利用氧化辅助气固法生长高磁性的α-Fe2O3和Fe3O4纳米线

探讨生长α-Fe₂O₃和Fe₃O₄纳米线的一个可控制的合成过程. 在研究中发现,高磁性的α-Fe₂O₃纳米线已经成功地利用氧化辅助气固法结晶生成于Fe_0.5Ni_0.5合金基板上;若基板事先浸泡于草酸溶液中,随草酸浓度的增加,所生长的纳米线晶相会逐转变为Fe₃O₄,当草酸浓度达到0.75 mol/L时,所生长的纳米线几乎全部转变成Fe₃O₄晶相. 此外,实验结果也显示所生长的纳米线长度及直径会随着气固过程中的温度上升而增加,生长密度则会随着气固过程中的流量加大而上升. 此过程所提出的合成程序可在2 h內完成.     

包钴型γ-Fe2O3磁粉矫顽力的研究

包钴型γ-Fe₂O₃磁粉分为包钴γ-Fe₂O₃(简记为Co-γ-Fe₂O₃)和包钴包亚铁γ-Fe₂O₃(简记为CoFe-γ-Fe₂O₃)两种,它们的矫顽力可比γ-Fe₂O₃磁粉的提高100至400Oe左右,本工作对这两种磁粉矫顽力增大的原因作了探讨,认为它们矫顽力增大的机制不同:CO-γ-Fe₂O₃矫顽力增大是由于表面包覆一层Co(OH)₂使表面各向异性增大,而CoFe-γ-Fe₂O₃则是由于表面包覆的是钴铁氧体,γ-Fe₂O₃与钴铁氧体之间发生耦合作用,使矫顽力增大。     

Fe3O4/MgO(100)薄膜的激光分子束外延与磁电学性能

 采用激光分子束外延方法,以烧结α-Fe₂O₃/为靶材,在MgO（100）基底上制备了Fe₃O₄薄膜。通过反射高能电子衍射原位观察了薄膜生长前后的表面结构,结果表明所生长的Fe₃O₄薄膜表面平整。经显微激光拉曼光谱和X光电子能谱分析证实所得薄膜表面成分为纯相Fe₃O₄。磁电学性能采用多功能物性系统测量,结果表明：当温度降至100 K附近时,薄膜电阻率有较大增加,Verwey相转变的范围变宽而且不明显,说明反向晶粒边界的存在;在7 160 kA·m^-1的磁场下,室温磁电阻达到-6.9%,在80和150 K温度下磁电阻分别达到-10.5%和-16.1%;薄膜的室温饱和磁化强度约为260 kA·m^-1,其矫顽磁场约为202 kA·m^-1。     

焙烧温度对SiO2负载的Co3O4纳米粒子表面氧缺陷浓度和CO氧化催化性能的影响

以传统的浸渍法,在不同焙烧温度下制备了用于CO氧化反应的Co₃O₄/SiO₂催化剂．通过激光拉曼光谱(Raman)、X射线光电子能谱(XPS)、X射线衍射(XRD)、程序升温还原(TPR)和X射线吸收精细结构谱(XAFS)表征了该系列催化剂的结构．在所有的催化剂中,XRD和Raman光谱都只检测到了Co₃O₄晶相的存在．与Co₃O₄体相相比,XPS结果表明在200 oC焙烧的(Co₃O₄(200)/SiO₂)催化剂中Co₃O₄表面上存在着过量的Co²⁺．与XPS的结果一致,TPR结果表明Co₃O₄(200)/SiO₂催化剂中Co₃O₄表面上存在氧缺陷, 并且XAFS结果也表明Co₃O₄(200)/SiO₂催化剂中Co₃O₄具有更多的Co²⁺．提高焙烧温度使得过量的Co²⁺进一步氧化为Co³⁺,同时降低了表面氧缺陷浓度,从而得到计量比的Co₃O₄4/SiO₂催化剂．在所有的负载催化剂中Co₃O₄(200)/SiO₂催化剂表现出了最好的CO氧化催化性能,表明过量Co²⁺和表面氧缺陷的存在能够促进Co₃O₄催化CO氧化反应的活性.     

