电子型超导体Ln2—xCexCuO4—y的正交相与电子输运结构模型

高温真空X射线衍射实验发现,Sm_(1.85)Ce_(0.15)CuO_(4-y)在715℃时发生T′相向正交相的转变。超导电性测试表明,这个由高温真空退火保存的正交相是一个稍微偏离T′四方结构的超导相(T_(ce)≈10K,a=0.396(1)、b=0.395(0)、c=1.201(4)am)。XPS分析表明,样品中存在Cu~+、Cu~(2+)混合价态。高温真空处理与还原气氛处理一样,可以引进氧离子缺位,适量的氧离子缺位不论对电子型还是对空穴型高T_c超导氧化物都起着十分重要的作用。具体讨论了氧离子缺位在电子型超导体中的作用。提出了一种唯象超导结构模型,解释了一些有关的实验现象。     

La-Ce-Cu系列催化剂SO2中毒机理研究

采用NH_4NO_3共熔法合成La－Ce－Cu系列样品，并通过XRD分析了样品的相组成。XRF证明了系列样品组成均为氧缺陷型化合物．用TEM研究了样品的表面结构，发现随着SO_2中毒的加深，Cu向表面偏析与S结合生成新的化合物，导致了原晶体结构的变形，同时证明纯CeO_2不发生S中毒．XPS研究表明：样品La_(.029)Ce_(0.57)Cu_(0.14)O_x中毒后Cu从La_2CuO_4中分解出来并与S结合生成CuSO_4；相应的CeO_2参与了中毒反应，生成Ce_2O_3,整个中毒反应如下：La_2CuO_4＋2CeO_2＋SO_2＝CuSO_4＋La_2O_3＋Ce_2O_3     

铋系氧化物超导体晶体结构的模拟

自Michel等人首次在Bi-Sr-Cu-O体系中获得7—22 K的Bi_2Sr_2CuO_6超导相以来, 一类新型的双层铋系超导体引起人们的注意, 研究结果表明超导相的转变温度T_c随CuO_2层数的增加而增高. 因此, 晶体结构和超导性之间的关系是人们注意的一个问题. 铋系超导体的晶体完整性很差, 文献仅给出晶体平均结构的晶胞参数. 本文采用原子经验势方法, 对Bi_2Sr_2Ca_(n-1)Cu_nO_(2n+4)(n=1,2,3,4)的理想晶体结构作了模拟计算. 计算了单胞的结构参数和原子的位置参数. 计算表明: Cu-O(3)的原子间距和CuO-BiO的层间距离随n增加而减小. 根据电荷转移模型, 载流子的数目和电导层(CuO_2)及电荷储蓄层(BiO)之间的电荷转移有关. 层间距离的缩短似乎有利于载流子的形成.     

氢致Nd2Fe14B相的层间分裂

Nd_2Fe_(14)B相是一种四方晶相,属P42/mnm(D_(4h)~(14))空间群,可描述为富Nd层和Fe层的交替堆垛层状结构。最近,我们从典型的Nd-Fe-B永磁合金吸放氢后的X射线衍射(XRD)图谱分析发现,Nd_2Fe_(14)B相在吸放氢后其层片间变得极易分裂,稍经研磨即可获得以(001)为解理面的层片状粉末。     

Role of Microstructure and Spectrum Features on the Catalysis Effect of Ce_(1-x)(Nd_(0.5)Eu_(0.5))_xO_(2-δ) Solid Solutions

Nanosized Ce_(1-x)(Nd_(0.5)Eu_(0.5))xO_(2-δ) solid solutions(x = 0.00~0.20) were synthesized by means of hydrothermal method.Then the solid solutions were ball milled with Mg_2Ni and Ni powders for 20 h to get the Mg_2Ni–Ni–5 mol% Ce_(1-x)(Nd_(0.5)Eu_(0.5))xO_(2-δ) composites.The structures and spectrum characteristics of the Ce_(1-x)(Nd_(0.5)Eu_(0.5))xO_(2-δ) solid solutions catalysts were analyzed systemically.XRD results showed that the doped samples exhibited single phase of CeO_2 fluorite structure.The cell parameters and cell volumes were increased with increasing the doped content.Raman spectrum revealed that the peak position of F_(2g) mode shift to higher wavenumbers and the peak corresponding to oxygen vacancies were observed distinctly for the doped samples.UV-Vis technique indicated that the absorption peaks of Eu~(3+) and Nd~(3+) ions appeared; the bandgap energy was decreased linearly.The electrochemical and kinetic properties of the Mg_2Ni–Ni–5 mol% Ce_(1-x)(Nd_(0.5)Eu_(0.5))xO_(2-δ) composites were measured.The maximum discharge capacity was increased from 722.3 mA h/g for x = 0.00 to 819.7 mA h/g for x = 0.16,and the cycle stability S_(20) increased from 25.0%(x = 0.00) to 42.2%(x = 0.20).The kinetic measurement proved that the catalytic activity of composite surfaces and the hydrogen diffusion rate were improved for the composites with doped catalysts,especially for the composites with x = 0.16 and x = 0.20.The catalysis mechanism was analyzed from the point of microstructure and spectrum features of the Ce_(1-x)(Nd_(0.5)Eu_(0.5))xO_(2-δ) solid solutions.     

