纳米Fe3 O4 颗粒的正电子湮没谱学研究

测量了磁性纳米Fe₃O₄颗粒的X射线衍射谱(XRD)、正电子湮没寿命谱(PALS)和符合多普勒展宽谱(CDBS),研究了不同压力和退火温度对磁性纳米Fe₃O₄颗粒物相、电子结构、缺陷及电子动量分布等的影响. XRD,PALS,CDBS测量结果表明:纳米Fe₃O₄颗粒的缺陷浓度随压力的增加而增大,但物相和缺陷类型并未发生变化;磁性纳米Fe₃O_{4< 关键词： 正电子 3}O₄')" href="#">Fe₃O₄ 寿命谱 多普勒展宽谱     

Fe3O4-C核壳型纳米纤维的正电子研究

利用正电子手段研究新型多功能材料Fe₃O₄-C 纳米管核壳结构纳米纤维的内部电子结构,通过测量和分析正电子湮没寿命谱和符合双多普勒展宽谱,发现在这种材料中部分正电子在Fe₃O₄内部的单空位中发生湮灭,部分正电子在Fe₃O₄的微空洞中发生湮灭,部分正电子在壳层碳纳米管中湮灭.并估算了各个部分的湮灭比例,在一定程度上揭示了Fe₃O₄-C 关键词： 正电子 纳米纤维 寿命 符合多普勒     

Hg1-xCdxTe晶体缺陷的正电子湮没寿命

利用正电子(e⁺)湮没寿命谱实验研究了Hg_1-xCd_xTe晶体样品的空位缺陷.碲溶剂法生长的样品，不论是n型导电还是p型导电都存在大量的Hg空位.经过合适的退火工艺，p型材料转为n型，同时对正电子的俘获效应减小，表现为正电子湮没平均寿命值减小14—17ps.若退火温度高于350℃，正电子湮没寿命值又增大，表明Hg空位浓度增加.得到HgCdTe中正电子的体寿命为τ_b=272ps.根据正电子湮没寿命和电参数的测量结果，得出 关键词：     

退火处理Fe43Co43Hf7B6Cu1非晶合金的正电子湮没研究

对熔体急冷法制备的Fe₄₃Co₄₃Hf₇B₆Cu₁非晶合金进行了200,300,400和500 ℃保温30 min的退火处理,用正电子湮没寿命谱、X射线衍射、穆斯堡尔谱等方法研究了退火后试样的结构及结构缺陷变化.结果表明,在非晶合金的制备态,正电子主要在非晶基体相空位尺寸的自由体积中湮没,湮没寿命τ₁为158.4 ps,强度I₁关键词： 43Co₄₃Hf₇B₆Cu₁非晶')" href="#">Fe₄₃Co₄₃Hf₇B₆Cu₁非晶 退火处理 正电子湮没寿命 结构与结构缺陷     

温度对ZnO/Al2O3(0001)界面的吸附、扩散及生长初期模式的影响

构建了一个ZnO沉积在α-Al₂O₃(0001)表面生长初期的模型，采用基于密度泛函理论的平面波超软赝势法进行了动力学模拟.发现在400，600和800℃的条件下界面原子有不同的扩散能力，因此温度对ZnO/α-Al₂O₃(0001)表面界面结构以及ZnO薄膜生长初期模式有决定性的影响.在整个ZnO吸附生长过程中，O原子的扩散系数大于Zn原子的扩散系数，O原子的层间扩散对薄膜的均匀生长起着重要作用.进一步从理论计算上证实了ZnO在蓝宝石(0001)上两种生长模式的存在，400℃左右生长模式主要是Zn螺旋扭曲生长，具有Zn六角平面对称特征，且有利于Zn原子位于最外表面.600℃左右呈现为比较规则的层状生长，且有利于O原子位于最外表面.模拟观察到在ZnO薄膜临近Al₂O₃基片表面处，Zn的空位缺陷明显多于O的空位缺陷. 关键词： 扩散 薄膜生长 2O₃(0001)')" href="#">α-Al₂O₃(0001) ZnO     