钴改性Fe3O4-MnO2催化转化生物质合成气制备液体燃料

本文制备了用于费托合成反应的钴改性Fe₃O₄-MnO₂双功能催化剂,并探究了钴负载量对Fe-Co协同效应的影响以及Fe₁Co_xMn₁催化剂的费托合成反应性能. 实验发现,在Fe₃O₄-Mn催化剂中加入Co可促进铁氧化物的还原、增加反应过程中铁位点的活性. 此外,Co的加入可增强Fe-Co金属间的电子转移,加强两者的协同作用,提高催化性能. Co负载较高的Fe₁Co_xMn₁催化剂可进一步促进加氢反应能力,使产品分布向短链烃方向转移. 在280 ^°C、2.0 MPa和3000 h^-1的最佳工况条件下,Fe₁Co₁Mn₁催化剂的液体燃料收率最高.     

压力对纳米CoFe2O4/SiO2复合材料结构的影响

 采用溶胶-凝胶工艺和高温高压实验技术,制备了纳米CoFe₂O₄/SiO₂复合材料。利用X射线衍射仪、扫描电子显微镜和振动样品磁强计,对样品的结构、微观形貌和磁性进行了研究,并对CoFe₂O₄中阳离子的占位情况进行了讨论。结果表明,随着处理压力的升高,样品的晶粒尺寸增大,晶格常数减小,比饱和磁化强度增大。通过计算结果可以推断,压力的升高导致CoFe₂O₄中的部分Fe³⁺从A位移向了B位,而部分Co²⁺则从B位移向了A位。     

聚对苯撑/LiNi0.5Fe2O4纳米复合热电材料的制备及其性能研究

本文以流变相反应法原位合成了聚对苯撑/LiNi_0.5Fe₂O₄纳米复合热电材料,并对其热电性能进行表征,研究了放电等离子烧结时保温时间对其热电性能的影响.结果发现,复合材料铁氧体颗粒粒径为100---300nm,其外部被一层聚对苯撑膜包覆.电子在Fe²⁺和Fe³⁺之间的跳跃机理在铁氧体电导中占主导作用,因此聚对苯撑/LiNi_0.5Fe₂O₄复合材料具有n型导电特性.随着保温时间增加,复合材料电导率基本不变,但热导率逐渐增大且Seebeck系数逐渐减小,导致热电优值系数降低.由于结合了有机物高电导率和低热导率以及无机材料高赛贝克系数的优点,所制备的复合材料热电性能较单一材料有较大提高.     

具有介孔结构的MnSiO3@Fe3O4@C纳米粒子的制备以及作为pH响应的T1-T2*双模MRI造影剂的研究应用

本文通过一个简单的、温和的方案制备了平均尺寸为120 nm,介孔结构的纳米粒子MnSiO₃@Fe₃O₄@C. 粒子的细胞毒性微小,可以用作T₁-T₂^*双模MRI造影剂. 酸性条件下MnSiO₃@Fe₃O₄@C释放出大量的Mn²⁺缩短T₁弛豫时间,提高成像分辨率. 超顺磁性的Fe₃O₄可以增强T₂对比成像,检测病变组织. 类似于肿瘤微环境/细胞器的酸性PBS(pH=5.0)中Mn²⁺的释放率达到31.66%,约为中性条件(pH=7.4)下的7倍. 释放的Mn²⁺通过内吞作用被细胞摄取,经肾脏排出,细胞毒性实验表明,MnSiO₃@Fe₃O₄@C具有低的细胞毒性,即使高浓度的200 ppm MnSiO₃@Fe₃O₄@C对HeLa细胞的毒性也相对较小. 对荷瘤小鼠静脉注射定量MnSiO₃@Fe₃O₄@C后,可以观察到一个快速增强的对比成像,给药24 h后,T₁MRI信号显著增强,达到132%,而T₂信号则明显降低至53.8%,活体MR成像证明了MnSiO₃@Fe₃O₄@C可以同时作为阳性和阴性造影剂. 此外,得益于介孔MnSiO₃优秀的酸敏感性,MnSiO₃@Fe₃O₄@C可以作为一种潜在的药物载体,实现肿瘤的诊疗一体化.     

