FeGa3的晶体结构

本文用X射线粉末法测定了FeGa₃的晶体结构,FeGa₃属四方晶系。在20℃的点阵常数是:a=6.2628?,c=6.5559?。每晶胞包含四个化合式量。空间羣为D_4h¹⁴——P4₂/mnm。Fe原子占据在4(f)等效位置上,Ga原子占据在4(c)及8(j)等效位置上;参数为:x_f=0.343,x_j=0.157,z_j=0.264。从结构看来,这是金属互化物的一种新类型。     

V2Ga5的晶体结构

本文利用单晶与粉末衍射方法测定了V₂Ga₅的晶体结构。V₂Ga₅属四方晶系,其单相区约为VGa₂—V₂Ga₅。在18℃的点阵常数是a=8.9540?,c=2.6892?,每个晶胞含有二个化合式量,空间羣为D_4h⁵—P4/mbm。V原子与Ga原子分别占据在4(h)与8(i),2(d)的等效位置上。参数为:x相似文献   

对称元素在解释帕脱逊图中的应用

这篇文章是介绍一种新的解释帕脱逊图的方法,利用这个方法可以测定无重原子的晶体结构。应用这方法来测定乙二胺四乙酸的晶体结构,我们得到了一个很好的结果。乙二胺四乙酸的晶体属单斜晶系,空间群是C_2h⁶,晶胞参数为a=13.28?;b=5.64?,c=16.14?和β^*=83°45′。在(hol)方向投影的平面群为P₂。每个单胞中有四个对称中心。     

乙二胺四乙酸晶体结构的测定

乙二胺四乙酸的晶体结构,已经利用对称元素的方法测定,晶体属单斜晶系,空间羣为C_2h⁶,晶胞参数各为a=13.28?,b=5.64?,c=16.14?及β^*=83°45′,每个单胞中有四个分子。原子间的距离已计算出来,并加经讨论。从晶体结构来看,乙二胺四乙酸的两个羧基与两个氮原子形成分子内部的氢键。因此,乙二胺四乙酸只表现出二元酸的性质,分子的结构式应写成:     

胺三乙酸银晶体和分子结构的测定

(CH₂COOH)₂NCH₂COOAg属于单斜晶系,单位晶胞中包含有四个分子,晶胞周期为α=7.61₁?,b=4.98₄?,c=23.25?,β=104°52′。空间羣为P2₁/c(C_2h⁵)。用柏特森及电子密度函数方法获得了原子坐标。键长C—C=1.51?,N—C=1.48?,C—O=1.28?及Ag—O=2.23—2.73?。指出了在分子之间具有较强的氢键O…O=2.54?。     

Fe-Ga二元系平衡图

本文主要从X射线的研究,并配合差热分析,测定了1000℃以下的Fe-Ga二元系平衡图。这一系统在室温存在着三个居间相ε,χ和Ψ。ε相是有序面心立方结构,相当于理想化合式Fe₃Ga,相区范围很窄。在550℃上下,这个相转变为另一相ξ,这是在高温从Ga在Fe中的固溶体直接分出来的,这个高温相的结构尚未测定。χ相的均匀范围较大,在室温从55at.％Ga延伸到60at.％Ga,结构似乎非常复杂,可能的化合式是Fe₄Ga₅,Fe₃Ga₄或Fe₂Ga₃,这是在960℃上下由包晶反应形成的。Ψ相由另一包晶反应形成,反应温度为820℃,Ψ相属四方晶系,在20℃,α=6.2628?,c=6.5559?,空间群为D_4h¹⁴-P4₂/mnm,晶包内含四个化合式量FeGa₃。没有观察到Fe在Ga中有任何固溶度。从FeGa₃到Ga,存在着一条共晶等温线,共晶点非常接近纯Ga,在约590℃,存在着一条共析等温线,共析点在50at.％Ga左右,在这里Ga在Fe中的固溶体同时分解成ξ和χ。这个系统中最值得注意的是Ga在Fe中的原生固溶体。在室温的固溶度是15.2at.％,它随温度而逐渐递增,在700℃以上,则突增到约50at.％,在625℃以下的结构是体心立方体,在相图中用α代表。但在625℃以上,这个相又转变为两个不同的结构,并且各占据着一定的相域,在相图中各用α₁和α₂代表。α₁和α₂的结构尚未经测定,最可能是从α结构导生的、由基本单胞依照一定规律堆垜起来而产生的原子的重新排列或空位缺陷。     

