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101.
Band structure calculations at the level of LMTO-ASA provide insight into the electronic structure of BaV10O15 and the origin of the structural phase transition. A crystal orbital Hamiltonian population/integrated crystal orbital Hamiltonian population analysis provides evidence that the crystallographic phase transition is driven by V-V bond formation. As well, the energy bands near the Fermi level are very narrow, <1 eV, consistent with the fact that the observed insulating behavior can be due to electron localization via either Mott-Hubbard correlation and/or Anderson disorder. The partial solid solution, BaV10−xTixO15, was examined to study the effect of Ti-doping at the V sites on the structure and electronic transport properties. In spite of the non-existence of “BaTi10O15”, the limiting x=8, as indicated by a monotonic increase in the cell volume and systematic changes in properties. This limit may be due to the difficulty of stabilizing Ti2+ in this structure. For x=0.5 both the first order structural phase transition and the magnetic transition at 40 K are quenched. The samples obey the Curie-Weiss law to x=3 with nearly spin only effective moments along with θ values which range from −1090 K (x=0.5) to −1629 K (x=3). For x>3 a very large, ∼2×10−3 emu/mol, temperature independent (TIP) contribution dominates. Conductivity measurements on sintered, polycrystalline samples show semiconducting behavior for all compositions. Activation energies for Mott hopping derived from high temperature data range from ∼0.1 eV for x=0-1 and fall to a plateau of 0.06 eV for x=3-7. Low temperature data for x=3, 5 and 7 show evidence for Mott variable range hoping (VRH) with a T1/4 law and in one case between 5 and 17 K, a Efros-Shklovskii correlated hopping, T1/2 law, was seen, in sharp contrast to BaV10O15 where only the E-S law was observed up to 75 K. Seebeck coefficients are small (<35 μV/K), positive, roughly TIP and increase with increasing x up to x=5. This may point to a Heikes hopping of holes but a simple single carrier model is impossible. The compositions for x>3 are remarkable in that local moment behavior is lost, yet a metallic state is not reached. The failure of this system to be driven metallic even at such high doping levels is not fully understood but it seems clear that disorder induced carrier localization plays a major role. 相似文献
102.
纤维素基磁性聚偕胺肟树脂的研究——循环吸溴中吸附与还原能力的变化 总被引:3,自引:0,他引:3
研究了酸式纤维素基磁性聚偕胺肟树脂(AMAO)在循环吸溴过程中吸附容量和还原能力的变化,发现原树脂的吸溴初速和溴的还原率比再生树脂高一倍以上,但第一次和第二次再生树脂的吸附速度和还原效率几乎相同,暗示着树脂吸溴后基本结构已发生了彻底的变化.树脂在循环使用时吸溴容量变化不大而溴的还原量却显著降低,表明AMAO作为吸溴剂有较高的实用价值. 相似文献
103.
Hong-Chang Yao Song Gao Li-Min Zheng Xin-Quan Xin 《Journal of solid state chemistry》2004,177(12):4557-4563
Hydrothermal reactions of copper (II) nitrate with 1-hydroxycyclohexanephosphonic acid [C6H10(OH)PO3H2] or Δ1-cyclohexenephosphonic acid [C6H9PO3H2] have resulted in three new copper phosphonates, namely, Cu(C6H10(OH)PO3)(H2O)2 (1), Cu(C6H10(OH)PO3) (2) and Cu(C6H9PO3)(H2O) (3). Compound 1 has a dinuclear structure in which two {CuO5} square pyramids are bridged by two {CPO3} tetrahedra through corner sharing. The dimers are connected through intermolecular hydrogen bonds, forming supramolecular layers. Both compounds 2 and 3 show layer structures typical for metal mono-phosphonates, in which the inorganic metal-containing layers are separated by cyclohexane or cyclohexene groups. The magnetic studies show that ferromagnetic interactions are mediated between copper centers in compound 1. In compounds 2 and 3, antiferromagnetic interactions are dominant. 相似文献
104.