CoxTi1－xO2－δ体材中氢退火引起的铁磁性及结构相变

利用固相反应法在700℃—1000℃不同的温度下、空气中烧结Co₃O₄ 和TiO₂混合物，制备了(Co₃O₄)_x/3(TiO2)_1-x(03，说明Co₃O₄与TiO₂反应形成了CoT iO₃；同时，在700 ℃低温和900 ℃以上的高温烧结样品中分别观察到了单相的 锐钛矿和金红石相结构.经高低温烧结的样品在500 ℃氢退火后，CoTiO₃相消失 ，锐钛矿相的Co_xTi_1-xO_2-δ形成.X射线光电子能谱(X PS)分析显示，氢退火样品中的Co以+2氧化价态存在，同时没有观察到金属态的Co，这说明 氢退火样品中的室温铁磁性不是源于金属Co颗粒的形成，而是与钙钛矿结构的CoTiO_{3< /sub>相的消失和锐钛矿型的CoxTi1-xO2-δ相的形成 有关.(Co3O4)x/3(TiO2)1-x( 0x}Ti_1-xO_2-δ相的本征铁磁性，伴随着结构相变而产生的Co离子之间的铁磁交换相互作用或 许是样品室温铁磁性产生的根本原因. 关键词： 室温铁磁性 结构相变 锐钛矿 氢退火     

掺镧PbWO4闪烁晶体的缺陷研究

利用正电子湮没寿命谱(PAT)和X射线电子能谱(XPS)研究了掺镧所引起的PbWO₄ 晶体缺陷的变化.结果表明：掺镧后,PbWO₄晶体中的正电子捕获中心铅空位(V< sub>Pb)浓度增加,并进一步诱导低价氧浓度的增加.讨论了掺La的作用机制,认为掺 La将抑制晶体中的氧空位,增加铅空位浓度. 关键词： 掺镧钨酸铅晶体 正电子湮没寿命谱 X射线电子能谱 缺陷     

MoO3/Al2O3催化剂中Mo分散的正电子研究

用浸渍法制备了一系列不同Mo含量的MoO₃/Al₂O₃催化剂.测量了这些样品的正电子湮没寿命谱(PALS)与符合多普勒展宽(CDB)谱,以研究其孔洞结构以及Mo分散.正电子寿命测量结果表明,Al₂O₃载体中存在两种不同尺寸的孔洞.掺入MoO₃之后,Mo原子主要进入Al₂O₃的大孔中,使孔洞体积减小.符合多普勒展宽谱结果表明,当MoO 关键词： 3/Al₂O₃催化剂')" href="#">MoO₃/Al₂O₃催化剂 正电子湮没寿命谱 符合多普勒展宽 Mo 分散     

MOF衍生锌钴复合微结构的制备及环己酮气敏性能研究

采用溶剂热法制备了MOF衍生纯相Zn O和不同比例的Zn O/Co₃O₄复合微结构,通过X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线能量色散谱(EDS)、X射线光电子能谱(XPS)和表面积分析仪对所制备微结构的晶体结构、形貌和化学组成进行了分析.基于上述材料制备气体传感器,探究传感器对多种不同气体的响应特性.实验结果表明:大部分气体传感器在测试温度范围内对环己酮气体的响应值最高,适量Co₃O₄复合可以有效提高Zn O微结构对环己酮的检测性能.Zn O/Co₃O₄复合微结构对环己酮的响应值随Co₃O₄含量的增加先升高后降低,在最佳工作温度(250℃)下锌钴比例1∶0.1的Zn O/Co₃O₄传感器对体积分数为100×10^–6环己酮气体的响应值可达161,是相同条件下ZnO微结构的6.4倍,且响应和恢复时间分别为30 s和35 s,其优异的检...     

外电场下含有缔合缺陷的ZnO/β-Bi2O3界面电学性能

电力设备的安全运行很大程度上取决于避雷器的过电压保护水平, ZnO压敏电阻因具有优异的非线性伏安特性而广泛应用于电力系统避雷器的核心元件.为了从微观结构上了解ZnO压敏电阻的电学性能,本文采用基于密度泛函理论的第一性原理对含有锌填隙Zn_i与氧空位V_o缺陷的ZnO/β-Bi₂O₃界面进行分析计算,并研究其在不同外电场下的相关电学性质.计算结果表明,弛豫后氧空位V_o缺陷发生迁移.在外电场的作用下,填隙Zn离子向界面处偏移,界面能在电场强度超过0.1 V/?后快速升高,界面之间的相互作用力变大,层间距减小,体系导电性迅速增强.采用差分电荷密度、功函数以及Bader电荷分析方法,计算出了界面处的势垒高度,证实了内建电场是ZnO压敏电阻具有非线性伏安特性的重要原因.采用态密度分析的方法,分析了原子轨道能级、陷阱能级以及能隙等微观参数对ZnO压敏电阻宏观导电性能的影响.本工作通过调控外电场的强度对含有缔合缺陷的ZnO/β-Bi₂O₃界面不同电气参...     