Mn_3Ga的晶体结构

本文用X射线粉末法,测定了Mn_3Ga的晶体结构。Mn_3Ga属六角晶系。26.8at.%Ga的合金在20℃的点阵常数是:a=5.4065A,c=4.3537A,c/a=0.8053。空间群为D_(6h)~4/mmc。每个单胞含两个化合式量,其中6个Mn原子占据6(h)的位置,原子参数x_h=0.837,2个Ga原子占据2(c)的位置。这是一个畸变型的DO_(19)有序密堆积超结构。Mn-Ga采内相当于这个结构的均匀范围并不包括理想成分在内,而偏移在富Ga的一边。     

含铋层状结构铁电体PbBi4Ti4O15和SrBi4Ti4O15的X射线衍射数据的测定

用衍射仪和Guinier聚焦相机收集了含秘层状结构铁电体PbBi₄Ti₄O₁₅SrBi₄Ti₄O₁₅的X射线粉末衍射图谱(Cu K_a),给出了d值大1.13?的88和76条衍射线的衍射数据和指标。它们都属正交晶系,空间群Bb2₁m(C_2v¹²),点阵常数和X射线理论密度为PbBi₄Ti₄O₁₅α=5.431?,b=5.459?,c=41.36?; z=4;D_x=7.986g/cm³.SrBi₄Ti₄O₁₅:α=5.428?,b=5.438?,c=40.94?;Z=4;D_x=7.447g/cm³.     

MnxSny(x=2,3,4; y=18,24,30)团簇几何结构的密度泛函研究

采用密度泛函方法,研究了Mn_xSn_y(x=2,3,4; y=18,24,30)团簇的几何结构. 发现Mn_xSn_6x+6(x=2,3,4)倾向于形成 Mn 原子内掺入D_3d Sn团簇单笼结构,即Mn₂Sn₁₈, Mn₃Sn₂₄ 和Mn₄Sn₃₀.而Mn_xSn_6x+12(x=2,3)则倾向于形成由两个小笼连接 而成的双笼结构,即MnSn₁₂-MnSn₁₂ 和MnSn₁₂-Mn₂Sn₁₈.因此,可望通过控制掺杂Mn 原子的数量来组装成不同结构的Mn_xSn_y一维纳米线.     

Magnetic properties of TbMn6Sn6-xGax (x=0.0－1.2) compounds

Effects of Ga substitution for Sn on the structure and magnetic properties of TbMn₆Sn_6-xGa_x (x=0.0－1.2) compounds have been investigated by means of x-ray diffraction, magnetization measurement and ¹¹⁹Sn M?ssbauer spectroscopy. The substitution of Ga for Sn results in a decrease in lattice constants and unit-cell volumes. The magnetic ordering temperature decreases monotonically with increasing Ga content from 423 K for x=0.0 to 390 K for x=1.2. At room temperature, the easy magnetization direction changes from the c-axis to the ab-plane. This variation implies that the substitution of Ga for Sn leads to a decrease in the c-axis anisotropy of the Tb sublattice. An increase in the non-magnetic Ga concentration results in a monotonic decrease of the spontaneous magnetization M_s at room temperature. Since there are three non-equivalent Sn sites, 2c (0.33, 0.67,0), 2d (0.33, 0.67,0.5) and 2e (0,0,0.34) in the TbMn₆Sn_6-xGa_x compounds, the ¹¹⁹Sn M?ssbauer spectra of the TbMn₆Sn₆ and TbMn₆Sn_5.4Ga_0.6 compounds can be fitted by three sextets. The hyperfine fields (HFs) decrease in the order of HF(2d)>HF(2e)>HF(2c), which is in agreement with the magnetic structure.     

