Chemical bond characteristics, thermal expansion property and compressibility of AR(2)O(4) (A = Ca, Sr, Ba; R = rare earths)

Theoretical researches were performed on the CaFe2O4-type binary rare earth oxides AR(2)O(4) (A = Ca, Sr, Ba; R = rare earths) by using chemical bond theory of dielectric description. The chemical bond properties of these crystals were explored, and then the thermal expansion property and compressibility were studied. The theoretical values of linear thermal expansion coefficient (LTEC) and bulk modulus were presented. The calculations revealed that the LTECs and the bulk moduli do have linear relationship with the ionic radii of the rare earths. In the cases of Sc and Y, both the LTEC and bulk modulus values are larger than the lanthanide series. We attribute this to the difference in the electronic configuration between Sc (Y) and lanthanide series. For SrY2O4 and BaY2O4 crystals, the theoretical values of LTEC and bulk modulus agree well with experimental ones.

Reduction of Eu3+ to Eu2+ in MAl2Si2O8 (M = Ca, Sr, Ba) in air condition

In general, the reduction of Eu3+ to Eu2+ in solids needs an annealing Process in a reducing atmosphere. in this paper, it is of great interest and importance to find that the reduction of Eu3+ to Eu2+ can be realized in a series of alkaline-earth metal aluminum silicates MAl2Si2O8 (M = Ca, Sr, Ba) just in air condition. The Eu2+-doped MAl2Si2O8 (M = Ca, Sr, Ba) powder samples were prepared in air atmosphere by Pechini-type sol-gel process. It was found that the strong hand emissions of 4f(6)5d(1)-4f(7) from Eu2+ were observed at 417, 404 and 373 nm in air-annealed CaAl2Si2O8, SrAl2Si2O8 and BaAl2Si2O8, respectively, under ultraviolet excitation although the Eu3+ precursors were employed. In addition, under low-voltage electron beam excitation, Eu2+-doped MAl2Si2O8 also shows strong blue or ultraviolet emission corresponding to 4f(6)5d(1)-4f(7) transition.

Preparation and luminescent properties of rare earth ions in M2B5O9Cl : Re(M = Ca, Sr, Ba; Re=Eu, Tb)

M2B5O9X: Re(M = Ca, Sr, Ba; X = Cl, Br; Re = Eu, Th) phosphors were synthesized via solid state method. The products were characterized with X-ray powder diffraction and luminescence spectrometer. The luminescent properties as well. as the influences of the matrix composition and other doping ions on the luminescence of the rare earth ions of the co-doped phosphors were investigated. The coexistence of Eu3+, Eu2+ and Th3+ were observed in these matrices. The phenomenon may be explained by the electron transfer theory. The sensitization of Ce3+ ion improves the intensity of emission of Eu2+, and Tb3+. The competition between electron transfer among conjugate rare earth ions and energy migration might be the reasons for the observation. We predict a novel trichromatic phosphor co-doped with Eu3+ Tb3+ in M2B5O9X.

Structural analysis of PEKEKK(T/I) using WAXD, imaging plates and SAXS

Structures and crystal form transition of the novel aryl ether ketone polymer containing meta-phenylene linkage: PEKEKK(T/I) were investigated by wide angle X-ray diffraction (WAXD), imaging plates (IPs) and small angle X-ray scattering (SAXS). The energy of activation of the decomposition reaction and degree of crystallinity of PEKEKK(T/I) were determined by WAXD and thermo-gravimetric analysis (TGA), respectively. Results obtained from WAXD and IPs show that crystal forms I and II coexist in the PEKEKK(T/I) samples isothermally cold crystallized in the temperature range from 180degreesC to 240degreesC and only form I occurs in PEKEKK(T/I) samples isothermally cold crystallized at 270degreesC. The radius of gyration (Rg), thickness of microregions with electron-density fluctuations (E) and distribution of particle sizes were investigated by SAXS.

Effect of Ce and MgO on NO decomposition over La1-x-Ce-x-Sr-Ni-O/MgO

Ce and MgO were added simultaneously to La-Sr-Ni-O catalyst and a substantial enhancement of activity for NO decomposition was observed, which may be attributed to the formation of a new highly active site caused by the addition of Ce and MgO.

Synthesis, characterization and crystal structure of a new layered heterometallic coordination polymer {[(CuL) Sr-2(H2O)center dot Sr-2(H2O)(7)]center dot 2H(2)O center dot 0.5CH(3)OH}(n)

A copper-strontium heterometallic coordination polymer was synthesized and characterized by elemental analysis and IR spectra. The crystal structure was determined by single-crystal X-ray diffraction analyses. The title complex is a 2 D coordination polymer with the chemical formula [[(CuL)(2)Sr (H2O) center dot Sr-2 ((HO)-O-2)(7)]center dot 2H(2)O center dot 0.5CH(3)OH](n), where H4L = N-(2-hydroxybenzamido)-N'-(3-carboxylsalicylidene) ethylenediamine. Its structural unit is comprised of two adjacent units, which polymerized with each other to form a new layered heterometallic coordination polymer.