金属-血清白蛋白的结构研究II. Cu(II)-BSA和Ni(II)-BSA的四 方锥-四方平面 结构

本文用紫外光谱研究Cu(II)-BSA和Ni(II)-BSA配合物的结构随BSA浓度的变化,发现当浓度增大并>2×10^-^4～3×10^-^4mol.dm^-^3时,这两种配合物从五配位的四方锥构型转变成四配位的四方平面构型,首次提供了BSA的Asp羧基氧参与同Cu(II)和Ni(II)配位的证据。计算并讨论了Cu(II),Ni(II)和有关配体轨道的光学电负性。     

金属-血清白蛋白的结构研究II. Cu(II)-BSA和Ni(II)-BSA的四 方锥-四方平面 结构

本文用紫外光谱研究Cu(II)-BSA和Ni(II)-BSA配合物的结构随BSA浓度的变化,发现当浓度增大并>2×10^-^4～3×10^-^4mol.dm^-^3时,这两种配合物从五配位的四方锥构型转变成四配位的四方平面构型,首次提供了BSA的Asp羧基氧参与同Cu(II)和Ni(II)配位的证据。计算并讨论了Cu(II),Ni(II)和有关配体轨道的光学电负性。     

Nd2O3—PbO系中间相的研究

前人研究表明:La_2O_3、Sm_2O_3和Gd_2O_3均与PbO形成通式为RE_2O_3·4PbO的中间化合物。我们曾发现Eu_2O_3-PbO系有一个化学配比约为Eu_2O_(3·)(PbO)_(3.7)的四方结构中间相,Sleight曾报道过Nd_2O_3和PbO能形成不稳定的Nd_2O_3·2PbO化合物,但未对Nd_2O_3-PbO系平衡固相作全面考查,本文报道我们对Nd_2O_(3·)2PbO系中间相的研究结果。 取纯度99.99％的Nd_2O_3和化学纯的PbO,按多种比例研磨混合后压成园柱形样品,     

水合二高碘酸氢合铜(Ⅲ)酸钾钠配合物的合成、结构与光谱性质

本文报道了碱溶液中获得组份为Na_4K[Cu(HIO_6)_2]·12H_2O晶体配合物.用X-射线衍射法测定了晶体结构.晶体属单斜晶系,P2_1/c空间群,a=6.108(2)(?),b=25.055(10)(?),c=14.716(7)(?),β=97.77(3)°,V=2231(2)(?)~3,D_c=2.555g/cm~3,Z=4.晶体中二个畸变的IO_5(OH)八面体与中心铜原子螯合,构成CuO_4平面;Cu—O平均键长为1.83(?);加上CuO_4平面上侧与铜原子形成弱配位的氧原子;共有五个氧原子与铜原子构成近似为C_(2v)点群对称的四方单锥多面体.在碱性水溶液中,配合物的紫外吸收峰的衰减表明,[Cu(HIO_6)_2]~(5-)还原为一级反应.     

超导体Ba_2YCu_3O_(6.92)晶格中不同位置氧的热稳定性

引人注目的Ba_2YCu_3O_(6.0+x)(0.3相似文献   

超导相Tl2Ba2CuO6的制备和晶体结构研究

The superconducting phase Tl_2Ba_2CuO_6 with onset T_C 85 K and zero resistivity at 61 K has been prepared. The unit cell is body-centred tetragonal, space group I_4/mmm, lattice parametrs a=0.3866(1) nm, c=2.3180(3) nm. The relation between structural features and its superconductivity was discussed.     

