含二茂铁聚苯胺德合成及电－磁性能研究

本论文将二茂铁基团引入聚苯胺链，合成导电或导磁聚苯胺。取得的主要结果如下： 1、合成了抗磁性的二茂铁单磺酸并用于掺杂聚苯胺，掺杂态聚苯胺的电导率可达2.34´10-1 S/cm，二茂铁单磺酸氧化后掺杂聚苯胺的电子顺磁共振(EPR)上出现了g» 4的新信号。二茂铁单磺酸被FeCl3氧化后，随氧化程度的增加，室温电导率下降1-2个数量级，但材料的磁化率增加，表现出宏观反铁磁性。用I2氧化二茂铁单磺酸掺杂的聚苯胺，其电导率为4.50´10-2 S/cm，在低温下具有铁磁性耦合，外斯温度为15 K。 2、合成了两种草酸根桥联的双金属阴离子与导电聚苯胺的杂化材料。杂化材料同时具有反铁磁性和导电性，外斯温度分别为-19.16 K和-22.10 K，电导率分别为4.8×10-3S/cm和1.2×10-5S/cm。 3、合成了聚邻、间位二茂铁苯胺。可溶的聚邻二茂铁苯胺显示铁磁性，外斯温度为25 K，饱和磁强度为6.89 emu/g。与碘或四氰基对苯醌二甲烷（TCNQ）反应所得配合物的外斯温度分别提高到50 K和104 K，饱和磁强度分别为6.51 emu/g 和4.36 emu/g，在低温下观察到了反铁磁性耦合。难溶的聚间二茂铁苯胺显示宏观抗磁性。 关键词：二茂铁单磺酸，导电导磁性聚苯胺，聚邻二茂铁苯胺，铁磁性耦合

层状钙钛矿结构化合物的合成、电性和磁性的研究

近年来，随着金属多层膜，磁隧道结和钙钦矿锰氧化物等材料中磁阻现象的发现，以研究磁阻效应的机理和应用为目的的磁电子学迅速发展。这其中钙钦矿结构的稀土锰氧化物以其超大的磁阻值和丰富的物理内涵而备受瞩目。尽管人们对此已做了大量的工作，但是对这类氧化物的深入认识直至超大磁电阻效应物理机制的合理解释仍需做艰苦细致的努力。本论文选择层状钙钦矿稀土锰氧化物作为研究对象，系统地研究了A位，B位的变化和B位原子之间的相互作用对氧化物的结构、磁性和磁阻性质的影响。希望得到钙钦矿中磁、电性质和磁阻与结构之间的关系，能对该系列化合物中电、磁性质的变化规律和相互作用机理作出合理的解释。基于LaSr2Mn2O7的结构特殊性，我们选择了它作为母体化合物。并通过过渡金属离子Cr，Ti，Ni，Fe对Mn离子取代来研究B位原子的变化对性质的影响。结果发现，Cr3＋因为与Mn4＋具有相同的电子形态而能够参与双交换作用，使掺杂Cr3＋的系列样品的磁化强度随cr含量的增加而增加。而掺杂讨＋，Ni2＋，Fe3＋离子的化合物虽然与Mn离子之间的相互作用各不相同，但引起的磁性变化却是相同的。这四种元素的掺杂都提高了体系的磁阻和电阻率。通过对这几种过渡金属取代的比较，发现在LaS2Mn2O7中对Mn离子进行取代的离子和Mn离子之间的交换作用对磁性质的影响并不起主要作用，掺杂引起的主要作用是致使Mn位的无序度增加和对双交换作用的稀释和阻碍。值得注意的是每个系列样品中都有一个样品的磁阻在高温时出现较大的正值，且随着温度的降低转变为负值。例如，在Fe掺杂的系列样品中，只有x＝0.2的样品表现出正磁阻，且MR在28OK时达到74％。这可能是因为掺杂导致的结构变化引起的。这种正磁阻对材料的应用意义重大。电荷有序对磁阻材料是一种很重要的状态，为了提高LasrZMn2O7的电荷有序温度，我们选择了具有孤对电子的Bi3+来取代Sr2+。结果发现，单相样品只能持续到x≤0.2。样品的电荷有序温度并没有象预想的那样有所提高。这是因为体系的二维结构抑止了Bi3＋离子的作用，同时由于体系中Bi3＋的含量较少没有达到提高电荷有序温度的程度。但Tco降低的程度相对于其它离子的取代效果（如Gd）要低。目前n=3的层状钙钦矿研究较少，但是由于该化合物具有结构可变性和理论上可以解释磁转换机理，我们对（La，ca）4kMn3O10进行了深入的研究。在La3-3xCa1＋3xMn3O10（0.5≤x≤1.0）中随La3＋含量的减少，该系列化合物经历了从铁磁性到顺磁性再到反铁磁性的转变，同时在磁阻上也经历了由负磁阻（x＝0.5～0.7）到正磁阻（x=0.8-1.0）的转变。根据磁性和电性的变化规律，我们认为这种正负磁阻的转变是由于体系中超交换和双交换作用的相互竞争引起的。La3＋含量多时，Mn3十离子含量较多，双交换作用占主导地位，产生负磁阻；随着Mn3+离子含量的减少，双交换作用逐渐减弱，Mn4+离子之间的反铁磁性超交换作用逐渐增强，产生了正磁阻。在低掺杂浓度时LaxCa4-xMn3O10（x＝0-0.9）经历了顺磁性到反铁磁性的转变，为了了解其磁性变化过程，我们进一步研究了富含Mn4＋的这一区间。发现磁化强度在x≤0.2的范围内随x增加而增强，在高于0.2的掺杂范围后随x的增加而逐渐降低。这是因为这一区间的磁结构由基态时的G型-AFM向x＝0.9时的C型-AFM的转变。而且这种转变与载流子浓度密切相关。