磁场下合成Fe3O4粉体的隧道磁阻

通过在半金属Fe₃O₄合成过程中外加磁场的方法，改变样品粒子的表面结晶状态和晶格缺陷，研究了由此引起的Fe₃O₄输运性质的变化.合成的Fe₃O₄粉体的主要导电机理均为自旋极化隧穿和高阶跃迁电导，电阻随温度升高成指数降低，电阻与电压显示了非线形相关性，磁阻与磁场的关系为蝴蝶形，是典型的隧道磁阻特征.与没有外加磁场时合成的样品比较，外加磁场合成的样品显示了更低的电阻和更高的磁阻.     

Er3+及Er3+/Yb3+掺杂ZrO2-Al2O3的制备及发光性质

采用共沉淀法制备了纳米晶ZrO₂-Al₂O₃∶Er³⁺发光粉体.所制备的粉体室温下具有Er3+离子特征荧光发射,主发射在绿光,其中位于547 nm、560 nm的绿光最强,并得出稀土离子与基质之间有能量传递.对不同煅烧温度下的样品研究表明:因不同温度下所制得的样品晶相不同.研究了纳米晶ZrO2-Al2O3∶Er3+及ZrO₂-Al₂O₃∶Er³⁺/Yb³⁺的上转换发光,并分析了上转换的跃迁机制.发现ZrO₂-Al₂O₃∶Er³⁺的绿光为双光子过程,而ZrO₂-Al₂O₃∶Er³⁺、Yb³⁺的上转换光谱中,红光和绿光也为双光子过程,而极弱的蓝光为三光子过程.讨论了Er³⁺的浓度猝灭现象.最适宜掺杂浓度的原子分数为2%（Er³⁺/Zr⁴⁺）.     

Pulsed reactive crossed beam laser ablation of La0.6Ca0.4CoO3 using O: Where does the oxygen come from?

The composition of thin perovskite films, especially the oxygen content, is a crucial parameter which influences many physical properties, such as conductivity and catalytic activity. Films produced by pulsed laser deposition are normally annealed in an oxygen atmosphere after deposition to achieve a desired oxygen content. In pulsed reactive crossed beam laser ablation, no annealing step is necessary, but a fundamental question regarding this deposition technique is still open: where does the oxygen in the films come from?There are three possibilities, i.e. from the target, from the gas background, or from the gas pulse. To answer this question two experiments were performed: ¹⁸O₂ was used during the deposition process as background gas with ¹⁶O anions in the target and ¹⁶O₂ gas pulse, and a ¹⁸O₂ gas pulse with ¹⁶O from the target and background. These experiments revealed that the quantification of the oxygen origin is only possible, when no oxygen exchange occurs at the deposition temperature. The films are characterized after deposition by elastic recoil detection analysis (ERDA) to determine the ¹⁶O/¹⁸O ratio. Experiments with different oxidizing species in the gas pulse (N₂O and O₂) confirm that the oxidizing potential (N₂O > O₂) as well as the number of molecules are important.     

