Crystal structure and magnetism of the Y2Pd14B5 compound

The crystal structure of the ternary boride Y₂Pd₁₄B₅, space group I4₁/amd, a=8.484(2) Å, c=16.490(3) Å, V=1186.98 ų, Z=4, was refined down to R=0.0475, wR2=0.1276 from single crystal X-ray diffraction data. Two types of coordination for boron atoms were observed: the coordination sphere for the B1 atom is a trigonal prism with one additional atom; the B2 atom has only four neighboring atoms which form a square. No boron–boron contact was observed. Analysis of the Y₂Pd₁₄B₅ crystal structure shows the existence of a correlation between this structure and the Sc₄Ni₂₉B₁₀ structure type. Magnetization and AC susceptibility measurements indicate that there is no superconducting or magnetic transition in Y₂Pd₁₄B₅ down to 2 K.     

An investigation of the structures of the compounds in the tin-rich part of the Dy–Sn system: Crystal structure of Dy5Sn11 and Dy5Sn13

The structural properties of the compounds in the tin-rich part of the dysprosium–tin system have been studied by X-ray powder diffraction. The crystal structures of six compounds DySn_2+x (0 < x < 1) have been characterized. There are four compounds with known structural types: DySn₂ with the ZrSi₂ structure, Dy₃Sn₇ with the Gd₃Sn₇ structure, Dy₂Sn₅ with the Er₂Ge₅ structure, DySn₃ with the DyGe₃ structure and two compounds characterized by new body-centred orthorhombic types (Immm): Dy₅Sn₁₁ (a = 4.411 Å, b = 42.50 Å and c = 4.328 Å) and Dy₅Sn₁₃ (a = 4.341 Å, b = 48.05 Å and c = 4.405 Å) which result from various insertions of AuCu₃ and Po slabs into the ZrSi₂ structure. The relationships and structural evolution are discussed.     

DD9镍基单晶高温合金固溶处理初熔组织研究

研究了DD9单晶合金固溶处理过程中组织的变化以及初熔组织的生成机理。结果表明,初熔组织分为两类,即γ/γ′共晶组织熔化生成的不规则初熔组织及固溶微孔熔化生成的规则初熔组织。初熔组织严重降低铸件的高温性能,在1100℃、137 MPa条件下,初熔组织使铸件的使用寿命缩短35h。两种初熔组织都可以通过延长较低温度下的保温时间,促进元素的扩散来消除。     

Phase relationships and crystallography in the pseudobinary system Gd5Si4---Gd5Ge4

A study of phase relationships and crystallography in the pseudobinary system Gd₅(Si_xGe_1−x)₄ revealed: (1) that both terminal binary compounds Gd₅Si₄ and Gd₅Ge₄ crystallize in the Sm₅Ge₄-type orthorhombic structure, and (2) the appearance of an intermediate (ternary) phase with a monoclinic crystal structure which is similar to both Gd₅Si₄ and Gd₅Ge₄. The formation of the monoclinic phase at 0.24≤x≤0.5 [between Gd₅(Si_0.96Ge_3.03)Gd₅(Si₁Ge₃) and Gd₅(Si₂Ge₂)] is probably due to the large difference in bonding characteristics of Si and Ge in the Gd₅Si₄-Gd₅Ge₄ pseudobinary system which limits the ability of the mutual substitution of Si for Ge and vice versa without a change of the crystal structure. For the composition Gd₅(Si₂Ge₂) the lattice parameters of the monoclinic structure (space group P112₁/a) are a=7.580865), b=14.802(1), c=7.7799(5)Å, γ=93.190(4)°. A distinct difference in the magnetic behaviors of the alloys from three different phase regions in this system follows the distinct difference in the crystal structures observed for the alloys from the three phase regions.     

Effect of superrapid crystallization on the structure and properties of maraging steels

Conclusion Super rapid crystallization of melts for maraging steels has a considerable effect on the nature of their phase transformation, structures, and properties. Depending on solidification rate and subsequent cooling it is possible to form in steel 01N17K12M5T structures of the following types: 1) entirely martensitic; 2) entirely ferritic; 3) a mixture of martensitic and austenitic components. The maximum microhardness is achieved with formation in the test steel of a highly dispersed entirely martensitic structure. An increase in the microhardness of martensitic structure is governed mainly by the small width of martensitic platelets. Results of experimental data are in good agreement with the Hall-Petch relationship, which points to the decisive role of the interface in metal strengthening.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 32–39, January, 1988.     

