铁氧化物中电子隧道现象的扫描隧道显微术研究

报道了利用扫描隧道显微术(STM)对金属表面氧化物层进行电子隧道谱研究的结果。在对两类铁晶体表面氧化层进行的隧道谱和势垒高度测量结果进行分析后表明,常温条件下形成的氧化层(Ⅰ类)应主要是Fe₃O₄;而在高温氧化条件下形成的表面层(Ⅱ类)的主要成分则应是Fe₂O₃。从而表明(STM)可用于研究铁表面氧化过程的不同阶段,并且由Ⅰ类氧化层的低势垒特性说明STM还可以用于观测此类氧化层的内部结构。类似研究方法还可应用到对一系列 关键词：     

Bi2O3-Y2O3系高氧离子导体的离子电导和电子电导的研究

用交流电桥法研究了Bi₂O₃-Y₂O₃体系含22.5—30mol％Y₂O₃烧结试样在po₂值由1至10^-21atm范围内氧离子的电导率,实验证明该种材料的氧离子电导率比同温度下ZrO₂基固体电解质高若干倍;用这种材料作为固体电解质组成氧浓差电池,电池电动势和理论电动势的比值E/E₀等于1或接近1,说明这种材料几乎为纯氧离子导体,p型电子空穴导电性很小;用库伦滴定抽氧法测定了含Y₂O₃ 27.5mol％样品的电子导电特征氧分压,其值为lgp_e＇=(-767000/T)+655,电子导电性极小。可期望为一种新型氧离子导体材料。 关键词：     

600℃高温钛合金燃烧组织演变及机理

采用摩擦氧浓度法测定600℃高温钛合金的阻燃性能,通过聚焦离子束技术和高分辨电子显微镜对燃烧组织的燃烧区、熔凝区和热影响区内不同价态的氧化产物进行表征与界面结构分析,发现燃烧产物Al₂O₃,Ti₂O₃以及TiO₂具有不同于氧化过程的形成方式;结合自由能和蒸气压计算,揭示燃烧组织演变的机理及其对合金阻燃性能的影响.结果表明,合金中6%的Al元素含量导致熔凝区/热影响区界面不能形成连续性Al₂O₃保护层;1800 K左右TiO蒸气压的显著增加造成熔凝区形成Ti₂O₃和Ti构成的疏松结构,为氧的快速内扩散提供路径;此外,燃烧区中形成的TiO₂熔体对基体不具有保护作用.因此,600℃高温钛合金不具备良好的阻燃性能.     

Fe2O3上AsH3催化氧化反应机理的理论研究

本文采用密度泛函理论方法研究了Fe₂O₃上AsH₃的催化氧化反应机理.该反应以Fe₂O₃中的两个Fe原子为不同的活性中心进行研究,每个活性中心均设计了3个步骤. AsH₃分子依次与3个O₂分子在催化剂上相互作用分别形成中间体H₃AsO₂、H₃AsO₄及最终产物H₃AsO₆.研究发现,当氧化反应发生在1号铁原子(Fe1)附近,其速度控制步骤活化自由能垒为49.99 kcal/mol;当氧化反应发生在2号铁原子(Fe2)附近,其活化自由能垒为21.20 kcal/mol,与直接氧化(50.14 kcal/mol)相比大大降低.可见AsH₃在Fe₂O₃上的催化氧化反应更易发生在Fe2附近.     

基片温度与氧分压对磁控溅射制备氧化钒薄膜的影响

采用磁控溅射工艺制备了V₂O₅薄膜.通过改变制备工艺中基片温度和氧分压两个条件，研究了薄膜的晶相组成、表观形貌以及氧化物中钒和氧元素的化合价态.当基片温度升高时，V₂O₅薄膜中颗粒结晶由细长针状转变为平行于基片的片状，V⁵⁺状态保持不变，但723 K时氧结合能向高键能态移动.氧分压较低时，薄膜表面有部分V⁴⁺态存在，但存在较多的高键能氧，此时薄膜中晶粒尺寸较小.随着氧分压的提 关键词： 氧化钒 磁控溅射 相变薄膜 X射线光电子能谱     

