BiFeO3纳米粉的制备、结构表征及铁磁特性

采用溶胶-凝胶法成功地制备出BiFeO₃纳米粉,利用X射线衍射仪（XRD）、扫描电子显微镜（SEM）和透射电子显微镜（TEM）测量分析了其结构与形貌,结果发现：胶体经700℃烧结2—25 h后,形成了30 nm左右的较纯相BiFeO₃粉末,该样品为六角晶系,R3-m［166］空间群,晶胞参数为a=b=05580 nm,c=06939 nm,其（101）面晶面间距为0396 nm左右,（ 关键词： 溶胶-凝胶法 3纳米粉')" href="#">BiFeO₃纳米粉 结构表征 铁磁特性     

关于Zn1-xBexO电子结构和光学性质的研究

采用基于密度泛函理论和平面波赝势技术的CASTEP程序对Zn_1-xBe_xO合金电子结构和光学性质进行了计算.当0≤x≤1,其带隙从0.963 eV变化到7.293 eV.分析了晶格畸变和能带间排斥效应对带隙的影响.当Be含量x=0.125,0.25,0.375,0.5,0.625,0.75时,a/b轴压应变控制着带隙变化;当x=0.875,1时,c轴压应变控制着带隙变化.能带间的p-d排斥影响价带顶变动,Γ_1v与Γ_1c之间排斥影响导带底变动.这些能带间的排斥效应被用来分析Zn_1-xBe_xO带隙变动.另外,也分析了Zn_1-xBe_xO介电函数虚部ε₂. 关键词： 带结构 光学性质 应变 排斥     

Fe的结构与物性及其压力效应的第一性原理计算

采用基于密度泛函理论的平面波赝势方法，计算了Fe的几种不同晶体结构的总能量曲线，对HCP结构下晶体结构参数c/a随压强的变化关系做计算分析. 能量计算精度取为0.01 eV/atom. 计算得出： 1) 零温下Fe从bcc到hcp结构的相变压强约为15 GPa，与实验结果相一致； 2) 压强的升高会导致Fe的磁矩减小，最终破坏Fe的磁性； 3) 压强升高引起hcp晶体结构参数c/a缓慢增大，而在地核压强(135—360 GPa)范围内，c/a取常量约1.59能够满足计算精度的要求. 关键词： 第一性原理计算 压力效应 Fe的结构与物性     

Si在TiAl3中取代行为的第一性原理研究

采用基于密度泛函理论的第一性原理方法,研究了Si原子在TiAl₃中的格点取代行为.通过对不同原子被置换后的c/a值、形成能以及电子态密度的计算和比较,发现Si原子倾向于取代TiAl₃中的Al原子,其取代行为主要由系统的电子结构决定,计算结果与实验相符.为了进一步研究Si原子的取代行为,对Si原子占据的格点以松散或紧凑分布下体系的总能、形成能以及电子态密度进行了计算,结果表明Si原子倾向于取代TiAl₃中松散分布的Al（2）原子.对c/a值的计算表明,随Al（2）格点Si原子浓度的增加,c/a值逐渐增大;而当Si取代Al（1）格点时,c/a值随Si原子浓度的增加而减小.研究表明,Si在TiAl₃中的极限固溶度介于12.5at%—18.75at%之间. 关键词： 密度泛函理论 第一性原理 电子结构 3')" href="#">TiAl₃     

FeTe合金结构分析及其薄膜制备

利用固态反应法制备了名义成分为FeTe的合金, 采用X射线粉末衍射技术和Rietveld全谱拟合分析方法测定了其相组成和晶体结构. 研究表明,主相为Fe_1.08Te,空间群为P4/nmm,点阵参数 a = 3.8214(3) Å, c = 6.2875(3) Å, Z = 2, Fe原子占据2a和2c晶位, Te原子占据2c晶位. 利用脉冲激光沉积技术制备的FeTe薄膜超导转变起始温度为13.2 K,零电阻温度为9.8 K. 关键词： FeTe Rietveld结构精修 超导薄膜     

BiTiO3电子结构及光学性质的第一性原理研究

采用基于第一性原理的赝势平面波方法, 对BiTiO₃的多种结构进行了计算. 计算结果表明, C1C1结构最为稳定, 对应晶格参数为a=b=5.606 Å, c=9.954 Å; α=β=105.1°, γ=61.2°. 进一步对C1C1结构的BiTiO₃的能带结构、电子性质和光学性质进行了研究, 发现BiTiO₃是间接带隙半导体, 其费米面附近的能带主要由Ti-3d和O-2p层的电子态构成. 通过介电函数、复折射率和反射率等的研究, 发现BiTiO₃的光学性质为近各向同性.     