S=1/2 quantum Heisenberg antiferromagnet ladders

The synthesis, structure and powder magnetic susceptibility of two new copper complexes: [(2-amino-5-iodopyridinium)CuCl₃ and (2-amino-5-iodopyridinium)₂CuBr₄·2H₂O] are reported. Both the crystal structures and the powder magnetic susceptibility support the magnetic structure of the complexes as S=1/2 ladders.     

Synthesis of tetrapod-shaped ZnO whiskers and microrods in one crucible by thermal evaporation of Zn/C mixtures

Tetrapod-shaped ZnO whiskers and microrods were synthesized in one crucible by thermal evaporation of Zn/C mixtures at 930 ℃ in air without any catalyst. The digital camera, optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction techniques were used to study the morphologies and crystal structures of these tetrapod-shaped ZnO microcrystals. The results show that these two types of ZnO tetrapods are grown at different heights within the same crucible. The legs of these tetrapod-shaped ZnO crystals are hexagonally faceted. Some tetrapod-shaped ZnO whiskers show hierarchical structures. A short button-like hexagonal ZnO microcrystal is observed at the triple junctions of some tetrapod-shaped ZnO whiskers. The tetrapod-shaped ZnO microrods are capped by two sets of hexagonal pyramids with two different groups of crystal planes for the surfaces. These two types of tetrapod-shaped ZnO microcrystals have different side faces and aspect ratio, which are believed to be the result of their different growth behaviors. The octa-twin model was used to discuss the different growth behaviors of these two types of ZnO tetrapods. The crystal planes of the legs and the pyramids were determined.     

Y_3(Fe,M0)_(29)金属间化合物的结构特性

使用Rietveld方法对Y3（Fe,Mo）29金属间化合物的X射线衍射谱和中子衍射谱进行分析,得出了Y3（Fe,Mo）29金属间化合物属A2／m空间群的结论.坐标变换结果表明Y3（Fe,Mo）29金属间化合物的空间结构是1∶12和2∶17的混合结构     

Y3（Fe,Mo）29金属间化合物的结构特性

使用Ｒｉｅｔｖｅｌｄ方法对Ｙ３（Ｆｅ,Ｍｏ）２９金属间化合物的Ｘ射线衍射谱和中子衍射谱进行分析,得出了Ｙ３（Ｆｅ,Ｍｏ）２９金属间化合物Ａ２／ｍ空间群的结论。坐标变换结果表明：Ｙ３（Ｆｅ,Ｍｏ）２９金属间化合物的空间结构是１：１２和２：１７的混合特性。     

氧化锆（ZrO_2）的电、光性质与应用

重点分析了ZrO2的电子结构与能带特点、光学吸收、发射谱等,介绍了第一原理法计算不同晶相ZrO2的能带结构和电子能量状态密度图（DOS）的结果,在计算能级结构的基础上,归纳了不同晶相的ZrO2在禁带附近可能的电子跃迁机理及其相应的能量,说明了无论是高纯ZrO2还是掺杂ZrO2,在室温下均表现出高的绝缘性能。分析了高温下ZrO2导电能力提高的原因,高温导电性可应用于氧传感器和燃料电池中的电极隔膜材料。掺杂后的ZrO2晶体的透光性非常好,且在较高温度的环境中,如果不发生晶体结构转变或失透等,则温度对提高晶体的折射率有积极的作用。ZrO2粉体的白色外观是由于粉体的表面对可见光的散射以及晶体内部的大量缺陷对光的散射作用。介绍了纯ZrO2材料的发光效应来源在于捕获了电子的氧空位形成的新能级与基态能级间的跃迁,氧空位形成的F-色心或缔合中心而产生。指出ZrO2可以作为发光离子基质的原因在于作为宽禁带的ZrO2的声子能量较低,可为发光中心的稳定发光提供刚性场所。     

Crystalline structure of solution-processed pentacene thin films

We report on the crystalline structure of solution-processed pentacene thin films, prepared without using any precursors or derivatives. In these films, two types of surface structure were observed: flat domains and rough domains. The flat domains exhibited higher field effect mobilities than the rough domains and were composed of two-dimensional plate-like domains of several hundred micrometers containing large crystallites. The in-plane structures of the solution-processed thin films were analyzed by grazing-incidence X-ray diffraction (GIXD). The in-plane two-dimensional mapping of the GIXD patterns reveals that the solution-processed pentacene thin films have a crystal structure similar to that reported by Campbell et al. [Acta Crystallogr. 15 (1962) 289].     