La掺杂对Bi4Ti3O12薄膜铁电性能的影响

利用Sol-Gel法在Pt/Ti/SiO₂/Si衬底上制备出Bi₄Ti₃O₁₂和Bi_3.25La_0.75Ti₃O₁₂薄膜，研究了La掺杂对Bi₄Ti₃O₁₂薄膜的晶体结构、铁电性能和疲劳特性的影响，发现La掺杂没有改变Bi₄Ti₃O₁₂薄膜的基本晶体结构，并且提高了Bi₄Ti₃O₁₂铁电薄膜的剩余极化值和抗疲劳性能，对La掺杂改善Bi₄Ti₃O₁₂铁电薄膜性能的机理进行了讨论. 关键词： 铁电性能 4Ti₃O₁₂薄膜')" href="#">Bi₄Ti₃O₁₂薄膜 3.25La_0.75Ti₃O₁₂薄膜')" href="#">Bi_3.25La_0.75Ti₃O₁₂薄膜 sol-gel法 La掺杂     

氧流量对热蒸发CVD法生长β-Ga2O3纳米材料的结构及发光特性的影响

用热蒸发CVD法制备了β-Ga₂O₃纳米材料, 并用光致发光(PL)方法研究了其发光特性. Ｘ射线衍射分析显示, 产物为单斜结构的β-Ga₂O₃. 扫描电子显微镜测试表明: 在较小氧流量条件下制备的产物为β-Ga₂O₃纳米带, 宽度小于100nm, 长度有几微米; 较大氧流量时制备出β-Ga₂O₃纳米晶粒结构, 晶粒尺度在80—15 关键词： 光致发光 氧流量 纳米结构 2O₃')" href="#">Ga₂O₃     

Ag/Bi4Ti3O12栅n沟道铁电场效应晶体管制备及存储特性

在溶胶-凝胶工艺获得高质量Bi₄Ti₃O₁₂薄膜的基础上 ，制备了Ag/Bi₄Ti₃O₁₂栅n沟道铁电场效应晶体管. 研 究了Si基Bi₄Ti₃O₁₂薄膜的生长特性及其对铁电薄膜/ 硅的界面状态和铁电场效应晶体管存储特性的影响. 研究表明，在合理的工艺条件下可以获 得具有较高c-轴择优取向的纯钙钛矿相Si基Bi₄Ti₃O₁₂ 铁电薄膜并有利于改善Bi₄Ti₃O₁₂/Si之间的界面特性; 顺时针回滞的C-V特性曲线和C-T曲线表明Ag/Bi₄Ti₃O_{12栅n沟道铁电场效应晶体管具有极化存储效应和一定的极化电荷保持能力; 器件的转移(I< sub>sd}-V_G)特性曲线显示Ag/Bi₄Ti₃O_{12栅n沟道铁电场效应晶体管具有明显的栅极化调制效应. 关键词： 铁电场效应晶体管 4}Ti₃O₁₂')" href="#">Bi₄Ti₃O₁₂ 存储 特性 溶胶-凝胶工艺     

碱性介质电催化体系活性氧的生成及其光谱学研究

亚熔盐液相氧化技术可在相对低温下实现难分解两性金属矿物的高效转化,基于此进一步提出了碱性介质电化学活性氧协同强化新方法。利用紫外-可见光光谱和电子自旋共振波谱等手段对电催化体系活性氧的生成与转化机理进行了系统解析。通过阴极电催化的作用,在电极表面定向进行两电子氧气还原反应,原位产生大量的活性氧组分。研究发现过渡金属离子与两电子氧气还原产物HO-₂之间的“自诱发”效应,可生成具有更高氧化活性的羟基自由基,大幅促进两性金属转化过程,实现了碱性介质电化学高级氧化过程。利用紫外-可见光光谱检测到电化学体系活性氧催化氧化低价两性金属氧化物(Cr₂O₃和V₂O₃)的转化过程。与此同时,根据标准自由能变化的热力学数据计算可知,V₂O₃比Cr₂O₃更易在活性氧存在的条件下发生溶出反应。采用电子自旋共振波谱(ESR)对电催化体系内的羟基自由基进行检测,结果表明由V₂O₃引发的电化学-类Fenton反应激发产生的羟基自由基ESR信号比Cr₂O₃信号强。利用猝灭剂实验验证了具有高氧化电位的羟基自由基可以对两性金属液相氧化起到促进作用。该研究为碱性介质电化学矿物溶出实际反应提供理论参考。     

