共查询到18条相似文献,搜索用时 171 毫秒
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氟碳铈钡矿Ce2Ba3(CO3)5F2是在我国发现的新矿物,其电子衍射斑点按强度可分为两大类:较强的一类是晶体亚结构的贡献;其余衍射斑点是超结构的贡献。晶体的亚结构与黄河矿的相类似,可以划出一个六角的亚晶胞。亚晶胞参数为a0=5.06?,c0=9.63?。超结构属单斜晶系,晶胞参数为a=21.2?,b=5.06?,c=13.1?,β=95°。晶体属空间群C2/m、Cm或C2,亚结构与超结构的基矢有如下关系:该矿h00系统衍射形成的晶格象中,常夹有间距较小的条纹,或宽的黑带。本文对此进行了讨论,也讨论了该矿是否会有更大周期的超结构问题。
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利用透射电子显微镜对Ni67Zr33非晶合金晶化的研究发现了两个新的亚稳相T0与T10。其中T1相为体心正交(准四方〕晶体,点阵常数a≌b=0.89nm,c=3.14nm,空间群为Iba2或Ibam。温度升高,T1相转变为含有大量错排的A心正交Ni10Zr2相,用1/2(a+b)位移错排模型可以圆满地解释其电子衍射图中仅h+k为奇数的衍射斑沿c*方向拉长的现象,晶化稳定相为Ni10Zr,与Ni21Zr8(Ni5Zr2)相。
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黄河矿是在我国发现的一种钡铈氟碳酸盐新矿物,其理想化学式为BaCe[Fl(CO3)2],本矿物属三方晶系,利用四圆衍射仪收集强度数据,测得α=b=5.070(±0.003)?,c=38.408(±0.005)?,空间群为R3m. z=6,本文在前人工作的基础上,对该矿物进行了较为精确的测定,最后的偏离因子R=0.041。本文还对黄河矿赝结构及超结构的关系作了探讨,与前人工作进行了对比,对类似矿物的修正方案提出看法,对个别实验数据作了讨论。
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本文用X射线粉末法测定了Li2K(IO3)3与Li2NH4(IO3)3的晶体结构和原子参数。发现Li3K(IO3)3,Li2NH4(IO3)3与Li2Rb(IO3)3同晶型,属单斜晶系,空间群为P21/α,每个单胞含有四个化合式量。室温的点阵常数分别为α=11.198?,b=11.046?,c=8.254?,β=111.53°,及α=11.327?,b=11.078?,c=8.341?,β=111.87°。讨论了二元化合物的形成与离子半径的关系。
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M. Amara R. M. Gal ra P. Morin T. Veres P. Burlet 《Journal of magnetism and magnetic materials》1994,130(1-3):127-132
Among the AuCu3-type RIn3 series where R is a rare earth, the NdIn3 compound presents a complex magnetic phase diagram. In this compound, which orders antiferromagnetically at TN = 5.9 K, three magnetic phases are separated by two sharp first-order transitions. The phase diagrams, determined for the main crystallographic directions, by magnetization measurements in fields up to 7 T show a strong dependence of the transition temperatures. In order to determine the actual magnetic structures in NdIn3, a neutron diffraction experiment has been performed on a single crystal under magnetic field. It shows that the magnetic structures are collinear (single q) with the magnetic moments aligned along the fourfold axis. They clearly evidence the existence of two incommensurate phases with q = (1/2, 1/2, τ): for TN T 5.5 K, τ1 ≈ 0.037 2π/a and the structure is sine-wave modulated, for 5.5 K > T > 4.7 K, τ2 = 0.017 2π/a and the structure squares up. Below 4.7 K the q = (1/2, 1/2, 0) commensurate structure is stabilized. 相似文献
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P. Schobinger-Papamantellos J. Rodríguez-Carvajal G. Andr K. H. J. Buschow 《Journal of magnetism and magnetic materials》1995,150(3):311-322
The magnetic ordering of the hexagonal compound TbMn6Ge6 has been studied by neutron diffraction at various temperatures between 1.8 and 500 K. In almost the whole magnetically ordered regime the magnetic structures are incommensurate with the crystal lattice. The corresponding wave vector q1 = (0,0,qz) is strongly temperature dependent and decreases from qz = 0.1307 r.l.u. at 1.8 K to qz = 0.091 r.l.u. at 410 K. The low-temperature range (T < 85 K) is characterised by a triple ferrimagnetic spiral structure with net moment along the c-direction. At Tt = 85 K the net moment disappears and the magnetic ordering changes into a flat spiral structure that probably persists up to the magnetic ordering temperature, TN = 450 K. Before reaching the magnetic ordering temperature, however, an additional ferrimagnetic component perpendicular to the c-direction develops, marking the onset of re-entrant ferrimagnetism. The resulting structure described by two propagation vectors corresponds to a distorted spiral. Various models are discussed. The observed re-entrant ferrimagnetism is in agreement with results of previously reported magnetic measurements. 相似文献
