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Titanates de cuivre substitués à structure bixbyite: Les composés Cu1−xTi1−xFe2xO3 (0.15 ≤ x ≤ 0.33)
A new bixbyite family, Cu1?xTi1?xFe2xO3 (0.15 ≤ x ≤ 0.33) has been synthesized and characterized. The unit cell is cubic: a ~ 9.40Å. The X-ray powder diffraction study shows up an isotypism with the (Fe, Mn)2O3 compounds. There is a disordered distribution of CuII, TiIV, and FeIII over the two cyrstallographic sites: PI and PII. PII is highly distorted (two long MO distances) by the Jahn-Teller effect of CuII. The bixbyite structure is described in terms of polyhedra arrangement, as a particular case of the CM2O3 family. The cation packing is discussed in relation with the existence of the bixbyite structure for the Cu1?xTi1?xFe2xO3 compounds. The electrical properties (σ ~ 10?5(Ω cm)?1 for x = 0.286 at room temperature) show an electron conduction with probably a hopping mechanism. 相似文献
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The preparation of a single phase LaNiO2 by controlled H2 reduction of the perovskite LaNiO3 is reported. The different steps of the synthesis are detailed. The structural characterization is made by X-ray diffraction (XRD) and neutron powder diffraction (NPD) and discussed; the derived crystal structure is the infinite-layer CaCuO2. Both XRD and NPD patterns are characterized by anisotropic shape broadening originating from size effect linked to the reduction process. From NPD, the LaNiO2 powder is composed of platelet-like crystallites having an average thickness equal to 20 nm along the [001] direction. A modulation of the neutron diffraction background is observed and discussed in connection to the reduction process. 相似文献
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D. De Barros L. Ortega Ch. Peroz F. Weiss P. Odier 《Physica C: Superconductivity and its Applications》2006,440(1-2):45-51
The synthesis of HgBCCO films by spray pyrolysis on single crystals is investigated. It is shown that in conditions where the precursor is expected to give Hg-1223, Hg-1212 grows on LaAlO3 (0 0 1) while Hg-1223 grows on MgO (0 0 1). The samples are analysed by X-ray pole figures, SEM and critical current measurements. Both samples were superconducting but the sample on MgO had a negligible Ic while 17 A was measured on LAO at 77 K (sf). These differences are analysed in terms of texture and microstructure and some conclusions concerning the growth are drawn. On LAO, the nucleation is probably epitaxial and the anisotropy of the growth inhibits the transformation into Hg-1223 while some interfacial contribution expected to occur on MgO makes this transformation easier. 相似文献
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Gallet B Aumaître S Boisson J Daviaud F Dubrulle B Bonnefoy N Bourgoin M Odier P Pinton JF Plihon N Verhille G Fauve S Pétrélis F 《Physical review letters》2012,108(14):144501
We report the first experimental observation of a spatially localized dynamo magnetic field, a common feature of astrophysical dynamos and convective dynamo simulations. When the two propellers of the von Kármán sodium experiment are driven at frequencies that differ by 15%, the mean magnetic field's energy measured close to the slower disk is nearly 10 times larger than the one close to the faster one. This strong localization of the magnetic field when a symmetry of the forcing is broken is in good agreement with a prediction based on the interaction between a dipolar and a quadrupolar magnetic mode. 相似文献
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Monchaux R Berhanu M Bourgoin M Moulin M Odier P Pinton JF Volk R Fauve S Mordant N Pétrélis F Chiffaudel A Daviaud F Dubrulle B Gasquet C Marié L Ravelet F 《Physical review letters》2007,98(4):044502
We report the observation of dynamo action in the von Kármán sodium experiment, i.e., the generation of a magnetic field by a strongly turbulent swirling flow of liquid sodium. Both mean and fluctuating parts of the field are studied. The dynamo threshold corresponds to a magnetic Reynolds number R(m) approximately 30. A mean magnetic field of the order of 40 G is observed 30% above threshold at the flow lateral boundary. The rms fluctuations are larger than the corresponding mean value for two of the components. The scaling of the mean square magnetic field is compared to a prediction previously made for high Reynolds number flows. 相似文献
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P. Odier J.-F. Pinton S. Fauve 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):373-378
We investigate experimentally the advection of a magnetic field by a flow of conducting fluid, at moderate magnetic Reynolds
numbers. More specifically, we study the influence of a large scale intense vortex on an externally applied field. We show
that at large scales the magnetic field lines are distorted in a way that is consistent with a scenario of magnetic field
expulsion by vorticity. Measurements at small scales show that the magnetic fluctuations are also quite sensitive to the large
scale vortex motion.
Received 27 October 1999 and Received in final form 16 March 2000 相似文献
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Thin films of mercury based superconductors were prepared on the R-plane sapphire with a CeO2 buffer layer using a two step process involving the deposition of the Hg-free precursor and ex situ mercuration in the sealed quartz tube. For the thin film preparation, a method with no contact between the mercury source
and the precursor film was used for mercuration. We studied the influence of the basic parameters of the mercuration (annealing
time, temperature and partial pressure of the mercury) regarding the composition and superconducting properties of prepared
Hg-based films to determine appropriate conditions for this mercuration method. We found out that an increased partial pressure
of mercury inhibited the creation of the parasitic Re-based phase and supported the crystallization of the superconducting
phase. The advantage of this mercuration method is higher reproducibility as well as its capability to prepare high quality
thin large areas films.
Presented at 5-th International Conference Solid State Surfaces and Interfaces, November 19–24, 2006, Smolenice Castle, Slovakia 相似文献