氮化铌表面氧化物的XPS研究

本文用X射线光电子能谱(XPS)对室温下自然氧化和射频氧化的氮化铌薄膜表面进行了成分分析。指出:与在类似条件下纯铌膜的氧化不同,NbN膜的表面氧化物中不存在NbO和NbO₂,而是以Nb₂O₃作为从NbN到Nb₂O_5-y的过渡相。氮化铌在氧化过程中表现出一种抑制Nb₂O,NbO等低价传导性氧化物生成的能力,这对于用氧化物作势垒的超导隧道结的研制具有实际参考价值。 关键词：     

Initial oxidation stages on FeCr(100) and FeCr(110) surfaces

Simultaneous LEED and AES are used to follow early stages of oxidation of monocrystalline FeCr(100) and (110) between 700 and 900 K in the oxygen pressure range 10^?9–10^?6 Torr. A chromium-rich oxide region at the alloy/oxide interface is observed, which exhibits different surface structures on oxidized FeCr(100) and FeCr(110). The chromium concentration in this initially formed oxide film is found to be enhanced by low oxygen pressures or high temperatures. During further oxidation different behaviours are observed on FeCr(100) and FeCr(110), which are explained by assuming different ion permeabilities through the initial chromium rich oxide regions on the two surface planes. On FeCr(110) surfaces oxidation is initiated on chromium enriched (100) facets at 800 K or below. At 900 K a film consisting of rhombohedral Cr₂O₃ or (Fe, Cr)₂O₃ is epitaxially growing with its (001) plane parallel to the alloy (110) face. On FeCr(100) surfaces the chromium rich oxide region next to the substrate is of fcc type. As soon as the diffusion of iron from the alloy to the gas/oxide interface is observable, a spinel type oxide is formed and connected with the location of iron in tetrahedral lattice sites. Closer to the fcc lattice the spinel oxide consists of FeCr₂O₄ or a solid solution of FeCr₂O₄ and Fe₃O₄ whereas next to the gas phase the oxide is pure Fe₃O₄.     

Oxidation of the (100) surface of a NiFe alloy

The initial stages of oxidation of the (100) surface of a single crystal alloy specimen of approximate atomic composition Ni 59, Fe 41 (at%) have been studied by Auger spectroscopy and electron diffraction techniques. The clean alloy surface shows only a slight iron enrichment over the temperature range of the oxidation studies (373–873 K). Oxidation studies were performed over the O₂ pressure range 5 × 10^?9 to 1 × 10^?6 Torr. Within these experimental conditions the rate of oxygen uptake was found to be linear in pressure and essentially independent of temperature. LEED studies showed that a chemisorbed c(2 × 2) structure preceded the formation of surface oxides. The interaction of oxygen with the surface induced a marked segregation of iron and this was particularly pronounced at elevated temperatures. Chemical shifts were observed in the low energy Ni and Fe Auger spectra during oxidation; these were similar to those previously observed in separate studies of the oxidation of pure Ni and of pure Fe. At the higher temperatures the initial oxide layer grew epitaxially apparently as a (111) cubic oxide on the (100) substrate. The Ni to Fe concentration ratio in oxides several layers thick was found to depend on the temperature of the reaction; at higher temperatures the oxide were more Fe-rich. The Fe to Ni ratio in oxides produced at lower temperatures could be increased by annealing. At large O₂ exposures (about 5000 L) a transition was observed in the structure of the oxide layer.     

The influence of aliovalent impurities on the oxidation kinetics of nickel at high temperatures

The influence of chromium and sodium on the nickel oxidation kinetics has been studied as a function of temperature (1373-1673 K) and oxygen activity (10−10⁵ Pa O₂), using microthermogravimetric techniques. It has been shown that the oxidation of Ni-Cr and Ni-Na alloys, like that of pure nickel, follows strictly the parabolic rate law being thus diffusion controlled. In agreement with the defect model of Ni_1−yO, it has been found that the oxidation rate of the Ni-Cr alloy is higher than that of pure nickel, the reaction rate is pressure independent and the activation energy of this process is lower. This implies that the concentration of double ionized cation vacancies in a Ni_1−yO-Cr₂O₃ solid solution is fixed on a constant level by trivalent chromium ions, substitutionally incorporated into the cation sublattice of this oxide. In the case of the Ni-Na alloy, on the other hand, the oxidation rate is lower than that of pure nickel, the activation energy is higher and the oxidation rate increases more rapidly with oxygen pressure. These results can again be explained in terms of the doping effect, by assuming that univalent sodium ions dissolve substitutionally in the cation sublattice of nickel oxide.     