Chemical bond properties and Mossbauer spectroscopy in (La1-xMx)(2)CuO4(M=Ba, Sr)

By using the average band-gap model, the chemical bond properties of (La1-x, M-x)(2)CuO4(M=Ba, Sr) were calculated. The calculated covalencies for Cu-O and La-O bond in the compounds are 0.3 and 0.03 respectively. Mossbauer isomer shifts of Fe-57 doped in La2CuO4 and Sn-119 doped in La2CuO4 were calculated by using the chemical surrounding factor defined by covalency and electronic polarizability. Four valence state tin and three valence iron sites were identified in Fe-57 and Sn-119 doped La2CuO4.

Microstructure analysis of nylon 66 by WAXD and SAXS

The analysis of the small angle X-ray scattering (SAXS) data was based upon particle characteristic function, one-dimensional electron-density correlation function and particle distribution function. The microstructure of nylon 66 with different degrees of crystallinity was studied by means of X-ray scattering method. The radius of gyration R-g, the Porod radius R-p, the thickness of crystalline region L-c the thickness of non-crystalline region L-n, the thickness of interphase region d(tr), the long period L, the semiaxises of particles (a, a, b), the distribution of the particle sizes and the scattering invariant were calculated. The results indicate that there was a significant interphase region between the crystalline region and the non-crystalline region. and its content (W-t,W-x) should not be neglected in comparison with that of crystalline region W-c,W-x. The morphology of nylon 66 prepared by isothermal crystallization at a high temperature was mainly a lamellar structure, while the spherical crystals dominated in the quenched sample. The size of the particles in the quenched sample was smaller than that of those in the isothermally crystallized sample. and the distribution of the particle sizes in the isothermally crystallized sample was wider.

M_2CeO_4(M=Ca,Sr,Ba)的结构与发光特性

Sr_2CeO_4是一种新型的一维结构发光材料,其特殊的结构对其发光特性有决定性的作用。Sr2CeO4体系中可以顺利地进行能量传递,产生较强电荷迁移发光。合成了M2CeO4（M=Ca,Sr,Ba）,发现与Sr2CeO4具有类似结构的Ba2CeO4也可以发光,而结构完全发生了变化的Ca2CeO4则不发光。

The role of redox property of La2-x(Sr,Th)(x)CuO4 +/-lambda playing in the reaction of NO decomposition and NO reduction by CO

Two systems of mixed oxides, La2-xSrxCuO4 +/- lambda (0.0 less than or equal to x less than or equal to 1.0) and La(2-x)Tn(x)CuO(4 +/-) (lambda) (0.0 less than or equal to x less than or equal to 0.4), with K2NiF4 structure were prepared. The average valence of Cu ions and oxygen nonstoichiometry (lambda) were determined by means of chemical analysis. Meanwhile, the adsorption and activation of nitrogen monoxide (NO) and the mixture of NO + CO over the mixed oxide catalysts were studied by means of mass spectrometry temperature-programmed desorption (MS-TPD). The catalytic behaviors in the reactions of direct decomposition of NO and its reduction by CO were investigated, and were discussed in relation with average valence of Cu ions, A and the activation and adsorption of reactant molecules. It has been proposed that both reactions proceed by the redox mechanism, in which the oxygen vacancies and the lower-valent Cu ions play important roles in the individual step of the redox cycle. Oxygen vacancy is more significant for NO decomposition than for NO + CO reaction. For the NO + CO reaction, the stronger implication of the lower-valent Cu ions or oxygen vacancy depends on reaction temperature and the catalytic systems (Sr- or Th-substituted). (C) 2000 Elsevier Science B.V. All rights reserved.

Eu~(2+):MAl_2O_4(M=Ba~(2+),Sr~(2+))的发光与晶体化学键相关性的研究

本文应用复杂晶体化学键理论对Eu~(2+):MAl_2O_4(M=Ba~(2+),Sr~(2+))晶体的化学键参数进行了计算,讨论了晶体中Eu~(2+)的发光性与其所取代离子格位的化学键性质间的关系。

M_2B_5O_9Cl:Eu(M=Ca,Sr,Ba)的真空紫外光谱特性的研究

采用高温固相反应法合成了M_2B_5O_9Cl:Eu(M=Ca,Sr,Ba)中荧光体,测量了荧光体的真空紫外激发光谱,研究了M_2B_5O_9Cl:Eu(M=Ca,Sr,Ba)的真空紫外光谱特性,观察到基质吸收带位于120～200 nm区域,Eu~(2+)离子的5d能级劈裂随着M~(2+)的半径的增加而减小,同时也观察到基质与稀土离子之间存在的能量传递。