利用金属有机物化学气相沉积技术生长的a面GaN表面形貌和位错的研究

采用金属有机物化学气相淀积技术在r面蓝宝石衬底上制备了a面GaN薄膜,用熔融的KOH在400 ℃对样品分别腐蚀1.0,1.5和2.0 min.用扫描电镜、原子力显微镜、X射线衍射谱和阴极射线荧光对腐蚀前后的表面形貌进行分析.研究表明,400 ℃下腐蚀1.5 min后出现了长平行四边形的条纹状,这是由于无极化的a面GaN表面极性各向异性,c向与m向上N原子悬挂键密度不同,同时稳定性不同,对OH^-离子的吸附能力不同造成的,其中沿c方向易于腐蚀.同时,a面GaN腐蚀后出现了六角突起.我们认为这与穿透位错有关,而其形貌则与GaN薄膜的位错局部极性有关. 关键词： a面GaN')" href="#">a面GaN 堆垛层错 极性     

Al的微观组态与LaNi3.75Al1.25的结构和弹性第一性原理研究

在全电子水平上，采用广义梯度近似密度泛函理论和全势能线性缀加平面波方法并结合二维立方拟合方法，对LaNi_3.75Al_1.25合金的晶体结构与弹性性质进行了理论研究.计算结果给出合金的晶格常数a=b=0.5137　nm，c=0.4018　nm，Al原子在晶胞中的微观分布为同时占据部分3g和2c等价格位，弹性常数C₁₁+C₁₂=281.2，C₁₃=82.3，C₃₃=227.3，以及体弹性模量B＝124.5、切变模量G＝68.2　GPa.还对态密度、能带结构和电荷密度进行了计算分析，并给出材料LaNi_3.75Al_1.25的电子线性比热系数23.45　mJ/molK². 关键词： 3.75Al_1.25')" href="#">LaNi_3.75Al_1.25 储氢合金 全势能线性缀加平面波 弹性常数     

C60单晶的表面形貌与生长缺陷

用气相法生长出了毫米尺寸的具有规则晶面和金属光泽的高质量的纯C₆₀单晶.X射线衍射分析表明,C₆₀单晶在室温下具有面心立方(fcc)结构,晶格常数为α=1.4199(4)nm。用扫描电子显微镜和光学显微镜观察了C₆₀单晶的形貌,除观察到fcc结构的晶体所特有的{111}和{200}两种稳定晶面以及非常容易形成的孪晶之外,还发现了在{111}面上的树枝状、垄状和生长丘以及在{200}面上的树枝状、游泳池状和生长丘的生长缺陷。对C_{60 关键词：}     

不同晶面银纳米晶高温熔化的各向异性

采用嵌入原子势, 使用分子动力学方法, 模拟研究了银纳米晶高温弛豫过程中的热稳定性和熔化机制, 并引入均方位移和稳定寿命来分析它的结构和形状的演化过程. 结果表明: 对于沿相互垂直{110}, {211}和{111}面切割形成的近正方体截面纳米晶, 高温弛豫熔化存在明显的各向异性行为; (112) 面热稳定性最低, 最易熔化, 其次是(110) 面, 热稳定性最高的是(111) 面, 最难熔化; 三个不同晶面的最外层和次外层原子的稳定寿命极短, 且三个不同晶面之间相差很小, 没有明显差异; 对于具有相同晶面指数的晶面, 第三层及其以内的稳定寿命较长, 且依次微量增长, 但不同晶面第三层及其以内的寿命相差明显.     

Anomalous magnetotransport phenomena in θ-(BEDT-TTF)2I3

Anomalous magnetotransport phenomena have been observed in θ-(BEDT-TTF)₂I₃ crystals at temperatures below 15 K. The magnetoresistance M : (1) is a linear function of the magnetic field H, (2) is not affected by the angle between the electric current and the magnetic field, (3) but depends on the magnetic field orientation with respect to the crystal axis. Magnetoresistance is expressed as M = (aH²_a + bH²_b + cH²_c)₀^-3/2/H in terms of H = (H_a, H_b, H_c), the zero field resistivity ₀, and parameters a, b, and c which are independent of temperature and magnetic field. We have found that b a > c. Magnetoresistance up to 40 is observed for H = 7T along the b-axis at T = 1.5K.     

