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31.
Rana Saha A.K. Bera Y. Sundarayya S.M. Yusuf A. Sundaresan C.N.R Rao 《Journal of solid state chemistry》2011,184(3):494-9532
Magnetic properties of the Al1−xGaxFeO3 family of oxides crystallizing in a non-centrosymmetric space group have been investigated in detail along with structural aspects by employing X-ray and neutron diffraction, Mössbauer spectroscopy and other techniques. The study has revealed the occurrence of several interesting features related to unit cell parameters, site disorder and ionic size. Using first-principles density functional theory based calculations, we have attempted to understand how magnetic ordering and related properties in these oxides depend sensitively on disorder at the cation site. The origin and tendency of cations to disorder and the associated properties are traced to the local structure and ionic sizes. 相似文献
32.
33.
Prasant Kumar Nanda Manindranath Bera Ana Maria da Costa Ferreira Armando Paduan-Filho Debashis Ray 《Polyhedron》2009,28(18):4065-4071
The reaction of Cu(ClO4)2·6H2O with dimethylglyoxime (H2dmg) in a 1:1 mole ratio in aqueous methanol at room temperature affords the dinuclear complex [Cu2(μ-Hdmg)4] (1). Reaction of 1 with [Cu(bpy)(H2O)2](ClO4)2 (bpy = 2,2′-bipyridine) in a 1:1 mole ratio in aqueous methanol at room temperature yields the tetranuclear complex [Cu4(μ-Hdmg)2(μ-dmg)2(bpy)2(H2O)2](ClO4)2 (2). The direct reaction of Cu(ClO4)2·6H2O with H2dmg and bpy in a 2:2:1 mole ratio in aqueous methanol at room temperature also yields 2 quantitatively. The complexes 1 and 2 were structurally characterized by X-ray crystallography. Unlike the binding in Ni/Co-dmg, two different types of N?O bridging modes during the oxime based metallacycle formation and stacking of square planar units have been identified in these complexes. The neutral dinuclear complex 1 has CuN4O coordination spheres and complex 2 consists of a dicationic [Cu4(μ-Hdmg)2(μ-dmg)2(bpy)2(H2O)2]2+ unit and two uncoordinated ClO4? anions having CuN4O and CuN2O3 coordination spheres. The two copper(II) ions are at a distance of 3.846(8) Å in 1 for the trans out of plane link and at 3.419(10) and 3.684(10) Å in 2 for the trans out of plane and cis in plane arrangements, respectively. The average Cu–Noxime distances are 1.953 and 1.935 Å, respectively. The average basal and apical Cu?Ooxime distances are 1.945, 2.295 and 2.429 Å. The UV–Vis spectra of 2 is similar to the spectrum of the reaction mixture of 1 and [Cu(bpy)(H2O)2]2+. Variable temperature magnetic properties measurement shows that the interaction between the paramagnetic copper centers in complex 1 is antiferromagnetic in nature. The EPR spectra of frozen solution of the complexes at 77 K consist of axially symmetric fine-structure transitions (ΔMS = 1) and half-field signals (ΔMS = 2) at ca. 1600 G, suggesting the presence of appreciable Cu–Cu interactions. 相似文献
34.
New wormhole-like mesoporous TiO2 material has been synthesized through a convenient sol-gel method in the presence of a Schiff base secondary amine hexadecyl-2-pyrrole-methylamine (HPMA) containing chelating donor sites as template or structure directing agent (SDA). SDA molecules can be easily removed from the composite to generate mesoporosity and upon removal of the SDA molecule, this mesoporous TiO2 material showed very high surface area (480 ± 10 m2/g) with an average pore diameter of 2.57 ± 0.05 nm. When Rose Bengal dye is entrapped inside the nanopores of this material, it showed a drastic enhancement (ca. 40-folds) in the photoconductivity vis-à-vis mesoporous TiO2 alone under white light illumination. 相似文献
35.
Flake-built 3D β-In2S3 nanostructures were synthesized by thermolysis of S-methyl dithiocarbazate–indium(III) complex precursor in hexamethylenediamine (HMDA). XRD patterns showed that the cubic phase
of 3D β-In2S3 remained unchanged but the crystallinity was increased after annealing at 400 °C for 20 min. The products were also characterized
by SEM, TEM, and EDS. Based on the experimental results, we propose that the growth of 3D nanostructures is controlled by
the stability of the intermediate chelate complex made by indium(III) and solvent. The optical properties of the 3D β-In2S3 nanostructures were also investigated by UV–Vis and PL spectroscopy, which indicated strong quantum confinement effect. 相似文献
36.
The effect of electron doping on the magnetic properties of the brownmillerite type bilayered compounds has been investigated by neutron powder diffraction in La substituted Ca(2.5-x)La(x)Sr(0.5)GaMn(2)O(8) compounds (x = 0.05 and 0.1), in comparison with the undoped compound (x = 0). In all compounds, a long-range three-dimensional collinear antiferromagnetic (AFM) structure is found below the Néel temperature T(N) of the respective compound, whereas, well above T(N), three-dimensional short-range magnetic ordering is observed. In the intermediate temperature range just above T(N), a strong effect of electron doping (La substitution) on the magnetic correlations has been observed. Here, a short-range AFM correlation with a possible dimensionality of three has been found for substituted compounds (x = 0.05 and 0.1) as compared to the reported two-dimensional long-range AFM ordering in the parent compound. With increasing electron doping, a decrease in T(N) is also observed. The short-range magnetic correlations set in over a large temperature range above T(N). A magnetic phase diagram in the x-T plane is proposed from these results. 相似文献
37.
Vinit K. MittalSantanu Bera S.V. NarasimhanS. Velmurugan 《Applied Surface Science》2011,258(4):1525-1530
Sorption of Sb(III) on carbon steel surface in aqueous medium (pH 2.8) in presence of different oxyanions like molybdate and selenite has been studied. It is observed that the presence of molybdate or selenite in solution reduced Sb(III) adsorption and surface precipitation to a great extent. The solution at different stages of the adsorption experiment has been analyzed by inductively coupled plasma-atomic emission spectroscopy technique. X-ray diffraction and X-ray photoelectron spectroscopy (XPS) techniques have been used to characterize the precipitate layer and the adsorbed layer. A detailed analysis of the XPS data reveals the mechanism involved in the two cases. 相似文献
38.
39.
Srinivas Pasikanti D. Srinivasa Reddy P.K. Dubey Parthasarathi Das 《Tetrahedron letters》2010,51(1):151-152
Synthesis of varenicline the antismoking drug has been achieved in six steps with 10% overall yield. A Diels-Alder reaction, oxidative cleavage of an olefin and reductive amination remain as key steps in the synthesis 相似文献
40.
Carsten Thirstrup Yuan Shi Per B kkelund Bera P alsd ttir 《Fiber and Integrated Optics》1996,15(1):1-6
Modulation of the absorption and refractive index in Er3+-doped fibers for a signal wavelength in the 1550-nm band and a pump wavelength of 980 nm is investigated. The experimental results are compared with a model that takes into account optical transitions between the ground state and the metastable state in Er3+. Good agreement between the experiment and the model is obtained apart from a wavelength-independent constant in the refractive index modulation, which is discussed. 相似文献