Effect of thermal annealing on the structure and magnetism of Fe-doped ZnO nanocrystals synthesized by solid state reaction

High purity Fe₂O₃/ZnO nanocomposites were annealed in air at different temperatures between 100 and 1200 °C to get Fe-doped ZnO nanocrystals. The structure and grain size of the Fe₂O₃/ZnO nanocomposites were investigated by X-ray diffraction 2θ scans. Annealing induces an increase of the grain size from 25 to 195 nm and appearance of franklinite phase of ZnFe₂O₄. Positron annihilation measurements reveal large number of vacancy defects in the interface region of the Fe₂O₃/ZnO nanocomposites, and they are gradually recovered with increasing annealing temperature. After annealing at temperatures higher than 1000 °C, the number of vacancies decreases to the lower detection limit of positrons. Room temperature ferromagnetism can be observed in Fe-doped ZnO nanocrystals using physical properties measurement system. The ferromagnetism remains after annealing up to 1000 °C, suggesting that it is not related with the interfacial defects.     

Magnetoelectric characterization of xNi0.75Co0.25Fe2O4-(1−x)BiFeO3 nanocomposites

Magnetoelectric (ME) nanocomposites containing Ni_0.75Co_0.25Fe₂O₄-BiFeO₃ phases were prepared by citrate sol-gel process. X-ray diffraction (XRD) analysis showed phase formation of xNi_0.75Co_0.25Fe₂O₄-(1−x)BiFeO₃ (x=0.1, 0.2, 0.3 and 0.4) composites on heating at 700 °C. Transmission electron microscopy revealed the formation of powders of nano order size and the crystal size was found to vary from 30 to 85 nm. Dispersion in dielectric constant (ε) and dielectric loss (tan δ) in the low-frequency range have been observed. It is seen that nanocomposites exhibit strong magnetic properties and a large ME effect. On increasing Ni_0.75Co_0.25Fe₂O₄ contents in the nanocomposites, the saturation magnetization (M_S) and coercivity (H_C) increased after annealing at 700 °C. The large ME output in the nanocomposites exhibits strong dependence on magnetic bias and magnetic field frequency. The large value of ME output can be attributed to small grain size of ferrite phase of nanocomposite being prepared by citrate precursor process.     

Effect of annealing on phase composition,structural and magnetic properties of Sm-Co based nanomagnetic material synthesized by sol-gel process

Sm-Co based nanomagnetic material was synthesized by means of a Pechini-type sol-gel process. In this method, a suitable gel-precursor was prepared using respective metal salts and complexing agent such as citric acid. The gel-precursor was dried at 300 °C and then subjected to various reductive annealing temperatures: 350, 500 and 600 °C. The nanopowders so obtained were characterized for their structure, phase composition and magnetic properties. FT-IR studies on the gel-precursor showed the binding of metal cations with the citrate molecules in the form of metal-citrate complex. The gel-precursor, which was annealed at 350 °C showed the presence of both meta-stable cobalt carbide (Co₂C, Co₃C) and Co₃O₄ phases; while the sample annealed at 500 °C indicated the sign of SmCo₅ phase. Upon increasing the reductive annealing temperature to 600 °C, crystalline phase such as fcc-Co and Sm₂C₃ were formed prominently. FE-SEM analysis revealed the change in sample morphology from spherical to oblate spheres upon increasing the annealing temperature. VSM measurements demonstrated ferromagnetic nature at room temperature for all the nanopowders obtained irrespective of their after reductive annealing temperature.     

Birth of room‐temperature magnons and Raman line enhancement in ZnO nanostructures containing cobalt oxide

Cobalt (Co) addition and thermal annealing induced structural and vibrational properties of ZnO nanostructures were analysed. X‐ray diffraction pattern reveals that the nanostructures are in hexagonal wurtzite type and the formation of Co₃O₄. The Co ion induced morphology changes have been studied by high‐resolution scanning electron microscope images and energy dispersive spectroscopy measurements confirm the presence of Co ions. CoO‐related magnon excitation bands are emerged at room temperature for the Co‐added samples. There are no changes in the band positions of the Raman spectra of pure and Co‐added materials. Annealed sample exhibits the suppression of magnon bands and formation of Co₃O₄: ZnO composites. Raman line width and the electron phonon coupling constant are decreased with respect to the annealing temperature. The formation of Co₃O₄ : ZnO composite phases have further confirmed by infrared spectra. Copyright © 2013 John Wiley & Sons, Ltd.     