Phase transitions in 1,3,4-oxadiazole crystals under high pressure

Crystalline 2,5-di(4-nitrophenyl)-1,3,4-oxadiazole (DNO) has been investigated at pressures up to 5 GPa using Raman and optical spectroscopy as well as energy dispersive X-ray techniques. At ambient pressure DNO shows an orthorhombic unit cell (a=0.5448 nm, b=1.2758 nm, c=1.9720 nm, density 1.513 g cm⁻³) with an appropriate space group Pbcn. From Raman spectroscopic investigations three phase transitions have been detected at 0.88, 1.28, and 2.2 GPa, respectively. These transitions have also been confirmed by absorption spectroscopy and X-ray measurements. Molecular modeling simulations have considerably contributed to the interpretation of the X-ray diffractograms. In general, the nearly flat structure of the oxadiazole molecule is preserved during the transitions. All subsequent structures are characterized by a stack-like arrangement of the DNO molecules. Only the mutual position of these molecular stacks changes due to the transformations so that this process may be described as a topotactical reaction. Phases II and III show a monoclinic symmetry with space group P2₁/c with cell parameters a=1.990 nm, b=0.500 nm, c=1.240 nm, β=91.7°, density 1.681 g cm⁻³ (phase II, determined at 1.1 GPa) and a=1.890 nm, b=0.510 nm, c=1.242 nm, β=89.0°, density 1.733 g cm⁻³ (phase III, determined at 2.0 GPa), respectively. The high-pressure phase IV stable at least up to 5 GPa shows again an orthorhombic structure with space group Pccn with corresponding cell parameters at 2.9 GPa: a=0.465 nm, b=1.920 nm, c=1.230 nm and density 1.857 g cm⁻³. For the first phase a blue pressure shift of the onset of absorption by about 0.032 eV GPa⁻¹ has been observed that may be explained by pressure influences on the electronic conjugation of the molecule. In the intermediate and high-pressure phases II–IV the onset of absorption shifts to increased wavelengths due to larger intermolecular interactions and enhanced excitation delocalization with decreasing intermolecular spacing.     

一种简单高效的制备硅纳米孔阵结构的方法

本文介绍了一种简单高效的制备硅纳米孔阵结构的方法. 利用激光干涉光刻技术, 结合干法和湿法刻蚀工艺, 直接将光刻胶点阵刻蚀为硅纳米孔阵结构, 省去了图形反转工艺中的金属蒸镀和光刻胶剥离等必要步骤, 在2英寸的硅 (001) 衬底上制备了高度有序的二维纳米孔阵结构. 利用干法刻蚀产生的氟碳有机聚合物作为湿法刻蚀的掩膜, 以及在干法刻蚀时对样品进行轻微的过刻蚀, 使SiO₂点阵图形下形成一层很薄的硅台面, 是本方法的两个关键工艺步骤. 扫描电子显微镜图片结果表明制备的孔阵图形大小均匀, 尺寸可控, 孔阵周期为450 nm, 方孔大小为200–280 nm. 关键词： 激光干涉光刻 纳米阵列 刻蚀 氟碳有机聚合物     

Formation and decay kinetics of nickel nitrides resulting from nitrogen ion implantation. The nickel–nitrogen phase diagram

Structural transformations in nickel films exposed to N⁺ ions were investigated through the use of electron diffraction, electron microscopy, Rutherford backscattering (RBS) of He⁺ ions, thermal desorption spectroscopy (TDS).

With an increasing exposure dose, there occurred a smooth transition of the FCC structure of Ni to the HCP phase -Ni₃N with the lattice parameters a=0.266 nm and c=0.430 nm. The completion of the transition was observed once the implanted nitrogen concentration corresponding to the stoichiometric ratio of Ni₃N was attained, this giving evidence for the chemical nature of the structural change observed.

During annealing, structure variations were traced, enabling one to observe the following four nickel nitrides: (1) -Ni₃N with a disordered arrangement of nitrogen atoms (HCP-phase with a=0.266 nm and c=0.430 nm), (2) β-Ni₃N with an ordered arrangement of nitrogen atoms (two hexagonal lattices: one with a=0.266 nm, c=0.430 nm, and the other with a=0.466 nm and c=0.43 nm), (3) Ni₄N having a primitive cubic lattice structure with a=0.377 nm, (4) Ni₈N having the FCC structure with a=0.725 nm.

The results of an investigation have led to building up a phase diagram for the Ni–N system.     

Crystal structure and phase transitions of [(C2H5)4N]6Bi8Cl30

A new [(C₂H₅)₄N]₆Bi₈Cl₃₀ crystal of the family of alkylammonium halogenobismuthates was grown. X-ray diffraction studies showed that the crystals are monoclinic, space group C2/m with a = 20.117(5), b = 12.682(3), c = 20.396(5) Å, β = 93.03(3), Z =2. The lattice consists of (C₂H₅)₄N⁺ cations and a new type of Bi₈Cl⁶⁻₃₀ anion. Dielectric studies revealed two closely-lying structural phase transitions around 241 K (on cooling). They were interpreted as due to a freezing of the rotational motions of tetraethylammonium cations.     