Role of Ti in the luminescence process of Al2O3:Si,Ti

Al₂O₃:Si,Ti, prepared under oxidizing condition at high temperature, gives PL emission around 430 nm when excited with 240 nm. The Al₂O₃:C, TL/OSL phosphor, also shows emission around 430 nm, which corresponds to characteristic emission of F-center. Thus, to identify the exact nature of luminescent center in Al₂O₃:Si,Ti, fluorescence lifetime measurement studies were carried out along with the PL,TL and OSL studies. The PL and TL in Al₂O₃:Si,Ti show emission around 430 nm and the time-resolved fluorescence studies show lifetime of about 43 μs for the 430 nm emission, which is much smaller than the reported lifetime of ∼35 ms for the 430 nm emission (F-center emission) in Al₂O₃:C phosphor. Therefore, the emission observed in Al₂O₃:Si,Ti phosphor was assigned to Ti⁴⁺ charge transfer transition. Fluorescence studies of Al₂O₃:Si,Ti do not show any traces of F and F⁺ centers. Also, Ti⁴⁺ does not show any change in the charge state after gamma-irradiation. On the basis of the above studies, a mechanism for TSL/OSL process in Al₂O₃:Si,Ti is proposed.     

Oxygen non-stoichiometry and defect thermodynamics in La2Ni0.9Fe0.1O4+δ

The oxygen hyperstoichiometry of K₂NiF₄-type La₂Ni_0.9Fe_0.1O_4+δ, studied by thermogravimetric analysis and coulometric titration in the oxygen partial pressure range 6×10⁻⁵-0.7 atm at 923-1223 K, is considerably higher than that of undoped lanthanum nickelate. The p(O₂)-T-δ diagram of iron-doped lanthanum nickelate can be adequately described by introducing point-defect interaction energy in the concentration-dependent part of defect chemical potentials and accounting for the site-exclusion effects. The critical factors affecting the equilibrium oxygen incorporation process include coulombic repulsion of interstitial anions, trapping of the p-type electronic charge carriers by iron, and interaction between Fe³⁺ and holes localized on nickel cations. Due to low chemical expansion of La₂Ni_0.9Fe_0.1O_4+δ lattice, the thermodynamic functions governing oxygen intercalation, site-blocking factors and hole mobility are all independent of the defect concentrations. The predominant 3+ state of iron cations under oxidizing conditions was confirmed by the Mössbauer spectroscopy. The stability of La₂NiO₄-based phase in reducing atmospheres is essentially unaffected by doping.     

Dielectric and piezoelectric properties of Fe2O3-doped (Na0.5K0.5)0.96Li0.04Nb0.86Ta0.1Sb0.04O3 lead-free ceramics

The effect of a small amount Fe₂O₃ (0.1-2 mol%) doping on the electrical properties of (Na_0.5K_0.5)_0.96Li_0.04Nb_0.86Ta_0.1Sb_0.04O₃ (NKLNTS) ceramics was investigated. It was found that the B-site substitution of Fe³⁺ does not change the crystal structure within the studied doping level and all modified ceramics have a pure tetragonal perovskite structure at room temperature. The addition of Fe₂O₃ can promote the sintering of NKLNTS ceramics, and simultaneously cause the grain growth so that Fe³⁺-doped NKLNTS compositions show degraded densification at higher doping level. Furthermore, the dielectric properties of the NKLNTS ceramics do not show a significant change by Fe₂O₃ doping. However, the addition of Fe₂O₃ was found to have a significant influence on the electric fatigue resistance and the durability against water. The presence of oxygen vacancies caused by the replacement of Fe³⁺ for B-site ions makes the NKLNTS ceramics harder.     

Ion exchange kinetics of polycrystalline Na/Kβ/β″-Al2O3

The ion exchange kinetics of polycrystalline Na/K β/β″-Al₂O₃ soaked in H₂SO₄ were studied. The rate of ion exchange in hot concentrated H₂SO₄ was determined by monitoring the change of solution alkali content. The H₃O⁺ diffusion coefficient was estimated from the resulting time dependence data and the ceramic conductivity calculated. Dilute H₂SO₄ with a constant applied voltage was also studied and the ceramic conductivity calculated from the change of current with time. The estimated conductivities obtained by the two methods are compared with reported values for H₃O⁺-β- and β″-Al₂O₃ single crystals. Utilising an H₃O⁺ jump model, the estimated values reflect intragranular conduction.     