CALCULATION OF SPIN-REORIENTATION TEMPERATURE IN ND2FE14B

The spin-reorientation phenomenon in Nd2Fe14B has been investigated using an angular dependent free energy approach. A magnetic Hamiltonian which includes the crystal electric field term and the exchange term has been established using realistic band structure results. The temperature dependence of the molecular field is accounted for by introducing the Brillouin function and the magnetic Hamiltonian is diagonalized within the ground state multiplet of the Nd ion. The eigenstates are then used to form the partition function for the free energy. At each temperature, the direction of the molecular field is obtained by searching for the minimum in the angular parameter space of the free energy. Our calculations show that for Nd2Fe14B, the net magnetic anisotropy direction is canted away from the c axis at a temperature close to the experimentally reported spin-reorientation temperature of 150 K. The temperature dependence of the magnetic structure is found to be very sensitive to the size of the second order crystal field parameter B20.

Mossbauer spectroscopy study of Fe-57 in R3Fe29-xTx (R=Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

Fe-57 Mossbauer spectra for the Fe atoms in the R3Fe29-xTx (R=Y, Ce, Nd, Sm, Gd, Tb, Dy; T=V, Cr) compounds were collected at 4.2 K. The analysis of Mossbauer spectra was based on the results of magnetization and neutron powder diffraction measurements. The average Fe magnetic moments at 4.2 K, deduced from our data, are in accord with magnetization measurements. The average hyperfine field of Tb3Fe29-xCrx (x=1.0, 1.5, 2.0, and 3.0) decreases with increasing Cr concentration, which is also in accordance with the variation of the average Fe magnetic moment in the Tb3Fe29-xCrx compounds.

Assembly of the highest connectivity Wells-Dawson polyoxometalate coordination polymer: the use of organic ligand flexibility

Through tuning the length of flexible bis(triazole) ligands and different metal ion coordination geometries, four Wells-Dawson polyoxoanion-based hybrid compounds, [Cu-6(btp)(3)(P2W18O62)] center dot 3H(2)O (1) (btp = 1,3-bis(1,2,4-triazol-1-yl)propane), [Cu-6(btb)(3)((P2W18O62) center dot 2H(2)O (2), [Cu-3(btb)(6)(P2W18O62)] center dot 6H(2)O (btb = 1,4-bis(1,2,4-triazol-1-yl)butane) (3), and [Cu-3(btx)(5.5)((P2W18O62) center dot 4H(2)O (btx = 1,6-bis(1,2,4-triazol-1-yl)hexane) (4), were synthesized and structurally characterized. in compound 1, the metal-organic motif exhibits a ladder-like chain, which is further fused by the ennead-dentate [P2W18O62](6-) anions to construct a 3D structure. In compound 2, the metal-organic motif exhibits an interesting Cu-btb grid layer, and the ennead-dentate polyoxoanions are sandwiched by two Cu-btb layers to construct a 3D structure

Studies on the magnetism of cobalt ferrite nanocrystals synthesized by hydrothermal method

Fe-Co/CoFe2O4 nanocomposite and CoFe2O4 nanopowders were prepared by the hydrothermal method. The structure of magnetic powders were characterized by X-ray diffraction diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermal gravity analysis (TGA) and differential thermal analysis (DTA) analysis, X-ray photoelectron spectrometry (XPS), and Fourier transform infrared spectra (FTIR) techniques, while magnetic properties were determined by using a vibrating sample magnetometer (VSM) at room temperature.

Hydrothermal synthesis of lanthanide fluorides LnF(3) (Ln = La to Lu) nano-/microcrystals with multiform structures and morphologies

Lanthanide fluoride LnF(3) (Ln = La to Lu) nano-/microcrystals with multiform crystal structures (hexagonal and orthorhombic) and morphologies (separated elongated nanoparticles, aggregated nanoparticles, polyhedral microcrystals) were successfully synthesized by a facile, effective, and environmentally friendly hydrothermal method. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and photoluminescence spectra were used to characterize the samples. The experimental results indicated that the use of NaBF4 is indispensable for obtaining LnF(3) crystal structures.

Constructing porous frameworks from one-dimensional cobalt-oxygen clusters and pyridinedicarboxylate ligands adopting two rare coordination modes

A porous material with cobalt-oxygen cluster framework has been synthesized hydrothermally, which possesses large and rigid channels and manifests strong antiferromagnetic interactions, and the pyridinedicarboxylate ligand exhibits two types of rare coordination modes.

