放电等离子烧结原位合成LaxCe1-xB6化合物及性能研究

以LaH₂, CeH₂纳米粉和无定形B粉为原料, 通过放电等离子烧结原位合成法制备了单相、高致密度的La_xCe_1-xB₆稀土六硼化物. 系统研究了该系列化合物的晶体结构、表面织构、力学性能、电输运特性及热发射性能. 结果表明, 该方法制备出的样品致密度均高于96%, 维氏硬度最高值达到2310 kg/mm², 说明具有良好的力学性能. 热发射结果表明, 当阴极温度为1873 K, 外加电压为1 kV时, La_0.6Ce_0.4B₆的最大发射电流密度达到40.7 A/cm², 该值高于单纯LaB₆和CeB₆电流密度值. 因此, La_xCe_1-xB₆多元稀土六硼化物作为热阴极材料将有良好的应用前景. 关键词： 稀土六硼化物 阴极材料 热电子发射     

多元纳米稀土六硼化物Nd1-xEuxB6粉末的制备及光吸收研究

在真空环境中采用固相烧结法成功制备出了多元稀土六硼化物Nd1-xEuxB6纳米粉末.系统研究了Eu掺杂对纳米NdB6物相、形貌及光吸收性能的影响规律.结果表明,所有合成的纳米粉末物相均为单相的CsCl型晶体结构,具有立方形貌,平均晶粒尺度为30 nm.光吸收实验结果表明,随着Eu掺杂量的增加,纳米NdB6透射光波长从629 nm红移至1000 nm以上,表现出了透射光波长的可调特性.此外,NdB6和EuB6同步辐射吸收图谱表明,Nd和Eu原子分别以Nd^3+和Eu^2+形式存在于纳米NdB6和EuB6中,充分说明了Eu掺杂使NdB6传导电子数量减少,从而导致其等离子共振频率能量的降低.采用第一性原理计算了NdB6和EuB6的能带结构、态密度、介电函数以及等离子共振频率能量,从而定性解释了Eu掺杂使NdB6透射光波长红移的特性.     

富硼稀土硼化物NdB6的高温高压合成

 提出了一种在高温高压极端条件下合成富硼稀土硼化物NdB₆的新方法，即以稀土氧化物Nd₂O₃为钕源与单质硼反应的方法获得了稀土六硼化物NdB₆。并对合成产物进行了粉末X射线衍射分析。结果表明在配比为Nd：B＝1：6时，压力为4.0 GPa、温度为1 600 ℃、反应时间为15 min的条件下，获得了单相性非常好的NdB₆。高温高压合成NdB₆方法具有反应条件易达到、合成时间短、反应产物单相性好等优点。其XRD结果表明该合成产物为立方结构，晶格常数为a＝0.417 nm。     

(Fe1-xCox)3BO5纳米棒磁性的研究

本文采用高温有机溶剂法制备了(Fe_1-xCo_x)₃BO₅纳米棒, 通过控制反应物中乙酰丙酮钴的含量合成了不同Co含量的(Fe_1-xCo_x)₃BO₅. 利用高分辨透射电子显微镜(HRTEM)、超导量子干涉磁强计(SQUID)对其形貌和磁性能进行了表征. 高分辨透射电子显微镜结果表明制备出的纳米(Fe_1-xCo_x)₃BO₅为多晶棒状, 且具有多折孪晶结构; 磁性测量的结果表明,(Fe_1-xCo_x)₃BO₅纳米棒在室温下表现出铁磁性, 随着Co含量的增加, 纳米棒的铁磁性逐渐增加, 该纳米棒有望用来研究生物大分子的机械性能.     

Ba1-xSrxTiO3及Ba0.6-xPbxSr0.4TiO3陶瓷的制备和介温特性研究

用固相反应法制备了Ba_1-xSr_xTiO₃(BST)及Ba_0.6-xPb_xSr_0.4TiO₃(BPST)陶瓷,通过XRD,FESEM和拉曼谱分析了Pb掺杂对Ba_0.6Sr_0.4TiO₃样品的晶格、相变及表面形貌的影响.测试了BST及B 关键词： BST BPST 弥散相 介温特性     

Pr1-xCexB6阴极材料的原位反应合成及性能研究

本文以CeH2,PrH2纳米粉和B粉为原料,在无氧环境下采用放电等离子原位反应成功制备了单相多元稀土六硼化物Pr1-xCexB6=（x=0．2—0．8）阴极材料．系统研究了掺杂元素Ce对Pr1-xCexB6的物相组成、力学性能及热电子发射性能的影响．结果表明,当烧结温度为1450℃,烧结压强为50MPa时可制得单相的Pr1-xCexB6多晶块体材料并且该系列样品具有良好的力学性能,维氏硬度和抗弯强度最高值分别达到了24．34GPa和226．02MPa,已达到单晶水平．热电子发射性能结果表明,随着Ce掺杂量的增加Pr1-xCexB6的发射电流密度线性增加．当阴极温度为1973K,外加电压为950V时,Pr0．4Ce0．686最大发射电流密度达到47-3A．cm^-2,该值远高于传统热压烧结法制备的发射电流密度．因此,本文该方法制备的Pr1-xCexB6多晶块体具有良好的力学性能和发射性能,作为热阴极材料将会有很好的应用前景．     

