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61.
Lawes G Harris AB Kimura T Rogado N Cava RJ Aharony A Entin-Wohlman O Yildirim T Kenzelmann M Broholm C Ramirez AP 《Physical review letters》2005,95(8):087205
We show that long-range ferroelectric and incommensurate magnetic order appear simultaneously in a single phase transition in Ni3V2O8. The temperature and magnetic-field dependence of the spontaneous polarization show a strong coupling between magnetic and ferroelectric orders. We determine the magnetic symmetry using Landau theory for continuous phase transitions, which shows that the spin structure alone can break spatial inversion symmetry leading to ferroelectric order. This phenomenological theory explains our experimental observation that the spontaneous polarization is restricted to lie along the crystal b axis and predicts that the magnitude should be proportional to a magnetic order parameter. 相似文献
62.
U.?Pal J.F.?Sanchez Ramirez H.B.?Liu A.?Medina J.A.?AscencioEmail author 《Applied Physics A: Materials Science & Processing》2004,79(1):79-84
The synthesis of bimetallic nanoparticles has become so important in recent times due to its multi-faceted applications. The structure of the synthesised particles influences directly their properties. In this paper, we report the synthesis of Au/Cu nanoparticles by a simultaneous reduction method, considering three different molar concentrations (AuCu, AuCu3 and Au3Cu) of the components. In order to determine the size and structure of the obtained clusters, the particles were examined by optical spectroscopy, transmission electron microscopy and high-resolution transmission electron microscopy. One of the major factors, the minimum bimetal formation energy, was calculated by an embedded-atom method. The relation between the Au/Cu proportions has been demonstrated to affect the size of the particles and the corresponding structures. From the basic structural analysis it is found that the particles were fcc-like, multiple twin or multiple defect particles for the different Au/Cu concentrations. The smallest particles were identified for the Au/Cu sample with 50% of each, and the most crystalline structures were also obtained in the same sample. PACS 61.46.+w; 61.16.-d; 31.15.Qg 相似文献
63.
E. I. Klimova E. A. Vazquez Lopez T. Klimova M. Martinez Garcia Ortega S. Hernandez L. Ruiz Ramirez 《Russian Journal of General Chemistry》2004,74(11):1757-1762
Ferrocenyltetrahydropyrimidin-2-ones were prepared by reactions of linear and cyclic ,-unsaturated ketones of the ferrocene series with urea in i-PrOH in the presence of t-BuOK. The structures of the compounds prepared were studied by 1H and 13C NMR and IR spectroscopy, and also by single crystal X-ray diffraction.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1887–1893.Original Russian Text Copyright © 2004 by E. Klimova, Lorez, T. Klimova, Garcia, Hernandez, Ramirez.This revised version was published online in April 2005 with a corrected cover date. 相似文献
64.
Using a simple model it is shown that the cost of constraining a hydrated potassium ion inside a narrow nanopore is smaller than the cost of constraining the smaller hydrated sodium ion. The former allows for a greater distortion of its hydration shell and can therefore maintain a better coordination. We propose that in this way the larger ion can go through narrow pores more easily. This is relevant to the molecular basis of ion selective nanopores and since this mechanism does not depend on the molecular details of the pore, it could also operate in all sorts of nanotubes, from biological to synthetic. 相似文献
65.
66.
We have measured the specific heat C(T) of the S = 3 / 2 Kagome-lattice-containing compound SrCr (9p)Ga (12-9p)O (19). We find little field dependence of the low-temperature C(T), consistent with a low-energy spectrum dominated by many-body singlet excitations. At high temperatures, we recover only approximately 50% of the total R ln4 entropy. 相似文献
67.
Mauricio Gomes Constantino Valquiria Aragão Gil Valdo José da Silva 《Tetrahedron letters》2008,49(8):1393-1395
The core structure of the natural sesquiterpene lactones furanoheliangolides, an 11-oxabicyclo[6.2.1]undecane system, was synthesized through a pathway involving two Diels-Alder reactions. 相似文献
68.
Karla Calfumán María Jesus Aguirre Diego Villagra Claudia Yañez Carmen Arévalo Betty Matsuhiro Leonora Mendoza Mauricio Isaacs 《Journal of Solid State Electrochemistry》2010,14(6):1065-1072
In this work, the modification of a glassy carbon electrode with tetraruthenated porphyrins electrostatically assembled onto
a Nafion film, previously adsorbed on the electrode surface, is reported. This modified electrode was characterized by scanning
electron microscopy–energy-dispersive X-ray, Raman spectroscopy, UV-Vis spectroelectrochemistry, and cyclic voltammetry. The
Nafion film onto the glassy carbon electrode shows a smooth disposition; when the tetraruthenated porphyrin is incorporated
on the Nafion film, the complex is adsorbed in a homogeneous way. The modified electrode catalyzes HSO3− oxidation in water–ethanol solutions and shows an enhanced stability compared with the electrode modified with the dip coating
method. Rotating disk electrode experiments showed a kinetic limitation to the electron transfer controlled by charge propagation
in the film. I/E curves show a Tafel slope of 120 mV/decade corresponding to a first electron-transfer reaction, depending on the potential,
as the determining step. Spectroelectrochemical experiments demonstrated that Ru(II) is the active site for the electrocatalysis. 相似文献
69.
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