基于介质环形柱结构的二维光子晶体中Dirac点的实现

利用偶然简并方法在二维正方格子介质环形柱结构光子晶体中成功实现了Dirac点, 并利用平面波展开法对实现Dirac点的过程进行了研究. 研究结果表明, 对于二维正方格子介质环形柱结构光子晶体, 在一定的外径R_O范围内(0.37a<R_O<0.5a), 当Dirac点存在时(n>1.4), 介质环内径R_I与外径R_O满足一个不随介质环折射率n变化的恒定关系式. 同时, Dirac点对应的光子约化频率f随折射率n及外径R_O的增大而减小. 利用所得的关系式对特定介质环折射率n条件下能实现Dirac点的环形光子晶体进行了预判设计.     

Two types of the effective mass divergence and the Grüneisen ratio in heavy-fermion metals

The behavior of the specific heat c_p, effective mass M^*, and the thermal expansion coefficient of a Fermi system located near the fermion condensation quantum phase transition (FCQPT) is considered. We observe the first type behavior if the system is close to FCQPT: the specific heat , , while the thermal expansion coefficient . Thus, the Grüneisen ratio Γ(T)=/c_p does not diverges. At the transition region, where the system passes over from the non-Fermi liquid to the Landau Fermi liquid, the ratio diverges as . When the system becomes the Landau Fermi liquid, Γ(T,r)∝1/r, with r being a distance from the quantum critical point. Provided the system has undergone FCQPT, the second type takes place: the specific heat behaves as , M^*∝1/T, and =a+bT with a,b being constants. Again, the Grüneisen ratio diverges as .     

X-ray and high resolution selenium-77 solid state NMR spectroscopy as complementary probes to structural studies of organophosphorus diselenides

high resolution solid state NMR spectroscopy was employed to study structural properties of bis(diisopropoxyphosphorothioyl) diselenide 1 and bis(dineopentoxyphosphorothioyl) diselenide 2. The principal elements T_ii of effective dipolar/chemical shift tensor were calculated from spinning sideband intensities employing the WIN-MAS program. The values of anisotropy and asymmetry parameters reflect the distortion of the selenium environment. It was found that the T₃₃ component mostly contributes to changes in the isotropic chemical shifts. CP/MAS experiments were used to decide the assignment of space group by counting the number of crystallographically unique selenium centers in the unit cell. Crystals of diselenide 1 are triclinic, space group P with a=8.485(3) Å, b=8.508(1) Å, c=8.511(2) Å, =98.835(15)°, β=111.653(24)°, γ=93.524(21)°, V=559.5(3) ų, D_c=1.544(2) g/cm³ and Z=1. Refinement using 2222 reflections for 157 variables gives R=0.037. Crystals of diselenide 2 are triclinic, space group P1 with a=9.1418(8) Å, b=9.1465(8) Å, c=9.9200(9) Å, =74.751(8)°, β=74.629(7)°, γ=82.216(7)°, V=769.7(1) ų, D_c=1.365(2) g/cm³ and Z=1. Refinement using 3316 reflections for 297 variables gives R=0.0272.     

带多孔硅表面缺陷腔的半无限光子晶体Tamm态及其折射率传感机理

结合表面缺陷半无限光子晶体Tamm态与多孔硅光学传感机理,在光子晶体表面缺陷腔中引入多孔硅,并利用其高效的承载机制,提出基于多孔硅表面缺陷光子晶体Tamm态的折射率传感结构.在半无限光子晶体中缺陷腔与原来的周期性分层介质结构的界面上存在Tamm态,通过入射角度调制使其在缺陷腔中实现多次全反射,并在缺陷腔中加入吸收介质,使谐振波长在缺陷腔中完成衰荡,从而在反射谱中得到缺陷峰;调整光子晶体参数,使缺陷峰的半高全宽得到优化,提高其品质因数(Q值);在此基础上,根据Goos-H?nchen相位移与谐振波长的关系,建立由待测样本折射率改变所导致的多孔硅表面吸附层有效折射率变化与缺陷峰值波长漂移之间的关系模型,并分析其折射率传感特性.结果表明,此生物传感结构Q值为1429,灵敏度为546.67 nm/RIU,证明了该传感结构的有效性,可为高Q值和高灵敏度折射率传感器的设计提供一定的理论参考.