Magnetic NiFe particles were synthesized through hydrothermal method using hydrazine as reductant. Composite particles with core-shell structure were further achieved by depositing silicon dioxide generated via carbonation decomposition of sodium silicate solution on the surface of magnetic cores. Characterized by XRD, the Ni9Fe particles are of fcc-type structure, and the structure of magnetic cores in composite particles was maintained despite being covered by SiO2 shell. The existence of SiO2 shells in the composite particles were demonstrated by SEM, EDS and IR. The results from TG and VSM indicated that the shell structure affected the physiochemical properties. The composite particles exhibited remarkable resistance to oxidation in comparison with Ni9Fe particles due to being protected by SiO2 shell. Meanwhile, both of them are soft magnetic materials, but Ms, Mr and Hc in Ni9[email protected]2 particle decreased compared with magnetic NiFe particles. The formation mechanisms of Ni9Fe micro-particles and composite Ni9Fe particles were discussed. 相似文献
105.
High nuclearity paramagnetic, spin-coupled transition metal clusters and grids are fascinating chemists and physicists partly because of their structural beauty, and the challenge of creating them, but also because of their novel physical properties. Magnetic interactions between the spin centers are a primary focus. This review will examine a selection of Mn(II) polynuclear grids and clusters, with nuclearities in the range Mn4 to Mn9. Theoretical treatments of the magnetic properties are discussed, and approaches to solving the exchange problem for ‘large’ spin systems related to computational difficulties. A freely available software package (MAGMUN4.1) is presented as a means of dealing simply with spin-coupled clusters in general, and symmetry reduction methods are discussed briefly as a means of dealing with ‘large’ spin systems. 相似文献
106.
顺磁性聚酯金属配合物的合成及其驰豫性能的研究 总被引:2,自引:0,他引:2
本文通过二乙三胺五乙酸(DTPA)或乙二胺四乙酸(EDTA)的双酸酐与二元醇或二元酚进行聚合反应,制备了两个系列共15种新的聚酯型大分子配体及其顺磁性金属配合物,用核磁、红外光谱以及元素分析表征了配体和配合物的结构。初步试验结果表明,与相应的小分子金属配合物相比,聚酯金属配合物具有较高的弛豫性能。 相似文献
107.
In the process of bulk photopolymerization of styrene initiated by AIBN decomposition polyvinyl benzophenone (PVB) can supply an effective cage for triplet-triplet energy transfer between PVB macromolecules and small molecules of AIBN to influence the molecular weight of polystyrene in weak magnetic field (less than 0.035T), that was different from the case of polyvinyl naphthalene (PVN) which supplied cages for this system only in the stronger magnetic field (more than 0.2 T) studies. It was found that in the same conditions, PVN could exert more tremendous influences on the bulk photopolymerizatiou system of styrene than PVB because in the stronger magnetic field the triplet PVN had much longer life time than PVB. 相似文献
108.
J. Borrs R. Carballo A. Castieiras M. C. Gmez‐Conde M. C. Fernndez‐Vidal J. Nicls 《无机化学与普通化学杂志》2005,631(11):2221-2226
Four new dinuclear copper(II) complexes have been synthesized and have the general formula [Cu2(L)(H2O)2], where L = GLYDTO [N,N′‐bis(carboxymethyl)dithiooxamide], ALADTO [N,N′‐bis(carboxyethyl)dithiooxamide], VALDTO [N,N′‐bis(1‐carboxy‐2‐methylpropyl)dithiooxamide] and LEUDTO [N,N′‐bis(1‐carboxy‐3‐methylbutyl)dithiooxamide]. The complexes were characterized by elemental analysis as well as by IR, electronic and EPR spectroscopy. These techniques provided evidence for the presence of the CuNO2S chromophore. Magnetic susceptibility measurements on all the complexes in the range 4–300 K show the existence of a dominant antiferromagnetic interaction with ?J values greater than 300 cm?1. Thermal decomposition behaviour of the complexes was studied by thermogravimetry. 相似文献
109.
110.
在纳米尺度下构建有序的磁性模板和图形是当前的研究热点之一 [1,2 ] .这种模板在生物样品的分离[1] 、磁电子学研究和信息存储 [2 ] 等领域具有重要意义 .目前 ,光刻 [3] 、微触点印刷 [4 ] 和自组装 [5] 等多项技术已被用来构建各种纳米模板 .1 999年 ,美国西北大学 Mirkin小组 [6 ]发明的 Dip- pen纳米刻蚀技术 (简称 DPN技术 )更在可控组装方面显示出巨大优越性 .这项技术是在一定驱动力作用下 ,使吸附在原子力显微镜 ( AFM)针尖上的分子“墨水”逐渐转移到基底表面上 ,实现纳米模板的可控构建 .与传统技术相比 ,DPN技术可在纳米尺… 相似文献