Dual shell-like magnetic clusters containing Ni(II) and Ln(III) (Ln = La, Pr, and Nd) ions

Dual shell-like nanoscopic magnetic clusters featuring a polynuclear nickel(II) framework encapsulating that of lanthanide ions (Ln = La, Pr, and Nd) were synthesized using Ni(NO3)(2).6H2O, Ln(NO3)(3).6H2O, and iminodiacetic acid (IDA) under hydrothermal conditions. Structurally established by crystallographic studies, these clusters are [La20Ni30(IDA)30(CO3)6(NO3)6(OH)30(H2O)12](CO3)(6).72H2O (1), [Ln20Ni21(C4H5NO4)21(OH)24(C2H2O3)6(C2O4)3(NO3)9(H2O)12](NO3)9.nH2O [C2H2O3 is the alkoxide form of glycolate; Ln = Pr (2), n = 42; Nd (3), n = 50], and {[La4Ni5Na(IDA)5(CO3)(NO3)4(OH)5(H2O)5][CO3].10H2O} infinity (4). Carbonate, oxalate, and glycolate are products of hydrothermal decomposition of IDA. Compositions of these compounds were confirmed by satisfactory elemental analyses. It has been found that the cluster structure is dependent on the identity of the lanthanide ion as well as the starting Ln/Ni/IDA ratio. The cationic cluster of 1 features a core of the Keplerate type with an outer icosidodecahedron of Ni(II) ions encaging a dodecahedral kernel of La(III). Clusters 2 and 3, distinctly different from 1, are isostructural, possessing a core of an outer shell of 21 Ni(II) ions encapsulating an inner shell of 20 Ln(III) ions. Complex 4 is a three-dimensional assembly of cluster building blocks connected by units of Na(NO3)/La(NO3)3; the structure of the building block resembles closely that of 1, with a hydrated La(III) ion internalized in the decanuclear cage being an extra feature. Magnetic studies indicated ferromagnetic interactions in 1, while overall antiferromagnetic interactions were revealed for 2 and 3. The polymeric, three-dimensional cluster network 4 displayed interesting ferrimagnetic interactions.     

Cation deficient layered Ruddlesden-Popper-related oxysulfides La2LnMS2O5 (Ln=La, Y; M=Nb, Ta)

The structures of the new oxysulfide Ruddlesden-Popper phases La2LnMS2O5 (Ln=La, Y; M=Nb, Ta) are reported together with an iodide-containing variant: La3-xNb1+xS2O5I2x (0相似文献   

Unequivocal synthetic pathway to heterodinuclear (4f,4f') complexes: magnetic study of relevant (Ln(III), Gd(III)) and (Gd(III), Ln(III)) complexes

The tripodal ligand tris[4-(2-hydroxy-3-methoxyphenyl)-3-aza-3-buten]amine (LH(3)) is capable of coordinating to two different lanthanide ions to give complexes formulated as [LLnLn'(NO(3))(3)].x H(2)O. The stepwise synthetic procedure consists of introducing first a Ln(III) ion in the inner N(4)O(3) coordination site. The isolated neutral complex LLn is then allowed to react with a second and different Ln' ion that occupies the outer O(6) site, thus yielding a [LLnLn'(NO(3))(3)].x H(2)O complex. A FAB(+) study has confirmed the existence of (Ln, Ln') entities as genuine, when the Ln' ion in the outer site has a larger ionic radius than the Ln ion in the inner site. The qualitative magnetic study of the (Gd, Ln) and (Ln, Gd) complexes, based on the comparison of the magnetic properties of (Gd, Ln) (or (Ln, Gd)) pairs and (Y, Ln) (or (Ln, La)) pairs, is very informative. Indeed, these former complexes are governed by the thermal population of the Ln(III) Stark levels and the Ln-Gd interaction, while the latter are influenced by the thermal population of the Ln(III) Stark levels. We have been able to show that a ferromagnetic interaction exists at low temperature in the (Gd, Nd), (Gd, Ce), and (Yb, Gd) complexes. In contrast, an antiferromagnetic interaction occurs in the (Dy, Gd) and (Er, Gd) complexes. Although we cannot give a quantitative value to these interactions, we can affirm that their magnitudes are weak since they are only perceptible at very low temperature.     