Microstructural characteristics of Nb–Si based ultrahigh temperature alloys with B and Hf additions

Four Nb–Si based ultrahigh temperature alloys with compositions of Nb-22Ti-16Si-5Cr-3Al-mHf-nB ((m, n) = (0, 0), (0, 2), (4, 0) and (4, 2), respectively) (at.%) were prepared by vacuum non-consumable arc melting and then heat-treated at 1450 °C for 50 h. The effects of B and Hf additions on the phase selection, phase stability, microstructure and microhardness of these alloys under both as-cast and heat-treated conditions have been investigated. The results show that the microstructures of all the four alloys are composed of primary silicide blocks, Nbss dendrites together with one or two types of eutectic colonies around. However, the crystal structures of silicides, types of eutectic and amounts of constituent phases have obviously varied with B or Hf addition. Moreover, a low melting point three-phase eutectic is also observed in Hf-containing alloys. After 1450 °C/50 h heat-treatment, the microstructural uniformity of the alloys has been significantly ameliorated as well as their equilibrium phases have been basically obtained, and also some phase transformation reactions have occurred. The microhardness of the constituent phases present in the alloys is dependent on their types or crystal structures.     

Synthesis and Structural Determination of Nine-coordinate K_2[Y~Ⅲ(dtpa)(H_2O)]·7H_2O

1 ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｃｏｍｐｏｕｎｄｓｏｆｔｈｅｒａｄｉｏａｃｔｉｖｅｅｌｅ ｍｅｎｔ90 Ｙｈａｖｅｏｆｔｅｎｂｅｅｎｕｓｅｄｆｏｒｔｈｅｔｒｅａｔ ｍｅｎｔｏｆｅｖｅｒｙｋｉｎｄｏｆｃａｎｃｅｒ[1]ｂｅｃａｕｓｅｔｈｅｙｃａｎｅｍｉｔｐｕｒｅａｎｄｈｉｇｈ ｅｎｅｒｇｙ β ｒａｙａｎｄｐｏｓｓｅｓｓｔｈｅａｐｐｒｏｐｒｉａｔｅｈａｌｆ ｌｉｆｅ (ｔ1/ 2 =64 0ｈ)ａｎｄｍｏｄｅｒａｔｅｅｎｅｒｇｙ(Ｅｍａｘ=2 .2 7ＭｅＶ) .Ｈｏｗｅｖｅｒ,ｔｈｅｒａｄｉｏａｃｔｉｖｅｒａｙｓｏｆｔｈｅ90 Ｙｉ…     

A crystallographic re-investigation of Cu2Sb-related binary,ternary, and quaternary structures: how many structure types can exist upon the same topology of a unit cell?

Crystal chemical analysis of several large sets of topologically related structures confirms earlier suggestions that within the same cell content, space group, and Wyckoff site occupancies, there may exist several structure types of sometimes quite different coordination chemistry and bonding arrangement. The original Flahaut's suggestion of demarcating anti-Cu₂Sb and PbFCl structure types has been extended to an analysis of structures of over 350 compounds in terms of various structural characteristics as free parameters. For the Cu₂Sb family, structural field maps indicate formation of at least three distinct structure types: Cu₂Sb, PbFCl, CeFeSi (anti-type of PbFCl) and UAs₂ (which is not an anti-type of Cu₂Sb). The formerly suggested ternary ZrSiS structure type is in fact an ordered version of UAs₂. Extension of this approach to “filled” versions of these structure types permits clear demarcation of two other topologically related structure types, LaOAgS and HfCuSi₂, the latter being a derivative of UAs₂ but not Cu₂Sb. Very similar relationships have been observed for several smaller structural families. Perspectives of using different structural parameters as free coordinates are discussed.     