超细SnO2纳米晶粒带边光吸收的线度效应

采用超细过滤方法,分别制备含有平均线度小于2nm的超细SnO₂纳米晶粒的酸性和碱性溶胶溶液.通过动态光散射、X射线衍射和晶粒透射电子显微镜像测量,确定了SnO₂晶粒的线度.对其光吸收谱测量发现,超细过滤后酸性和碱性溶胶溶液中晶粒的带边光吸收能量均有明显蓝移.分析结果表明,SnO₂晶粒的线度减小是同类晶粒带边光吸收蓝移的主要原因. 关键词： 超细纳米晶粒 透射电子显微镜 带边光吸收 表面化学修饰     

MnxSi1-x磁性薄膜的结构研究

利用X射线衍射(XRD)和X射线吸收近边结构(XANES)方法研究了在Si(100)衬底上及600℃温度条件下用分子束外延(MBE)共蒸发方法生长的Mn_xSi_1-x磁性薄膜的结构.由XRD结果表明,只有在高Mn含量(8％和17％)样品中存在着Mn₄Si₇化合物物相.而XANES结果则显示,对于Mn浓度在0.7%到17%之间的Mn_xSi_1-x样品,其Mn原子的XANES谱表现出了一致的谱线特征.基于多重散射的XANES理论计算进一步表明,只有根据Mn₄Si₇模型计算出的理论XANES谱才能够很好的重构出Mn_xSi_1-x样品的实验XANES谱.这些研究结果说明在Mn_xSi_1-x样品中,Mn原子主要是以镶嵌式的Mn₄Si₇化合物纳米晶颗粒存在于Si薄膜介质中,几乎不存在间隙位和替代位的Mn原子. 关键词： xSi_1-x磁性薄膜')" href="#">Mn_xSi_1-x磁性薄膜 分子束外延 XRD XANES     

锂离子电池LiMn1-xFexPO4(0<x<1)正极材料的制备及性能研究

本文采用固相法制备了纯相LiMn_1-xFe_xPO₄/C (x=0.2,0.4,0.6)正极材料,并用X射线衍射(XRD)和扫描电镜(SEM)进行表征,用高精度电池测试系统进行充放电和循环伏安测试.结果表明不同Mn和Fe原子比的电极材料具有很大的性能差异,其中当x=0.4时,材料具有优异的循环稳定性和较高的可逆容量.首次充电容量和放电容量分别达到141.5 mAh/g和125.7 mAh 关键词： 锂离子电池 固相法 1-xFe_xPO₄')" href="#">LiMn_1-xFe_xPO₄ 正极材料     

Bi1-xLaxFeO3±δ薄膜的快速制备及铁电性

样品的制备是对影响样品质量的各个工艺参数进行优化的过程. 传统的试错法是对各个参数逐个进行尝试, 需要的周期较长. 与传统的单参数尝试法相比, 高通量样品制备方法可以对参数实现并行筛选, 因而极大地缩短了优化工艺所需的时间. 本工作借助高通量制备方法成功实现系列镧掺杂BiFeO₃薄膜的快速优化, 包括对烧结温度、镧元素含量和高温固态反应气氛等关键工艺参数的快速筛选, 同时分析了不同生长条件下样品的结构并测试了其铁电性. 实验结果表明: 1) 560 ℃ 烧结可得到单相薄膜; 2)测量不同La含量样品的铁电性, 发现当E=75 kV/cm时, La=15%的样品剩余极化值(2Pr)最大, 约为26.7 μC/cm²; 3) 在纯氧气氛下烧结有助于得到结晶性更好的单相Bi_0.75La_0.25FeO_3±δ 薄膜, 并且能够提高薄膜的铁电性.     

Synthesis, thermionic emission and magnetic properties of (NdxGd1-x)B6

Polycrystalline rare-earth hexaborides(NdxGd1-x)B6(x = 0,0.2,0.6,0.8,1) were prepared by the reactive spark plasma sintering(SPS) method using mixed powder of GdH2,NdH2 and B.The effects of Nd doping on the crystal structure,the grain orientation,the thermionic emission and the magnetic properties of the hexaboride were investigated by X-ray diffraction,electron backscattered diffraction and magnetic measurements.It is found that all the samples sintered by the SPS method exhibit high densities(> 95%) and high values of Vickers hardness(2319 kg/mm2).The values are much higher than those obtained in the traditional method.With the increase of Nd content,the thermionic emission current density increases from 11 to 16.30 A/cm2 and the magnetic phase transition temperature increases from 5.85 to 7.95 K.Thus,the SPS technique is a suitable method to synthesize the dense rare-earth hexaborides with excellent properties.     

