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B. Schmid B. Dorner D. Visser M. Steiner 《Zeitschrift für Physik B Condensed Matter》1992,86(2):257-262
The magnetic excitations in CsFeBr3 have been measured with inelastic scattering of cold neutrons to high precision at 80 mK. The fact that the lowest frequency mode softens with decreasing temperature but stabilizes at 0.11 THz below 2.5 K is the indication that CsFeBr3 remains a SGS system forT0.From dispersion curves measured earlier in a magnetic field along the chain axis experimental intensities were derived and in turn correlation lengths. Correlation lengths were also calculated using the new parameters for exchange and anisotropy. The experimental results and the calculations both show that the correlation lengths increase for increasing magnetic field, flatten off around the phase transformation at 4.1 Tesla with a maximum of about 35 Å and then decrease again for higher fields. No critical phenomena connected with this phase transformation could be detected.The Mirror Mode published earlier was found to be of spurious origin due to double scattering. It does not exist. 相似文献
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Oxidefluorides of Niobium and Tantalum The reaction of NbF5 with SiO2 (silica glass ampules) at 310°C or with SiO2 (Aerosil) at 180°C always leads to NbO2F. To the contrary the reaction with laboratory glass (Jenaer Geräteglas) at 130°C leads to NbOF3. TaF5 reacts in silica glass ampules at 400°C by formation of TaO2F, however at 300°C or 260°C by formation of TaOF3. Silica glass did not react with NbF5 at 130°C, however Nb2O5 and NbF5 gave at 130°C in silica glass ampoules NbOF3. Similarly, TaF5 and Ta2O5 or TaO2F formed at 260°C in nickel ampoules TaOF3. The chemical and the thermochemical behaviour of oxidefluorides have been investigated. The compounds NbOF3 and TaOF3 are isomorphic. Lattice constants are mentioned. 相似文献
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Syntheses and Structures of Trilithium Cyclotriphosphazenates Equipped with 2‐Halo‐aryl Substituents
Hexakis (2‐halo‐anilino) cyclotriphosphazenes (2‐X‐C6H4NH)6P3N3 {X = F ( 1d ), Cl ( 1e ), Br ( 1f )} were prepared by refluxing mixtures of hexachloro cyclotriphosphazene, 2‐haloaniline and triethylamine in toluene and characterized by single crystal X‐ray diffraction. 1d , 1e and 1f were reacted with nBuLi in thf. Reactions were monitored with 31P NMR. Addition of three equivalents of nBuLi yields lithium complexes of trianionic phosphazenates [{(thf)2Li}3{(2‐X‐C6H4N)3(2‐X‐C6H4NH)3P3N3}] {X= F ( 2d ), Cl ( 2e ) and Br ( 2f )}. 2d , 2e and 2f were structurally characterized by X‐ray diffraction, which reveals monomeric cis‐metalated phosphazenates featuring central P3N3 ring systems of chair conformation. Lithium ions reside in three N(eq)‐P‐N(endo) chelation sites at one face of the P3N3 ring system. Li…X distances are rather long (> 3Å) indicating no Li‐X interactions. 相似文献
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Propylene was polymerized with the catalyst system (C2H5)2A1C1/ VCk/ anisole at -78°C using various conditions. The resulting polymers were successively extracted by diethyl ether, hexane, and heptane, leaving the residue. The polymers of the four series were characterized by intrinsic viscosity, gel permeation chromatography, 13C nuclear magnetic resonance, infrared spectroscopy, x-ray diffraction, and by differential scanning calorimetry. The combined evidence from the various methods indicates that this catalyst system leads to stereoblock polymers which can be fractionated according to stereochemical composition and sequence length. 相似文献
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The standard deviation [sgrave] is known to be an absolute measure of Gaussian (G) distributions, because it (or multiples of it) always determines a constant fraction of the material. However, this is not true for distribution functions other than Gaussian. The weight fractions corresponding to weight standard deviations (±[sgrave]w) of Schulz-Flory distributions depend on the polymolecularity index xw/xn, approaching a limiting value of W(xw ± [sgrave]w) = 86.5 for xw/xn →∞. The use of weight standard deviations is meaningless for generalized logarithmic normal (LN) distributions if xw/xn 52. The weight fractions W(Xn ± [sgrave]n) around the number-average degree of polymerization of G and LN distributions first go through a maximum before decreasing with increasing xw/xn. The weight fractions W(xn ± [sgrave]n) decrease steadily with higher xw/xn. 相似文献
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