CRYSTAL STRUCTURE AND MICROSTRUCTURE OF RAPIDLY SOLIDIFIED La(Ni, Sn)（5+x）(x=0.1---0.4) HYDROGEN STORAGE ALLOYS

采用常规熔铸和单辊快凝制备了CaCu5型贮氢合金La(Ni,Sn)5 x(x=0．1—0．4),用X射线衍射及扫描电镜分析了合金显微形貌、纳米晶粒和晶体结构的特征及相互间关系．XRD Rietveld分析表明,常规熔铸方法制备的La-Ni-Sn三元合金含有数量较多的沿C轴定向排列的Ni-Ni“哑铃”对,其纳米级晶粒呈扁平状,电镜观察显示该合金具有粗大的树枝状形貌,除La-Ni-Sn三元合金外,在熔铸合金中尚有一定量的LaNi5合金和单质Sn存在．单辊快凝制备的合金随着冷凝速度的加快,合金的纳米级晶粒沿(001)晶面法线方向明显变长,但沿(100)晶面法线方向的尺寸长大较慢,在高快凝速率下(10,15,20m／s),合金的显微形貌由细小的柱状与等轴状晶块组合而成．     

Magnetic Properties and Nanocrystalline Phases in Sn Containing SmCo5 Alloys

SmCo₅ alloys with Sn additions (0.2-2.0 at.%) were prepared by mechanical milling of arc-melted samples. The nano-phase structures and magnetic properties of as-milled powders were investigated. The Sn additions resulted in development of nanocrystalline structures producing exchange-coupled magnets with better remanence magnetization to maximum magnetization ratios (M _r/M _max), typically 0.92 at 9.9 kOe coercivity. In addition, it was observed that the Sn concentrations lead to higher M _r/M _max ratios and maximum magnetization accompanying lower coercivity. X-ray diffraction revealed formation of 2:17 and 2:7 phases in 1:5 matrix, which were found to be dependent on Sn percentage. It appeared that higher Sn concentrations promoted 2:17 phase and helped in the formation of nano-sized phases.     

Crystal structure of La5Ti4GaO17

The crystal structure of La₅Ti₄GaO₁₇ compound synthesized by heat-treatment of the co-precipitated hydroxy-oxalates has been determined by the X-ray powder diffraction. It was found that crystal structure of La₅Ti₄GaO₁₇ belongs to the CaLa₄Ti₅O₁₇-type structure (space group Pmnn, a = 0.3912(1) nm, b = 3.128(1) nm, c = 0.5523(1) nm, Z = 2). The final R_W value is equal to 0.081 for 169 independent reflections.     

The ytterbium-copper-aluminium system

The isothermal section of the Yb---Cu---Al phase diagram at 870 K over the whole concentration region has been constructed using X-ray structure and phase analysis. We have confirmed the existence of earlier reported ternary compounds: YbCuAl (ZrNiAl type) and YbCu₄Al₈ (CeMn₄Al₈ type); the previously reported compound YbCu₄Al proved to be a solid solution of aluminium in the binary compound YbCu₅ (CaCu₅). New ternary aluminides such as Yb₄(Cu_0.26Al_0.74)₃₃ (new structure type), Yb₂(Cu_0.57Al_0.43)₁₇ (Th₂Zn₁₇), Yb(Cu_0.85Al_0.15)₆ (YbMo₂Al₄)₇ Yb₆(Cu_0.74Al_0.26)₂₃ (Th₆Mh₂₃) and Yb(Cu_0.30Al_0.70)₃ (PuNi₃) have been prepared for the first time and their crystal structures have been determined. The limits of solid solutions of the binary compound YbCu₅ and the homogeneity ranges of the ternary phases Yb(CuAl)₁₂, Yb(CuAl)₁₇ and Yb(CuAl)₂ have been established.     

Synthesis improvement,crystal structure and a charge-transfer complex of a sulphur dioxide-containing TTF derivative

An improvement in the synthesis of donor 2 that permits to have a better yield and to avoid the manipulation of H₂S has been carried out. Crystals suitable for X-ray structure determination have been obtained and in the crystal structure short hydrogen bonding interactions forming pairs of chains are observed. A charge-transfer complex 2:TCNQ 4:5 has also been prepared and characterised showing high room temperature conductivity.