两种新的SiC高层多型体——417R和453R

本文根据倒易点阵原理,详细分析了碳化硅劳埃照相中各种SiC三方多型体斑点和SiC基本类型6H斑点间的相互配置关系。这种关系共总结出不外乎十二种,本文提出利用这种关系,以及两6H类型斑点(hOl)间未知三方多型体的斑点数目,来计算未知多型体类型层数的方法。利用这一方法,对在实验室条件下以升华法制备的若干碳化硅单晶体进行了分析,发现了两种同时与6H类型连生的新的碳化硅高层多型体417R和453R,其空间群为R3m(C_3v⁵),点阵参数以六方晶胞表示时为 417R:α_H=3.0806?,c=1050.7?,z=417; 453R:α_H=3.0806?,c=1141.4?,z=453。以三方晶胞描述时则为 417R:α_R=350.4?,α=30.4′,z=139; 453R:α_R=380.6?,α=27.8′,z=151。     

The hyperfine properties of iron-gallium alloys

The hyperfine properties at Fe site in iron-gallium alloy are calculated using the full-potential linear-augmented-plane-waves method. We have calculated the Fermi contact field (B_hf) and isomer shift (δ) at the Fe site versus the number of neighbouring Ga atoms. We found that B_hf decrease whereas δ increases with increasing number of neighbouring G atom. In addition we have calculated the hyperfine properties of FeGa system with DO₃ structure, where various distributions of 4 the Ga atoms in the conventional unit cell are considered (including the regular DO₃ structure). We found that the DO₃ structure has the lowest energy as compared to the other configurations. The two distinct A and D sites of the ordered DO₃ conventional unit cell have two distinct values for B_hf and δ. On changing the atomic arrangement of the Ga atoms within the conventional unit cell, the configuration of the A site is maintained whereas that of the D site becomes imperfect. The contact magnetic hyperfine fields of the D-like sites in the imperfect structures are lower than that of the DO₃D site.     

碘酸镁晶体的结构与相变

本文用差热分析、高温和室温X射线衍射分析等方法研究了Mg(IO₃)₂·4H₂O的相变过程: Mg(IO₃)₂·4H₂O晶体属单斜晶系,空间群为P2或Pm,每个晶胞含有两个化合式量,点阵常数为a=8.307?,b=6.627?,c=8.541?,β=1.00°45′。我们用X射线粉末法测定了α-Mg(IO₃)₂的晶体结构。α-Mg(IO₃)₂属六角晶系,其空间群是P6₃。在14℃的点阵参数为a=5.4777?,c=5.1282?,c/a=0.9362。每个单胞含一个化合式量,6O^II占据在6(c)等效位置上,21^V占据在2(b)等效位置上,Mg⁺⁺无序地占据着2(a)等效位置的一半。其原子参数为x_c=0.096,y_c=0.344,z_c=0.162,z_b=0,z_a=0.981。从结构来看,它与α-LiIO₃同晶型,所不同的是2(a)位置只有一半被Mg⁺⁺离子占据着,另一半为空位。 关键词：     

Phonon spectra and lattice dynamics of lithium nitride

Lithium nitride, Li₃N, belongs to the hexagonal structure with the symmetry point group D_6h. The structure is ionic with four atoms per unit cell and N^3- coordinated in a regular way with eight Li⁺ ions. Polarized Raman scattering and infrared reflectivity spectra are reported. The frequencies of zone center phonons are determined from a Kramers-Kronig analysis and the oscillator fits to the reflectivity data. A rigid shell model with eight parameters, including the anisotropic polarizability of nitrogen ions, yields an excellent fit to the observed phonon frequencies.     

The crystal structure of ammonium metavanadate

The paper deals with the structure analysis of ammonium metavanadate NH₄VO₃ from photographs obtained with a Weissenberg goniometer using CnKand MoKradiation. The dimensions of the orthorhombic unit cell determined from these photographs of the rotating crystal are a=4.92, b=11.82, c==5.85 Å. A satisfactory space group is Pbcm (D _2h ¹¹ ),with four molecules in the unit cell. The positions of the atoms in the unit cell were determined by means of the Patterson functions P(v, w), P(u, v) and from the projection of the electron density on the (001)plane. An analogy was found with the structure of the metasilicates from the pyroxen group. The oxygen atoms are coordinated tetrahedrally around the vanadium atoms. The tetrahedra VO₄ form infinite chains in the direction of the [001]axis. The VO₄ chains are mutually bonded by means of electrostatic bonds of the NH₄ ions. The splitting of the chains in an aqueous solution is connected with the dissociating and catalytic properties of the ammonium metavanadate.In conclusion we should like to thank the management of the Institute of Technical Physics of the Czechoslovak Academy of Sciences for enabling us to work on this problem.