Synthesis, crystal structures, and properties of oxovanadium(IV)-lanthanide(III) heteronuclear complexes

A new series of oxovanadium(IV)-lanthanide(III) heteronuclear complexes [Yb(H2O)8]2[(VO)2(TTHA)](3)21 H2O (1), {[Ho(H2O)7(VO)2(TTHA)][(VO)2(TTHA)](0.5)} 8.5 H2O (2), {[Gd(H2O)7(VO)2(TTHA)][(VO)2(TTHA)](0.5)}8.5 H2O (3), {[Eu(H2O)7][(VO)2(TTHA)](1.5)} 10.5 H2O (4), and [Pr2(H2O)6(SO4)2][(VO)2(TTHA)] (5) (H6TTHA=triethylenetetraaminehexaacetic acid) were prepared by using the bulky flexible organic acid H(6)TTHA as structure-directing agent. X-ray crystallographic studies reveal that they contain the same [(VO)2(TTHA)]2- unit as building block, but the Ln3+ ion lies in different coordination environments. Although the lanthanide ions always exhibit similar chemical behavior, the structures of the complexes are not homologous. Compound 1 is composed of a [Yb(H2O)8]3+ ion and a [(VO)2(TTHA)]2- ion. Compounds 2 and 3 are isomorphous; both contain a trinuclear [Ln(H2O)7(VO)2(TTHA)]+ (Ln=Ho for 2 and Gd for 3) ion and a [(VO)2(TTHA)]2- ion. Compound 4 is an extended one-dimensional chain, in which each Eu3+ ion links two [(VO)2(TTHA)]2- ions. For 5, the structure is further assembled into a three-dimensional network with an interesting framework topology comprising V2Pr2 and V4Pr2 heterometallic lattices. Moreover, 4 and 5 are the first oxovanadium(IV)-lanthanide(III) coordination polymers and thus enlarge the realm of 3d-4f complexes. The IR, UV/Vis, and EPR spectra and the magnetic properties of the heterometallic complexes were studied. Notably, 2 shows unusual ferromagnetic interactions between the VO2+ and Ho3+ ions.     

Study of the luminescent and magnetic properties of a series of heterodinuclear [Zn(II)Ln(III)] complexes

Herein, we report the synthesis, structural investigation, and magnetic and photophysical properties of a series of 13 [Zn(II)Ln(III)] heterodinuclear complexes, which have been obtained employing a Schiff-base compartmental ligand derived from o-vanillin [H(2)valpn = 1,3-propanediylbis(2-iminomethylene-6-methoxy-phenol)]. The complexes have been synthesized starting from the [Zn(valpn)(H(2)O)] mononuclear compound and the corresponding lanthanide nitrates. The crystallographic investigation indicated two structural types: the first one, [Zn(H(2)O)(valpn)Ln(III)(O(2)NO)(3)], contains 10-coordinated Ln(III) ions, while in the second one, [Zn(ONO(2))(valpn)Ln(III)(H(2)O)(O(2)NO)(2)]·2H(2)O, the rare earth ions are nine-coordinated. The Zn(II) ions always display a square-pyramidal geometry. The first structural type encompasses the larger Ln ions (4f(0)-4f(9)), while the second is found for the smaller ions (4f(8)-4f(11)). The dysprosium derivative crystallizes in both forms. Luminescence studies for the heterodinuclear compounds containing Nd(III), Sm(III), Tb(III), Dy(III), and Yb(III) revealed that the [Zn(valpn)(H(2)O)] moiety acts as an antenna. The magnetic properties for the paramagnetic [Zn(II)Ln(III)] complexes have been investigated.     

Preparation, Characterization and Properties of Two New Lanthanide(III)-5-(2-pyridyl)tetrazolate Complexes

Two new mononuclear lanthanide(III) complexes Ln(pytz)3(H2O)3·(H2O)3.5[Ln=Tb(1); Eu(2); Hpytz= 5-(2-pyridyl)tetrazole] were synthesized by reacting Hpytz with the corresponding lanthanide(III) ions and characterized. The single crystal X-ray diffraction analysis reveals that complexes 1 and 2 are isostructural and the lanthanide(III) ions in both complexes 1 and 2 are nine-coordinated, with three oxygen atoms of three coordination water molecules and six nitrogen atoms of three pytz ligands, forming a monocapped square antiprism. Extensive hydrogen bonds exist, resulting in a three-dimensional supramolecular network structure by hydrogen-bonds in both complexes 1 and 2, respectively. Complex 1 exhibits typical green fluorescence of Tb(III) ion and complex 2 red fluorescence of Eu(III) ion, in solid state at room temperature.     