Oxygen nonstoichiometry, Mössbauer spectra and mixed conductivity of Pr0.5Sr0.5FeO3−δ

The oxygen deficiency of perovskite-type Pr_0.5Sr_0.5FeO_3−δ, studied by coulometric titration, thermogravimetry and Mössbauer spectroscopy, is significantly higher than that in La_0.5Sr_0.5FeO_3−δ at 973-1223 K. The variations of hole mobility and Seebeck coefficient in oxidizing atmospheres, where the total conductivity of praseodymium-strontium ferrite is predominantly p-type electronic, suggest progressive delocalization of the p-type charge carriers on increasing oxygen chemical potential. As for other perovskite-type ferrites, reduction leads to the co-existence of vacancy-ordered and disordered domains. The n-type electronic conductivity of Pr_0.5Sr_0.5FeO_3−δ at reduced p(O₂) and the hole transport under oxidizing conditions are both lower compared to the La-containing analogue. Analogous conclusion was drawn for the ionic conductivity, calculated from the steady-state oxygen permeation data under oxidizing conditions and from the p(O₂)-dependencies of total conductivity in the vicinity of electron-hole equilibrium points where the average iron oxidation state is 3+. The similar activation energies for partial ionic and electronic conductivities in Ln_0.5Sr_0.5FeO_3−δ (Ln=La, Pr) indicate that the presence of praseodymium does not alter any of the conduction mechanisms but decreases the charge-carrier mobility due to the smaller radius of Pr³⁺ cations stabilized in the perovskite lattice.     

Improvement of Er:I11/2→Ce:F5/2 energy transfer rate in Er/Ce co-doped TeO2-ZnO-Na2O-Nb2O5 glasses

The B₂O₃ component was introduced into Er³⁺/Ce³⁺ co-doped TeO₂-ZnO-Na₂O-Nb₂O₅ glass to improve energy transfer rate of Er³⁺:⁴I_11/2→Ce³⁺:²F_5/2 phonon-assisted cross-relaxation process. With the 6 mol% substitution of B₂O₃ for TeO₂, the energy transfer rate increased from 1300 to 1831 s⁻¹ and the fluorescence intensity increased by about 13.4%. However, the more B₂O₃ substitution in the same glass system reduced the quantum efficiency of Er³⁺:⁴I_13/2→⁴I_15/2 transition due to the higher OH⁻ group concentration. The results show that an appropriate amount of B₂O₃ component can be used to improve the phonon-assisted energy transfer rate and enhance 1.53 μm fluorescence emission by increasing the phonon energy of host glass. The effect of B₂O₃ on the energy transfer process, the lifetimes of the ⁴I_11/2 and ⁴I_13/2 levels, and the upconversion emission have also been investigated.     

Li2O-(LiCl)2-B2O3-Al2O3系统玻璃的Raman光谱研究

我们用Raman光谱研究了Li₂O(LiCl)₂B₂O₃-Al₂O₃系玻璃的结构,着重研究了Al₂O₃的影响。对于Li₂O-B₂O₃系玻璃,Li₂O含量增加使玻璃中存在的BO₃三角体转变为BO₄四面体, 关键词：     

Y2O3:Yb3+,Tm3+纳米材料的可见及紫外上转换发光

通过燃烧法制备了Yb³⁺-Tm³⁺共掺的Y₂O₃纳米粉体,并对样品在980 nm激光照射下的上转换发光特性进行了研究.实验发现,样品在可见光区域能够产生强烈的蓝色发光(476 nm和487 nm)和较弱的红色发光(约650 nm),而且同时观察到了两个紫外发光峰¹I₆→³H₆ (~297 nm)和^{1关键词： 2O₃:Yb3+')" href="#">Y₂O₃:Yb3+ 3+}')" href="#">Tm³⁺ 上转换光谱 敏化 紫外发光