锆钛酸铅双层膜的铁电及光学特性研究

采用化学溶液沉积法在LaNiO₃涂布的硅晶片上制备了高度(100)择优取向,表面均匀、平整、致密无裂纹的PbZr_0.5Ti_0.5O₃/PbZr_0.4Ti_0.6O₃双层膜. 双层膜具有单一的钙钛矿相,同时拥有良好的铁电性能,剩余极化强度高达64μC/cm²,平均矫顽场仅为43.6kV/cm. 棱镜-薄膜耦合实验结果表明PbZr_{关键词： 铁电薄膜 平板光波导 锆钛酸铅 棱镜-薄膜耦合}     

The optical properties of MgxZnl-xO thin films

Mg_xZn_1-xO thin films have been prepared on silicon substrates by radio frequency magnetron sputtering at 60℃. The thin films have hexagonal wurtzite single-phase structure and a preferred orientation with the c-axis perpendicular to the substrates. The refractive indices of Mg_xZn_1-xO films are studied at room temperature by spectroscopic ellipsometry over the wavelength range of 400--760\,nm at the incident angle of 70℃. Both absorption coefficients and optical band gaps of Mg_xZn_1-xO films are determined by the transmittance spectra. While Mg content is increasing, the absorption edges of Mg_xZn_1-xO films shift to higher energies and band gaps linearly increase from 3.24.eV at x=0 to 3.90\,eV at x=0.30. These results provide important information for the design and modelling of ZnO/ Mg_xZn_1-xO heterostructure optoelectronic devices.     

Density-functional theory investigation of energy gaps and optical properties of Hg1-xCdxTe and In1-xGaxAs

We use a modified Becke-Johnson exchange plus a local density approximation correlation potential within the density functional theory to investigate the electronic structures of Hg_1-xCd_xTe and In_1-xGa_xAs with x being 0, 0.25, 0.5, 0.75, and 1. For both of the two series, our calculated energy gaps and dielectric functions (real part ε₁ and imaginary part ε₂) are in agreement with the corresponding experimental results with x being between 0 and 1. The calculated zero-frequency refractive index varies greatly with x for Hg_1-xCd_xTe, but changes little with x for In_1-xGa_xAs, which is consistent with the real parts of their dielectric functions. Therefore, this new approach is satisfactory to describe the electronic structures and the optical properties of the semiconductors.     

(Fe1-xNix)2P电子结构与磁学特性的X射线近边吸收谱研究

利用X射线近边吸收谱对Fe₂P,Ni₂P及其掺杂物(Fe_1-xNi_x)₂P(x=01,025,05)中Fe,Ni,P的K边进行了研究.结合多重散射理论近边计算,讨论了金属原子不同位置格点3f,3g对近边谱特征的贡献,得出当Ni原子取代Fe原子时将优先占据Fe(3f)格点位置;根据第一性原理对能态的计算发现,不考虑磁性时不同格点P的pDOS未占据态电子结构与P-K近边吸收谱实验相符合;与考虑铁磁性Fe₂P 的DOS相比较后结果显示Fe₂P的磁性主要来源于Fe(3g)格点,铁磁性Ni₂P计算的Ni不同格点原子磁矩均接近于0,与它一般显顺磁性结论相一致. 关键词： X射线近边吸收谱 电子结构 多重散射理论 态密度     

Microstructure and optical absorption of Au-MgF2 nanoparticle cermet films

The microstructure and optical absorption of Au-MgF2 nanoparticle cermet films with different Au contents are studied. The microstructural analysis shows that the films are mainly composed of the amorphous MgF2 matrix with embedded fcc Au nanoparticles with a mean size of 9.8-21.4nm. Spectral analysis suggests that the surface plasma resonance （SPR） absorption peak of Au particles appears at λ=492-537nm. With increasing Au content, absorption peak intensity increases, profile narrows and location redshifts. Theoretical absorption spectra are calculated based on Maxwell-Garnett theory and compared with experimental spectra.     

Ab initio study of structural,electronic and optical properties of ternary CdO1-xSex alloys using special quasi-random structures

The structural, electronic, and optical properties of binary CdO, CdSe, and their ternary CdO1 xSexalloys(0 ≤ x ≤ 1) in the rock salt and zinc blend phases have been studied by the special quasi-random structure(SQS) method. All the calculations are performed using full-potential linearized augmented plane wave plus local orbital’s(FP-LAPW+lo) method within the framework of density function theory(DFT). We use Wu–Cohen(WC) generalized gradient approximation(GGA) to calculate structural parameters, whereas both Wu–Cohen and Engel–Vosko(EV) GGA have been applied to calculate electronic structure of the materials. Our predicted results of lattice constant and bulk modulus show only a slight deviation from Vegard’s law for the whole concentrations. The obtained band structure indicates that for the rock-salt phase, the ternary alloys present semi-metallic behavior, while for the zinc blend phase, semiconductor behavior with direct bandgap is observed with decreasing order of x except for CdSe. Finally, by incorporating the basic optical properties, we discuss the dielectric function, refractive index, optical reflectivity, the absorption coefficient, and optical conductivity in terms of incident photon energy up to 14 eV. The calculated results of both binaries are in agreement with existing experimental and theoretical values.