CEMS study on iron film oxidized in various oxygen pressures

In order to prepare the Fe_1?xO film, Fe metals evaporated on sapphire substrate were oxidized in the furnace for 2 hours at 800°C. The pressure of oxygen between 10^?14 and 10^?19 atm. was controlled by changing the flow rates of CO₂ and H₂ gases. After the oxidation, the conversion Mössbauer spectra for the samples were measured by a He+10%CH₄ proportional counter. It was found that at this temperature the usually accepted Fe_1?xO was not made for 2 hours, but the unknown oxidation state of Fe was formed at the oxygen pressure of 10^?16.5 alm.. Its isomer shift relative to α-Fe and quadrupole splitting are 0.92 mm/sec and 1.71 mm/sec. The normal Fe_1?xO was formed at the oxygen pressure of 10^?16.5 atm. when the oxidation time was extended to 6.5 hours, in addition to Fe₃O₄.     

Defect formation and transport in SrFe1-xAlxO3-δ

Perovskite-related phases derived from SrFeO_3-δ are among known mixed conductors with highest oxygen permeability and are thus of interest as the ceramic membrane materials for oxygen separation and partial oxidation of light hydrocarbons. Dense ceramics of SrFe_1-xAl_xO_3-δ (x=0.1–0.5) were prepared via the glycine-nitrate process. The cubic solid solution formation was found to occur in the concentration range x=0–0.35. Increasing aluminum content leads to decreasing thermal expansion coefficients (TECs), relative fraction of Fe⁴⁺ under oxidizing conditions, and also the total conductivity, predominantly p-type electronic at oxygen pressures close to atmospheric. The TECs vary in the range (13.5–16.4)×10^?6 K^?1 at 373–923 K and increase up to (18.6–31.9)×10^?6 K^?1 at 923–1273 K. The oxygen permeation fluxes decrease moderately with aluminum additions. The Mössbauer spectroscopy data and p(O₂) dependencies of electrical properties indicate a small-polaron mechanism of electronic transport in SrFe_1-xAl_xO_3-δ. Reducing oxygen partial pressure results in transition from dominant p- to n-type electronic conduction. The low-p(O₂) stability limit of SrFe_1-xAl_xO_3-δ perovskites lies between that of LaFeO_3-δ and Fe/Fe_1-γO boundary.     

Partial and complete oxidation of brown coal in a supercritical water–oxygen fluid under conditions of counterflowing reactant streams

The oxidation of brown coal continuously fed as part of a coal–water slurry into a counterflowing stream of a supercritical water–oxygen fluid at a temperature difference along the reactor axis of 673–873 K and a pressure of 30 MPa has been studied. It has been found that, in the case of a partial combustion of coal (under conditions of O₂ deficiency), the yield of hydrogen-enriched products increases owing to heat evolution. Under conditions of excess O₂, coal undergoes complete oxidation. In this case, the heat evolved per unit volume of furnace space is about 1.0 MW/m³. It has been shown that the heat consumed for the implementation of the process using external sources can be partially or completely compensated for by heat evolution during homogeneous and heterogeneous combustion coupled with coal thermolysis.     

