Structure of YAG crystals doped/substituted with erbium and ytterbium

Two series of yttrium aluminum garnets doped with erbium and ytterbium ions have been studied by single-crystal X-ray diffraction. The single crystals were obtained by the Czochralski method. The concentration of doping ions was established by the plasma emission spectroscopy method. For the Er series, it is equal to 23.4, 46.7, 72.5, and 100%, whereas, for Yb-doped YAGs, it equals 26.5, 48.2, 75.9, and 100%. The results are supplemented by the data obtained for pure YAG. The X-ray data for all samples were collected at two temperatures: 295(2) and 102(2) K. Additionally, for YAGs doped with ca. 50% of doping ions, some more detailed temperature measurements were performed. Pure single crystals of ErAG and YbAG were also studied as a function of diffraction angles. Careful single-crystal measurements utilizing a CCD diffractometer revealed the unit cell parameters, which slightly-but significantly-deviate from cubic symmetry. The average unit cell parameters change linearly with the amount of substituting Er and Yb cations, with two different slopes related to the ionic radii. Both of the dodecahedral distances depend linearly on the concentration of the substituting ions, but the longer dodecahedral distance also changes with temperature contrary to the shorter one. There is no correlation between the octahedral interatomic distance [Al(VI)...O] and the unit cell parameter or temperature; however, weak trends appear for the tetrahedral [Al(IV)...O] distance. Such weak trends are just the secondary consequences of the ion substitution taking place at the dodecahedral site. The dependences between the unit cell parameters and the concentration of doping ions allow us to establish concentrations of particular doping ions in mixed (Er, Yb) doped YAGs just on the basis of the measured unit cell parameters and knowledge of the amount of Y.     

含P—H键螺环五配位磷化合物的加成反应

5-氢-1,9-二氧-4,6-二氮-5-膦环-[4,4]壬烷1与二硫化碳、异硫氰酸酯反应,分别得到2-巯基二氢噻唑2和2-取代氨基二氢噻唑4,并用动态~(31)P NMR谱研究了其反应机理。     

Microanalytical Techniques Applied to Phase Identification and Measurement of Solute Redistribution at the Solid/Liquid Interface of Frozen Fe-4.3Ni Doublets

 A Fe-4.3Ni alloy has been solidified directionally by using the Bridgman system. The solidification conditions were chosen to obtain an oriented cellular structure of δ-ferrite. These are: a positive temperature gradient of about 60 K/cm and a growth rate of 6.6 μm/s. A change in these conditions can lead either to the formation of austenite or to the competitive growth of δ-ferrite/γ-austenite. The solid/liquid interface of δ-ferrite cells has been frozen and double instability has been revealed at the tip of the cells. The instability is described as the first harmonic wave of fundamental undulation, which appeared at the formerly planar solid/liquid interface. This means that a doublet structure is formed only with the imposed specific conditions of solidification. The Ni-solute redistribution after back-diffusion has been measured across the δ-ferrite doublet. Results of energy dispersive X-ray (EDX) measurements on the distribution of Ni and Fe correspond well to the theoretical prediction for redistribution developed especially for oriented structure formation (two dimensional solidification). Additionally, electron backscattered diffraction from the bulk Fe-4.3Ni alloy sample allowed us to determine the local structure, i.e. the distribution of single crystallite orientations in the microstructure. A unique correlation between fluctuations of the Ni-solute redistribution and crystalline orientations in the δ-ferrite doublets has been demonstrated. Moreover, a relationship between geometrical asymmetry of the doublets and solute redistribution has also been found.     

Round-off error analysis of iterations for large linear systems

Summary We deal with the rounding error analysis of successive approximation iterations for the solution of large linear systemsA _x =b. We prove that Jacobi, Richardson, Gauss-Seidel and SOR iterations arenumerically stable wheneverA=A ^*>0 andA has PropertyA. This means that the computed resultx _k approximates the exact solution with relative error of order A·A ^–1 where is the relative computer precision. However with the exception of Gauss-Seidel iteration the residual vector Ax _k –b is of order A² A ^–1 and hence the remaining three iterations arenot well-behaved.This work was partly done during the author's visit at Carnegie-Mellon University and it was supported in part by the Office of Naval Research under Contract N00014-76-C-0370; NR 044-422 and by the National Science Foundation under Grant MCS75-222-55     

5-氢-1,4,6,9-四氧-5-膦螺环[4.4]壬烷的制备及其硅烷基化反应

5-氢-1,4,6,9-四氧-5-膦螺环[4.4]壬烷2是合成有机磷阻燃剂的重要原料.其合成方法虽有一些报道,但尚未见2-氯-1,3,2-二氧膦杂环戊烷1与乙二醇反应的合成路线.我们用1、乙二醇及三乙胺以等摩尔比反应,发现2的收率很低,主要得到环状二亚磷酸酯3,将3再与乙二醇反应,很容易转化成2,反应式如下:     

2-(4′-氨基苯甲酰基)苯甲酸的合成方法改进

以邻苯二甲酸酐,乙酰苯胺为原料,二氯乙烷为溶剂,无水三氯化铝为催化剂,通过Friedel-Crafts酰基化反应制得2-(4′-乙酰氨基苯甲酰基)苯甲酸(1),1在酸性条件下回流,除去乙酰基得到2-(4′-氨基苯甲酰基)苯甲酸(2)。通过1H NMR,IR,MS和元素分析对1和2的结构进行了表征。最佳的Friedel-Crafts反应条件为:邻苯二甲酸酐20 mmol,n(邻苯二甲酸酐)∶n(乙酰苯胺)=1∶1,n(邻苯二甲酸酐)∶n(AlCl3)=1∶3,于45℃反应2 h,收率70.4%。     

A high‐order Godunov method for one‐dimensional convection‐diffusion‐reaction problems

In this article we develop a high‐order Godunov method for one‐dimensional convection‐diffusion‐reaction problems where convection dominates diffusion. The heart of this method comes from incorporating the diffusion term via the slope of the linear representation (recovery) of the solution on each grid cell. The method is conservative and explicit. Therefore, it is efficient in computing time. For constant coefficient linear convection, diffusion, and Lipschitz‐type reaction, the properties of the total variation stability and monotonicity preservation are proved. An error estimation is derived. Computational examples are presented and compared with the exact solutions. © 2000 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 16: 495–512, 2000     

Crystal and magnetic structure of a novel compound UCu5Al. Structural stability with Th-substitution

The antiferromagnetically ordered, moderate heavy fermion UCu₅Al, crystallises in the original tetragonal I4/mmm structure, which remains unchanged in the U_1−xTh_xCu₅Al solid solutions up to x≈0.35. Above this composition, other solid solutions with general chemical formula (U_1−xTh_x)(Cu_1−yAl_y)₅ are formed, having a different type of structure, namely the hexagonal CaCu₅-type. Below T_N=18 K UCu₅Al orders with a sine-modulated, incommensurate magnetic structure described by a wave vector k=(0, 0, 0.55) and the moment amplitude of 1.45(5) μ_B at 1.4 K.