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F. Ylli Y. Gros C. Meyer F. Hartmann-Boutron P. Strobel M. Novak J. L. Tholence 《Hyperfine Interactions》1994,93(1):1727-1731
Comparison of RT Mössbauer spectra of samples prepared with low
and high
suggests incomplete oxygenation of low
samples. At lowT, the magnetic hfs appears very gradually, without hf anomalies. 相似文献
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S. Zherlitsyn B. Lüthi V. Gusakov B. Wolf F. Ritter D. Wichert S. Barilo S. Shiryaev C. Escribe-Filippini J.L. Tholence 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):59-66
We report results of the ultrasonic investigation of Ba1-xKxBiO3 superconducting (SC) single crystals for two potassium concentrations and in a wide temperature range including the normal and the SC states. An instability of the crystal lattice that develops above
the superconducting phase transition leads to a softening of both the transverse c44 and the longitudinal c11 modes at temperatures between 200 K and 50 K. In the case of Ba0.65K0.35BiO3 a pronounced hysteresis was discovered. Low temperature X-ray powder diffraction analysis does not reveal any change of the
cubic structure in the samples within a resolution of our X-ray technique. The softening of the elastic moduli, the hysteresis,
the maximum in the attenuation of sound along with the possible short- (or long-) range structural distortion can be explained
qualitatively in a simple model by assuming a coupling of the acoustic modes with the anharmonic oscillations of BiO6 octahedra. Some weak anomalies are discovered in the velocity of the longitudinal sound in the vicinity of the superconducting
phase transition.
Received 25 June 1999 and Received in final form 14 February 2000 相似文献
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Carreno MC Garcia Ruano JL Urbano A Remor CZ Arroyo Y 《The Journal of organic chemistry》2000,65(2):453-458
Diels-Alder reactions of (SS)-2-(2'-methoxynaphthylsulfinyl)-1, 4-benzoquinone (1b), 2-(p-methoxyphenylsulfinyl)-1,4-benzoquinone (1c), and 2-(p-nitrophenylsulfinyl)-1,4-benzoquinone (1d) with cyclopentadiene are reported. These cycloadditions allowed the highly chemo- and stereoselective formation of both diastereoisomeric endo-adducts resulting from reaction on the unsubstituted double bond C(5)-C(6) of quinones working under thermal and Eu(fod)(3)- or BF(3).OEt(2)-catalyzed conditions. The synthesis of endo-adduct [4aS,5S,8R,8aR,SS]-9d resulting from cycloaddition on the substituted C(2)-C(3) double bond was achieved in a chemo- and diastereoselective way from quinone 1d in the presence of ZnBr(2). The reactivity and selectivity of the process proved to be dependent on the electron density of the arylsulfinyl group. 相似文献
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Garcia Ruano JL Barros D Maestro MC Slawin AM Page PC 《The Journal of organic chemistry》2000,65(19):6027-6034
The asymmetric aldol reaction of 1,2-diketones, masked as nonracemic 2-acyl dithiane oxides, with lithium enolates derived from several esters and lactones, proceeds with a high degree of stereocontrol at both carbonyl and enolate prochiral centers, the stereocontrol mainly determined by the configuration of the sulfoxide sulfur atom. The sense of induced stereochemistry observed for ester enolates is different from that seen for lactone enolates. Hydrolysis of the dithiane oxide units of the major diastereoisomerically pure aldol products affords enantiomerically pure tertiary alpha-substituted beta-hydroxy-gamma-ketoesters. 相似文献
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The transition paramagnet—spin glass is investigated in γ-Fe70Ni30-cMnc alloys using a.c.-susceptibility, Mössbauer effect and small angle neutron scattering measurements. Different behaviours are proposed depending on the Mn concentration. 相似文献