Coordination ability of trans-cyclohexane-1,2-diamine-N,N,N',N'-tetrakis(methylenephosphonic acid) towards lanthanide(III) ions

The proton and metal complex equilibria of trans-cyclohexane-1,2-diamine-N,N,N',N'-tetrakis(methylenephosphonic acid) (CDTP) with lanthanide(iii) ions, where Ln(III) = La(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Ho(III) and Lu(III) were studied. The stoichiometry, protonation and complex formation constants were determined by potentiometric titration at 25.0 degrees C and ionic strength of 0.1 mol dm(-3) (KCl). All metal ions form several species: [LnH4L]-, [LnH3L](2-), [LnH2L](3-), [LnHL](4-), [LnL](5-), [LnH(-1)L](6-) and [LnH(-2)L](7-) in the pH range between 2 and 11. The stability constants log beta(LnL) were found to be between 14.7 and 16.7. The studied complexes were also characterized by spectroscopic methods (31P NMR, UV-Vis absorption and emission spectroscopy). These studies allowed to reveal a distinct structural change of the Ln(III)-CDTP complex which occurs between protonated and hydroxy species in solutions at pH around 7.5. The major change is caused by the involvement of both nitrogen donors in the metal ion coordination occurring in ML species. The data obtained from UV-Vis spectroscopy allowed to draw conclusions about complex symmetry and to estimate a number of coordinated water molecules. The hydration number or more precisely the number of two OH oscillators was found to be approximately one in all species formed over the pH range between 5 and 10. The structure of the major hydroxy complex was supported by X-ray crystallographic data. The crystal structures of the Eu(III) and Tb(III) complexes clearly show that the CDTP ligand is coordinated to the Ln(III) ion by two nitrogen and four oxygen atoms in such a way that only one oxygen atom from each phosphonic group is placed in the lanthanide inner sphere. The monomeric complex anion is connected to a symmetry related ion through short hydrogen bonds formed by two hydroxy ions and one water molecule. In this way the two neighbouring anions form a quasi-dimer in which one of the Ln(III) ion is seven-coordinate (two N atoms, four O atoms and one hydroxy ion) and the other is eight-coordinate (two N atoms, four O atoms, one hydroxy ion and one water molecule).     

NMR study of Li+ ion dynamics in the perovskite Li(3x)La(1/3-x)NbO3

(7)Li and (6)Li nuclear magnetic resonance (NMR) experiments are carried out on the perovskite Li(3x)La(1/3-x)NbO(3). The results are compared to those obtained on the titanate Li(3x)La(2/3-x)TiO3 (LLTO) in order to investigate the effect, on the lithium ion dynamics, of the total substitution of Nb(5+) for Ti(4+) in the B-site of the ABO(3) perovskites. The XRD patterns analysis reveals that this substitution leads to a change in the distribution of the La(3+) ions in the structure. La(3+) ions distribution is very important, in regard to ionic conductivity, because these immobile ions can be considered as obstacles for the long-range Li+ motion. If compared to the titanates, the compounds of the niobate solid solution have a bigger unit cell volume, a smaller number of La(3+) ions, and a higher number of vacancies. These should favor the motion of the mobile ions into the structure. This is not experimentally observed. Therefore, the interactions between the mobile species and their environment greatly influence their mobility. (7)Li and (6)Li NMR relaxation time experiments reveal that the Li relaxation mechanism is not dominated by quadrupolar interaction. (7)Li NMR spectra reveal the presence of different Li+ ion sites. Some Li+ ions reside in an isotropic environment with no distortion, some others reside in weakly distorted environments. T(1), T(1)(rho), and T(2) experiments allow us to evidence two motions of Li+. As in LLTO, T(1) probes a fast motion of the Li+ ions inside the A-cage of the perovskite structure and T(1)(rho) a slow motion of these ions from A-cage to A-cage. At variance with what has been observed in LLTO, these different Li+ ions can be differentiated through the spin-lattice relaxation times, T(1) and T(1)(rho), as well as through the transverse relaxation time, T(2).     

A series of trinuclear Cu(II)Ln(III)Cu(II) complexes derived from 2,6-Di(acetoacetyl)pyridine: synthesis, structure, and magnetism

A series of trinuclear Cu(II)Ln(III)Cu(II) complexes with the bridging ligand 2,6-di(acetoacetyl)pyridine have been prepared by one-pot reaction with Cu(NO(3))(2).3H(2)O and Ln(NO(3))(3).nH(2)O in methanol. X-ray crystallographic studies for all the complexes indicate that two L(2)(-) ligands selectively sandwich two Cu(II) ions with the 1,3-diketonate entities and one Ln(III) ion with the 2,6-acetylpyridine entity to form a trinuclear CuLnCu core bridged by the enolate oxygen atoms. Cryomagnetic properties of the complexes are studied with respect to the electronic structure of the Ln ion.