Experimental measurement of the electrical conductivity of pyroxenite at high temperature and high pressure under different oxygen fugacities

Electrical conductivities of pyroxenite were measured between frequencies of 10^?1 and 10⁶ Hz in a multi-anvil pressure apparatus using different solid buffers (Ni+NiO, Fe+Fe₃O₄, Fe+FeO and Mo+MoO₂) to stabilize the partial pressure of oxygen. The temperature ranged from 1073 to 1423 K (800 to 1200 °C) and the pressure from 1.0 to 4.0 GPa. We observe that: (1) the electrical conductivity (σ) of pyroxenite depends on frequency; (2) σ tends to increase with rising temperature (T), and Log σ and 1/T obey a linear Arrhenius relationship; (3) under control of the buffer Fe+Fe₃O₄, σ tends to decrease with rising pressure, nevertheless the activation enthalpy tends to increase. For the first time we have obtained values for the activation energy and activation bulk volume of the main charge carriers, which are (1.60±0.07) eV and (0.05±0.03) cm³/mol, respectively; (4) for a given pressure and temperature, σ tends to rise with increased oxygen fugacity, whereas the activation enthalpy and preexponential factor tend to decrease; and (5) the behaviour of the electrical conductivity at high temperature and high pressure can be reasonably interpreted by assuming that small polarons provide the dominant conduction mechanism in the pyroxenite samples.     

PLD of Fe3O4 thin films: Influence of background gas on surface morphology and magnetic properties

Ablation of Fe₃O₄ targets has been performed using a pulsed UV laser (KrF, λ = 248 nm, 30 ns pulse duration) onto Si(100) substrates, in reactive atmospheres of O₂ and/or Ar, with different oxygen partial pressures. The as-deposited films were characterised by atomic force microscopy (AFM), X-ray diffraction (XRD), conversion electron Mössbauer spectroscopy (CEMS) and extraction magnetometry, in order to optimise the deposition conditions in the low temperature range. The results show that a background mixture of oxygen and argon improves the Fe:O ratio in the films as long as the oxygen partial pressure is maintained in the 10⁻² Pa range. Thin films of almost stoichiometric single phase polycrystalline magnetite, Fe_2.99O₄, have been obtained at 483 K and working pressure of 7.8 × 10⁻² Pa, with a high-field magnetization of ∼490 emu/cm³ and Verwey transition temperature of 112 K, close to the values reported in the literature for bulk magnetite.     

Deep reduction behavior of iron oxide and its effect on direct CO oxidation

Reduction of metal oxide oxygen carrier has been attractive for direct CO oxidation and CO₂ separation. To investigate the reduction behaviors of iron oxide prepared by supporting Fe₂O₃ on γ-Al₂O₃ and its effect on CO oxidation, fluidized-bed combustion experiments, thermogravimetric analyzer (TGA) experiments, and density functional theory (DFT) calculations were carried out. Gas yield (γCO₂) increases significantly with the increase of temperature from 693 K to 1203 K, while carbon deposition decreases with the increase of temperature from 743 K to 1203 K, where temperature is a very important factor for CO oxidation by iron oxide. Further, it were quantitatively detected that the interaction between CO and Fe₂O₃, breakage of O-Fe bonds and formation of new C-O bonds, and effect of reduction degree were quantitatively detected. Based on adsorptions under different temperatures and reducing processes from Fe³⁺ into Fe²⁺, Fe⁺ and then into Fe, it was found that Fe²⁺ → Fe⁺ was the reaction-controlling step and the high oxidation state of iron is active for CO oxidation, where efficient partial reduction of Fe₂O₃ into FeO rather than complete reduction into iron may be more energy-saving for CO oxidation.     

The relationship between magnetic behaviour and local structure around Fe ions in Fe-doped TiO2 rutile

The magnetic and structural characterization of Ti_1−xFe_xO₂ (x=0.025, 0.05, 0.07, 0.125, and 0.15) samples prepared by mechano-synthesis using TiO₂ and Fe₂O₃ as starting materials are reported. XANES measurements performed at the Fe K-edge show that Fe ions are in 3+ oxidation state in the 7 at% Fe-doped sample and in a mixture of 2+ and 3+ oxidation states in the other samples. EXAFS results show the incorporation of Fe ions substituting Ti ones in the rutile TiO₂ structure. They also reveal a strong correlation between the number of oxygen nearest neighbours and the Fe²⁺ fraction, i.e the number of oxygen near neighbours decreases when the Fe²⁺ fraction increases. All samples present ferromagnetic-like behaviour at room temperature. We found a clear dependence between saturation magnetization and coercivity with the fraction of Fe²⁺ and/or the number of Fe near neighbour oxygen vacancies.