氯化镁为主要原料,采用非水解sol-gel法合成了镁铝尖晶石纳米粉体,研究了氧供体种类(分别为无水乙醇、无水异丙醇和无水异丙醚)、加料顺序及凝胶化温度(分别为90、110、130℃)对镁铝尖晶石合成的影响.结果表明:1)以乙醇为氧供体合成镁铝尖晶石的产率高于以异丙醇和异丙醚为氧供体合成镁铝尖晶石的产率;2)先将无水氯化镁加入到氧供体与二氯甲烷的混合溶液中,再加入无水氯化铝的加料顺序有利于镁铝尖晶石的合成;3)凝胶化温度为110℃有利于镁铝尖晶石的合成,干凝胶经900℃煅烧可合成出平均粒径为50 nm左右的高纯镁铝尖晶石纳米粉体.     

Electrochemical Impedance Spectroscopy of Transparent Polycrystalline Magnesium Aluminate (MgAl2O4) Spinel

Transparent polycrystalline magnesium aluminate spinel is one of few materials capable of fulfilling certain demanding optical applications. However, LiF additive typically required to enhance sintering and impart transparency also degrades mechanical properties and causes scatter, precluding wider application. To shed light on the cause of altered properties, electrochemical impedance spectroscopy was performed between 500°C and 900°C, in oxidizing and reducing atmosphere, on fully dense, polycrystalline spinel compacts hot‐pressed with and without LiF. In combination with electron microscopy, chemical analysis, and secondary‐ion mass spectroscopy, bulk and grain‐boundary dielectric behavior were related to microstructure and chemistry. Decades higher conductivity than for comparable single crystals correlated with Al₂O₃‐rich stoichiometry, impurities, and small grain size, and suggested increased conduction and current‐line detouring along Mg‐depleted, impurity‐rich, field‐parallel grain boundaries. LiF addition reduced conductivity by one decade and increased the activation energy for conductivity, attributed to impurity removal, larger grain size, and point defects caused by lithium incorporation.     

Micromechanics of impact damage of ductile (ZnS) and hard (MgAl2O4) ceramics

The time-resolved generation of the electromagnetic emission (EME) and acoustic emission (AE) excited by the point impact loading of ductile ZnS and hard MgAl₂O₄ ceramics was detected. It has been found that the EME generation precedes the AE activity in loaded ZnS ceramics, while the EME signal lags the AE generation from MgAl₂O₄. This dissimilarity of temporal patterns was explained by the difference between the mechanisms of the excitation of electrical charges in loaded ductile and hard ceramics. The EME from loaded ZnS is caused by the motion of charged dislocations, while, the EME effect in MgAl₂O₄ is due to the annihilation of opposite electric charges emerged on microcrack edges. The AE energy yield from growing microcracks in both ceramics as well as the EME activity in MgAl₂O₄ were found to be random (Poissonian-like), which is typical of the localized fracture of solids occurring without long-range interactions between perturbed structural localities. The energy distribution in EME time series generated in ductile ZnS prior to cracking followed a power law, which is characteristic for the correlated motion of charged dislocations at the stage of plastic flow. The temporal patterns of damage accumulation at different structural levels were specified through physical and mechanical properties of tested materials.     

用MOCVD法制备铁系云母珠光颜料

以Fe(CO) 5为物源 ,在常压喷动流化反应器中 ,以金属有机化学气相沉积 (MOCVD)法对云母粉进行包覆 ,制备铁系 -云母珠光颜料。实验结果表明 :在沉积温度 2 5 0℃ ,氧气流量 3mL·s-1,沉积时间 5min时能得到棕色色泽的珠光颜料 ;随着沉积温度的提高和反应时间的延长 ,可获得红棕、金红、橙红、深红等不同色泽的珠光颜料。用色差仪测定颜料的明度值L 、红度值a 、黄度值b ;X衍射仪表征颜料的表面成分 ;酸滴定计算氧化物的涂覆率。探讨了温度、时间、氧量对珠光颜料表面成分和珠光光泽的影响