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161.
A. Schleicher 《Fresenius' Journal of Analytical Chemistry》1954,143(2):132
Ohne Zusammenfassung 相似文献
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A. Kurtenacker A. Schleicher und Th. Breyhan 《Fresenius' Journal of Analytical Chemistry》1955,145(5):355-357
Ohne Zusammenfassung 相似文献
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K. Cruse G. Denk A. Schleicher und H. Sperlich 《Fresenius' Journal of Analytical Chemistry》1955,145(4):286-288
Ohne Zusammenfassung 相似文献
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Mössbauer studies of 57Fe in RFe2 (R = Y, Tb, Dy, Ho) at temperatures 300 to 800 K and in R(Co0.98Fe0.02)2 (R = Tb, Dy) at temperatures 85 to 300 K have been performed. The spectra yield the temperature dependence of the easy axis of magnetization, the magnetic hyperfine fields, electric field gradients and isomer shift. From the total Mössbauer absorption area the recoil free fraction was determined. The relative intensities of the various Mössbauer absorption lines yield the anisotropy in the recoil free fraction. In all compounds, except in YFe2, all measured quantities show large variations near the magnetic phase transition temperature (Tc). The variation in the recoil free fraction and in its anisotropy and the variation in the electric field gradient are all consistent, quantitatively, with anisotropic softening in the vibration modes of the Fe nucleus near Tc In RFe2 the modes in which the iron vibrates along the local C3h symmetry axes are softened less than the perpendicular modes. In RCo2 it is the other way around. It seems, that these critical softening phenomena are due to the strong magnon-phonon coupling present in these materials and absent in YFe2. This conclusion is confirmed by a theoretical analysis given in an adjacent paper. In it we use the Green function method to calculate the average of the square of vibrational amplitudes in a Debye solid with a strong magnon-phonon coupling at temperatures close to the magnetic phase transition. We show that these amplitudes may increase or decrease near Tc depending on the details of the coupled system. 相似文献
170.
Israel Goldberg Lon-Tang W. Lin Harold Hart 《Journal of inclusion phenomena and macrocyclic chemistry》1984,2(1-2):377-389
This paper reports crystalline complexes of the new hosts N,N'-ditritylurea (DTU) and N-tritylurea (NTU) with various uncharged molecular guests. The crystal structures of the following complexes were elucidated by single crystal X-ray diffraction analysis at 115oK: (I) 1:1 DTU-propanamide — space group C2/c, a=15.839Å, b=9.088Å, c=24.584Å, =111.05o, Z=4; (II) 1:1 DTU-ethyl N-acetylglycinate — space group P1, a=9.010Å, b=10.800Å, c=19.810 Å, =105.29o =94.33o, =93.03o, Z=2; (III) 2:1 NTU-N, N-dimethylformamide — space group Cc, a=29.614Å, b=8.906Å, c=16.127Å, =121.04o, Z=4. The three crystal structures are stabilized mainly by a cooperative effect of hydrogen bonding between amide fragments displaced along the shortest axis of each crystal. This interaction occurs between host and guest in complexes I and II, and between host and host in complex III. The latter also represents a cage-type clathrate in which the guest molecules are accommodated in voids between the hydrophobic fragments of four neighboring NTU hosts. On the other hand, complexes of DTU are characterized by a more specific interaction between the two components, each guest molecule being inserted between two adjacent hosts (related by translation) and strongly bound to them via hydrogen bridges. These results illustrate a useful concept in the design of molecular species which can be potential hosts upon crystallization with neutral molecular guests.
Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82022 (7 pages). 相似文献