细菌纤维素模板法制备p-Co3O4/n-ZnO复合材料及气敏特性研究

本文利用细菌纤维素为模板制备了p型Co₃O₄修饰的n型ZnO纳米复合材料，通过XRD、SEM、HRTEM、EDS和XPS等手段对纳米复合材料的组成、形貌与元素分布进行了相应的表征. 相对于纯ZnO来说，p-Co₃O₄/n-ZnO复合材料对有机挥发性气体响应的灵敏度有明显提升，例如复合材料对100 ppm丙酮的灵敏度为63.7(最佳温度为180 °C)，是纯ZnO(最佳温度为240 °C，灵敏度为2.3)的26倍. 从材料表面氧空位(缺陷控制)、Co₃O₄的催化活性以及p-n异质结三个方面解释了复合材料对VOCs的高响应特性. 同时细菌纤维素可以作为模板设计功能化的异质结复合物用于VOCs的测试或者其他应用.     

Effect of high magnetic field annealing on the microstructure and magnetic properties of Co-Fe layered double hydroxide

The effects of high magnetic field (10 T) on the products obtained by calcination of Co-Fe LDH precursors at different temperatures were investigated. The XRD results indicated that Fe^III substituted for Co^III in Co₃O₄ to yield Co^IICo^IIIFe^IIIO₄ under the calcination of Co-Fe LDH precursors at 400 °C. The products obtained by magnetic field annealing at 400 °C had a porous plate-like morphology, whereas the products without magnetic field annealing were composed of nanoparticles. It was seen that CoFe₂O₄ phase could be formed at low temperature (about 500 °C) under the magnetic field annealing. The grain size of products obtained by magnetic field annealing at 800 °C was larger than that of zero magnetic field. It was found that the saturation magnetization was significantly enhanced after magnetic field annealing, especially at lower temperature (≤600 °C). The possible reason for the effects on the microstructure and magnetic properties of products obtained by magnetic field annealing was discussed.     

Laser power influence on Raman spectra of ZnO(Co) nanoparticles

Influence of laser power on nanocrystalline samples of ZnO(Co) prepared by commonly used wet chemistry method followed by calcination was investigated. Previous confirmation of the existence of ZnO and Co₃O₄ phases was based on the X-ray diffraction measurements. Here we report the experimental spectra of non-resonant Raman scattering in the range between 100 cm⁻¹ and 1600 cm^–1, for a series of samples irradiated with four different laser power densities. The laser power density has different influence on relative intensity of peaks that belong to ZnO phase than on those corresponding to Co₃O₄ phase. Both peak types show characteristic broadening and red shift toward lower frequencies. The laser power densities used in our study did not cause thermal destruction in any of the investigated samples. Laser-induced local heating effects in samples caused formation of cobalt dimers on the surface of Co₃O₄.     

NH3气氛处理制备p型ZnO薄膜及性能表征

采用NH₃气氛处理直流/射频共溅射方法制得的ZnO：Al薄膜,从而获得Al+N共掺p型ZnO薄膜.XRD,场发射扫描电子显微镜测试及Hall效应测试发现,处理温度对ZnO薄膜的结构和电学性能具有较大的影响,其中处理温度为700℃时,薄膜具有较好的c轴择优取向,并且薄膜表面平整,结构紧密,晶粒大小均匀,无明显空洞和裂缝,具有良好的表面质量,晶粒尺寸约为40—60nm,薄膜的导电类型由n型转变为p型. 关键词： p型ZnO Al+N共掺杂 直流/射频共溅射     

Exploring the annealing temperature impacting on the magnetic coupling of nanometer soft grain and microstructure hard grain nanocomposites

Nanocomposites of 70% MgFe₂O₄ and 30% BaFe₁₂O₁₉ have been prepared by the mechano-chemical coprecipitation method. The prepared samples were annealed at different temperatures (400, 600, 800, and 1000 °C). The thermal gravimetric analysis (TGA) measurements of the as prepared samples has detected three weight losses attributed to evaporation, the decomposition of citric acid and nitrate combustion and the crystal transformation. The crystal growth of the soft phase has been proved by X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM) measurements. The bonds have been detected by FT-IR measurements and are assigned to the two ferrite phases constituting the nanocomposites, which means that there are no intruder phases that have been detected. The vibrating sample magnetometer measurements (VSM) have displayed a gradually increasing of the saturation magnetization (Ms) with the annealing temperature, while the coercivity (H_c) and remnance (M_r) have exhibited a maximum value at the annealing temperature 600 °C. The ferromagnetic resonance (FMR) and VSM measurements have clarified the magnetic ordering changing inside the nanocomposites at the system transformation from the as prepared amorphous/hexagonal phase to the spinel/hexagonal phase with increasing annealing temperature. The porosity (P), the anisotropy (K) and the line width (ΔH) calculated parameters have been used to study the agreement between the FMR and VSM magnetic measurements.