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P. Schobinger-Papamantellos K.H.J. Buschow 《Journal of magnetism and magnetic materials》1994,130(1-3):242-246
The magnetic ordering of the orthorhombic compound CeSi (Pama space group, FeB type of structure, Z = 4) Tn = 5.6 K was investigated by means of powder neutron diffraction in the temperatures 1.5 and 10 K. Our results show that the magnetic ordering is associated with a three dimensionally amplitude-modulated phase which is incommensurate with the crystal lattice with wave vector q = (qχ,qy,qz). The ordered Ce3+ moments are confined to the plane (a,b) at an angle of 16.7° with the b direction. It follows from the present data analysis that the dominant wave vector component is qz, which approximately corresponds to a transversal modulation, however the incommensurateness involves also the qx and qy components. The amplitude of the sine wave is μ0j = 1.667μB at 1.5 K which corresponds to quite a reduced ordered moment value compared to the Ce3+ free ion value gJ = 2.14μB. 相似文献
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Misfit layer compounds of the type (NdS)nNbS2 have been made by iodine vapour transport. They have been characterised by energy dispersive X-ray analysis, transmission electron microscopy and electron diffraction. An orthorhombic form with Am2m symmetry has been observed. The unit cell contains two layers of NdS and two layers of NbS2. The layers have rectangular symmetry and are stacked alternately with their planes perpendicular to the c-axis. A curious feature of the structure is that the layers have a common b unit cell parameter but the a values, which depend on the metal element in a given layer, are incommensurate. The lattice parameters for the material are a = 0.5625 nm for the NdS layer, a = 0.331 nm for the NbS2 layer, b = 0.5733 nm and c = 2.266 nm. The symmetry of the material observed in the present work is Am2m which differs from the Fm2m reported by others. It is argued that the lower symmetry occurs because of a displacement of Nb atoms in one of the layers in the unit cell. A comparison between calculated and observed electron diffraction patterns and energy arguments are used to support the proposed explanation. 相似文献
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W. T. Fu H. W. Zandbergen Q. Xu J. M. van Ruitenbeek L. J. de Jongh G. van Tendeloo 《Solid State Communications》1989,70(12):1117-1121
A series of new compounds Ba4(Pb1−xBix)3O10 with 0≤x<0.3 has been prepared and characterized by X-ray and electron diffraction. The d.c. resistivity vs. temperature data for different x values are presented and structural features are compared to those of the superconducting phase Ba(Pb1−xBix)O3. The “mother-compound” Ba4Pb3O10 is tetragonal, with lattice constants A=0.4280(1) and C=3.017(1) nm. Its structure can be regarded as a stacking of Ba(PbBi)O3 triple-layers, separated by single BaO layers. Electron diffraction reveals the presence of a weak superstructure with the a-axis related to that of the perovskite by a=√2ap. Frequent intergrowth of this phase with the perovskite structure is observed. The conductivity of the samples Ba4Pb3O10 is nearly independent of temperature, while Bi-doped samples exhibit semiconductor-like behaviour at low temperature. No superconducting transition is observed down to 2K. 相似文献
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本文构建了一种包含石墨烯和亚波长光栅的复合结构, 借助衍射光栅的导模共振效应, 在石墨烯表面激发高局域性表面等离子体激元, 研究了石墨烯与光栅结构对表面等离子体激元局域特性的影响规律, 并借助基于有限元法的COMSOL软件, 分析了缓冲层厚度、光栅周期、载流子迁移率和费米能级对石墨烯的表面电场、品质因子Q和有效模式面积Seff的影响. 结果表明, 石墨烯表面等离子体激元的局域性在特定的参数点获得显著提高: 当μ = 0.7 m2/(V·s)时, 品质因子达到最大值Qmax = 1793; 当p = 235 nm或EF = 0.72 eV时, 表面电场达到了入射光的3000倍以上. 强烈的局域性导致强烈 的光-物质相互作用, 因而本文提出的复合结构可实现高灵敏度传感器和高效率的非线性光学设备, 极大地扩展了石墨烯在纳米光学领域中的应用. 相似文献
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