Construction of coordination networks with high connectivity: a new 8-connected self-penetrating network based on tetranuclear metal clusters

Two highly connected cobalt(II) and zinc(II) coordination polymers with tetranuclear metal clusters as the nodes of network have been prepared, being the first example of an 8-connected self-penetrating net based on a cross-linked alpha-Po subnet.

A Unique Mn2Gd2 Tetranuclear Compound of p-tert-Butylthiacalix[4]arene

A calixarene complex with tetragonal (Mn2Gd2III)-Gd-II tetranuclear units was synthesized in solvothermal conditions, where the addition of a small amount of water was crucial for the formation of the target compound. In the structure, two tail-to-tail p-tert-butylthiacalixarenes are located in a C-shaped mode with a dihedral angle of 14.29 degrees but not in the conventional antiparallel arrangement and form a sandwich-like subunit with an in-between Mn2Gd2 unit. Both calixarenes assume similar cone shapes of C-2v symmetry but are pinched to different extents.

A strategy to prepare ultrafine dispersed Fe2O3 nanoparticles

In this article, a novel strategy was applied to prepare dispersed ultrafine alpha-Fe2O3 nanoparticles. The initial Fe(OH)(3) nanoparticles were synthesized by the reaction of NaOH and FeCl3 in alcohol. With the new-formed nanoparticles as nuclei, NaCl crystallized and encapsulated the particles into solid cages. As a result, the nanoparticles were prevented from aggregating and growing. The composite of Fe(OH)(3) and NaCl was calcined and then washed by water to obtain the pure alpha-Fe2O3 nanoparticles.

Fabrication and characterization of uniform Fe3O4 octahedral micro-crystals

Uniform Fe3O4 octahedral microcrystals with perfect appearance have been successfully synthesized by a Triton X100-assisted polyol process. During the polyols process for the preparation of Fe3O4 octahedra. the introduction of Triton X100 decreases significantly the needed concentration of NaOH. The results show that Fe3O4 octahedra are composed of eight triangular sheets, which are equilateral triangles. The edge size of Fe3O4 octahedron is about 4 mu m. The magnetic properties of Fe3O4 octahedral particles were evaluated on a SQUID magnetometer at room temperature.

Synthesis and Crystal Structure of a New 3D Copper B-Paradodecatungstate Compound: [Na-2(H2O)(8)][Na-8(H2O)(20)][Cu(en)(2)][W12O42] center dot 3H(2)O

A new polyoxotungstate complex [Na-2(H2O)(8)][Na-8(H2O)(20)][Cu(en)(2)][W12O42] center dot 3 H2O (1) (en = ethylenediamine) has been synthesized in aqueous solution and characterized by elemental analysis, IR spectroscopy and TG analysis, together with a single crystal X-ray diffraction study. In compound 1, the Cu(en)(2)(2+) complex cation links the [W12O42](12-) anions to form a I D chain, and the ID chains are further interconnected with Na-8(H2O)(20)(8+) and Na-2(H2O)(8)(2+) cations to construct a new 3D framework.

Two Mn(2)(II)Ln(4)(III) (Ln = Gd, Eu) hexanuclear compounds of p-tert-butylsulfinylcalix[4]arene

Two 3d-4f heterometallic compounds of p-tert-butylsulfinylcalix[4] arene were synthesized by the solvothermal method and characterized by some hinged double-dumbbell-like subunits in which two perpendicular dumbbell entities were constructed by an in-between isosceles triangle Mn(II)Ln(2)(III), and two tail-to-tail calixarene molecules, and hinged by the lanthanide-sulfinyl group bonding. The magnetic properties of the title compounds were examined.

Constructing mixed-metal coordination polymers from copper(II)-pyridinedicarboxylate metalloligands

In the mixed-metal complex catena-poly[bis[diaquasilver(I)] [bis[aquacopper(II)]-mu(3)-pyridine-2,5-dicarboxylato-2': 1: 1'kappa N-5,O-2: O-5: O-5, O-5'-mu-pyridine-2,5-dicarboxylato-2: 1 kappa(4) N, O-2: O-5, O-5'-disilver(I)-mu(3)-pyridine-2,5-dicarboxylato-1: 1': 2 '' kappa(5) O-5, O-5': O-5: N, O-2-mu pyridine-2,5-dicarboxylato-1': 20 ''kappa(4) O-5, O-5': N, O-2] hexahydrate], {[Ag(H2O)(2)][AgCu(C7H3NO4)(2)(H2O)] center dot 3H(2)O}(n), a square-pyramidal Cu-II center is coordinated by two N atoms and two O atoms from two pyridine-2,5-dicarboxylate (2,5-pydc) ligands and a water molecule, forming a [Cu(2,5-pydc)(2)-( H2O)](2-) metalloligand. One Ag I center is coordinated by five O atoms from three 2,5-pydc ligands and, as a result, the [Cu(2,5-pydc)(2)(H2O)](2-) metalloligands act as linkers in a unique mu(3)-mode connecting Ag-I centers into a one-dimensional anionic double chain along the [101] direction.