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91.
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Dirk JohrendtGunter Kotzyba Henning TrillBernd D. Mosel Hellmut EckertThomas Fickenscher Rainer Pöttgen† 《Journal of solid state chemistry》2002,164(2):201-209
Single-phase samples of REAgMg (RE=La, Ce, Eu, Yb) and EuAuMg were prepared by reacting the elements in sealed tantalum tubes in a high-frequency furnace. LaAgMg and CeAgMg adopt the hexagonal ZrNiAl-type structure, while EuAgMg, YbAgMg, and EuAuMg crystallize with the orthorhombic TiNiSi type. Chemical bonding was exemplarily investigatedfor EuAgMg and EuAuMg on the basis of TB-LMTO-ASAcalculations. Magnetic susceptibility measurements indicatePauli paramagnetism for LaAgMg and YbAgMg with room-temperature susceptibilities of 2.4(1)×10−9 and 1.5(1)×10−9 m3/mol, respectively. CeAgMg remains paramagnetic down to 2 K. The experimental magnetic moment of 2.52(2) μB/Ce above 50 K is compatible with trivalent cerium. EuAgMg and EuAuMg are paramagnetic above 50 K with experimentalmagnetic moments of 7.99(5) μB/Eu for the silver and 7.80(5) μB/Eu for the gold compound, indicating divalent europium. Ferromagnetic ordering is detected at TC=22.0(3) K (EuAgMg) and TC=36.5(5) K (EuAuMg). At 4.2 K and 5 T the saturation magnetizations are 7.1(1) and 7.3(1) μB/Eu for EuAgMg and EuAuMg, respectively. According to the very small hysteresis, EuAgMg and EuAuMg may be classified as soft ferromagnets. All compounds are metallic conductors. For EuAgMg and EuAuMg freezing of spin-disorder scattering is observed below TC. At 78 K 151Eu Mössbauer spectra show isomer shifts of −9.00(4) and −8.72(8) mm/s for EuAgMg and EuAuMg, respectively. Full magnetic hyperfine field splitting is detected at 4.2 K with hyperfine fields of 17.4(1) and 18.3(2) T at the europium nuclei of EuAgMg and EuAuMg. 相似文献
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Eu5Ge3 and EuIrGe2 were prepared from the elements in tantalum tubes, and their crystal structures were determined from single crystal X-ray data. Eu5Ge3 adopts the structure of Cr5B3: I4/mcm, a = 799.0(1)pm, c = 1 536.7(1)pm, Z = 4, wR2 = 0.0421 for 669 F2 values and 16 variables. The structure of Eu5Ge3 contains isolated germanium atoms and germanium atom pairs with a Ge? Ge distance of 256.0 pm. Eu5Ge3 may be described as a Zintl phase with the formulation [5 Eu2+]10+[Ge]4?[Ge2]6?. Magnetic investigations of Eu5Ge3 show Curie-Weiss behaviour above 50 K with a magnetic moment of μexp = 7.6(1) μB which is close to the free ion value of μeff = 7.94 μB for Eu2+. EuIrGe2 is isotypic with CeNiSi2: Cmcm, a = 445.5(2) pm, b = 1 737.4(4) pm, c = 426.6(1) pm, Z = 4, wR2 = 0.0507 for 295 F2 values and 18 variables. The structure of EuIrGe2 is an intergrowth of ThCr2Si2-like slabs with composition EuIr2Ge2 and AlB2-like slabs with composition EuGe2 in an AB stacking sequence. Both slabs are distorted when compared to the symmetry of the prototypes. The Ge? Ge distance of 256.6 pm in the AlB2-like fragment is comparable to that in Eu5Ge3. 相似文献
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Three fractions of SiC platelets were characterized using polarizing microscopy, X-ray diffraction, high resolution Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA) and scanning electron microscopy with energy dispersive analysis (SEM/EDX). The chemical analysis of the three fractions is given. The determination of the SiC polytypes (4H, 6H, 15R, 3C) was done and has been correlated with the chemical analysis. The results of the X-ray diffraction investigations confirm the polarizing microscopy observations. Using microanalytical techniques important conclusions about the impurity elements (e.g. B, Al, Fe) and their local distribution could be drawn. Most of them were found to be present on the outermost surfaces of the platelets. Some conclusions concerning the processing of the platelets are suggested.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday 相似文献
98.
Four new stationary phases for HPLC were prepared by modifying silica gel with a trifrnctional aminoalkyl silane. A conjugated π-electron system was linked to the amino group either directly or with a carboxylic anhydride as a spacer in between. Characterization and dynamic measurements of the new stationary phases were performed by solid state NMR spectroscopy. The results of the 29si and 13C CP/MAS techniques were compared with the recently developed 1H MAS-only technique. Despite strong homonuclear dipole-dipole interactions it was possible to obtain well resolved 1H MAS spectra of those stationaru phases with a high degree of crosslinking. Limited mobility of the aromatic ligand fragments is common for all examined stationaryu phases. The chromatographic properties of the new phases were tested by their ability tio sepatate a mixture of eight PAHS. It could be shown that the π-π interaction mechanism is responsible for the separation of the eight PAHs, because the elution order of the PAHs did not changem despite the use of both a nonpolar mobile phase (n-heptane) and a polar mobile phase (methanol/ water mixture). 相似文献
99.
The cyclization of (2-ethynylphenyl)triazenes in ODCB at 200 degrees C gives exclusively cinnolines, whereas addition of CuCl to 1,2-dichloroethane solutions of the triazenes at 50 degrees C results in the sole formation of isoindazoles. DFT calculations and deuterium labeling studies suggest the intermediacy of a 3-dehydrocinnolinium ion, produced through a pericyclic transition state. Calculations and trapping studies strongly implicate a carbene intermediate in isoindazole formation, which proceeds through a pseudocoarctate transition state. 相似文献
100.
On Ternary Thallium Chalcogenides with Thallium Selenide Structure. By means of single crystal investigations, it has been confirmed that the compounds TlGaTe2, TIInSe2, and TIInTe2 crystallize in the TISe type (B37). As an univalent cation thallium is surrounded by eight chalcogen atoms. Gallium and indium are trivalent with tetrahedral coordination and covalent bonds. The interatomic distances as well as coordination and bonding resulting from them are discussed. 相似文献