An investigation of low-field magnetoresistance in the double perovskites Sr2Fe1-xZnxMoO6, x=0, 0.05, 0.15 and 0.25

The electrical, magnetic and transport properties of Zn doped polycrystalline samples of Sr2Fe1-xZnxMoO6 ( x = 0, 0.05, 0.15 and 0.25) with the double perovskite structure have been investigated. The subtle replacement of Fe3+ ions by Zn2+ ions facilitates the formation of a more ordered structure, while further substitution leads to disordered structure because of the presence of a striped phase. Analysis of the x-ray powder diffraction patterns based on Rietveld analysis indicates that the replacement of Fe3+ by Zn2+ ions favours the formation of Mo6+ ions. The spin-glass behaviour can be explained on the basis of the competition between the antiferromagnetic superexchange and the ferromagnetic double-exchange interaction. The low-field magnetoresistance was moderately enhanced at x = 0.05, and its origin was found to be the competition between the decrease of the concentration of the itinerant electrons and the weaker antiferromagnetic superexchange in the antiphase boundaries. An almost linear negative magnetoresistance in moderate field has been observed for x = 0.25. A possible double-exchange mechanism is proposed for elucidating the observations; it also suggests a coexistence of (Fe3+, Mo5+) and (Zn2+, Mo6+) valence pairs.

Study on structure and oxide ionic conductivity for new compound Ce(6-x)Ln(x)MoO(15-delta)

A new compound Ce(6-x)Ln(x)MoO(15-delta) has been synthesized by wet-chemistry method. Their crystal structure and oxide ionic conductivity were characterized by powder X-ray diffraction, Raman, IR spectrum and A.C. impedance technique. The XRD results showed that Ce6MO15-delta, Ce(5)LnMoO(15-delta) have cubic symmetry with Fm3m space group. The refined lattice parameters showed that their lattice constants decrease with the decrease of the ionic radius of Ln(3+). The electrochemical measurements showed that the ionic conductivity of resulting oxides Ce(6-x)Ln(x)MoO(15-delta) have an enhance, which may be a kind of promising material for SOFCs.

Mechanisms of sodium and potassium ions transfer facilitated by dibenzo-15-crown-5 across the water /1,2-dichloroethane interface using micropipettes

The transfer of sodium and potassium ions facilitated by dibenzo-15-crown-5 (DB15C5) has been studied at the micro-water/1,2-dichloroethane (water/DCE) interface supported at the tip of a micropipette. Cyclic volt-ammetric measurements were performed in two limiting conditions: the bulk concentration of Na+ or K+ in the aqueous phase is much higher than that of DB15C5 in the organic phase (DB15C5 diffusion controlled process) and the reverse condition (metal ion diffusion controlled process). The mechanisms of the facilitated Na+ transfer by DB15C5 are both transfer by interfacial complexation (TIC) with 1 : 1 stoichiometry under these two conditions, and the corresponding association constants were determined at log beta(1) = 8.97 +/- 0.05 or log beta(1) = 8.63 +/- 0.03. However, the transfers of K+ facilitated by DB15C5 show different behavior. In the former case it is a TIC process and its stoichiometry is 1 : 2, whereas in the latter case two peaks during the forward scan were observed, the first of which was confirmed as the formation of K (DB15C5)(2) at the interface by a TIC mechanism, while the second one may be another TIC process with 1 : 1 stoichiometry in the more positive potential. The relevant association constants calculated for the complexed ion, K+(DB15C5)(2), in the organic phase in two cases, logbeta(2), are 13.64 +/- 0.03 and 11.34 +/- 0.24, respectively.

新型化合物[Ni(en)_3]_2[Ni(en)_2(H_2O)_2]·[As_6V_(15)O_(42)]·4H_2O晶体的水热合成与表征

多金属氧酸盐因其在医药临床、工业催化、功能材料等方面的广泛应用而引起人们的关注 [1～ 6 ] ,其中 ,有关钒化学的研究一直很活跃 ,钒具有与钼、钨明显不同的结构特性 ,钒可以采取 VO4 ,VO5和VO6 方式配位 ,同时 ,钒的价态可以是 + 3,+ 4和 + 5价 .由于钒可采取多种配位方式及多种价态 ,与钼酸盐和钨酸盐相比 ,钒酸盐更具有结构柔顺性 ,同时易形成低价或混合价态物种 .在以往的文献中 ,有关 P- V- O体系多金属氧酸盐的水热合成的研究已有大量的报道 [7] ,在常规溶液合成中 ,人们已对As- V- O体系进行了相对深入的研究 ,而有关水热合成的研究报道却很少 ,已见报道的砷钒化合物有K6 [As6 V15O4 2 ( H2 O) ]· 6H2 O[8,9] ,[As8V14 O4 2 ( H2 O) 1/2 ]4 - [10 ] ,[As8V14 O4 2 ( X) ]6 - [11] ( X=SO2 - 3,SO2 - 4,H2 O) .为了探究水热条件下 As- V- O体系的反应特性 ,我们开展了这方面的研究工作 ,并取得了突破性进展 .本文采用中温水热技术合成了含有机基团...

二苯基-15-冠-5加速钠离子和钾离子在微米管支撑的微-水/1,2-二氯乙烷界面上的转移反应

玻璃微米管针尖可用于支撑微米级的水/1,2-二氯乙烷（W/DCE）界面,并用来研究二苯基-15-冠-5（DB15C5）加速钠离子和钾离子转移反应的机理和求算其络合物的稳定常数.在两种极限情况下,即水相中金属离子浓度远大于有机相中DB15C5的浓度（DB15C5扩散控制过程）和有机相中DB15C5的浓度远大于水相中金属离子浓度（金属离子扩散控制过程）,循环伏安研究表明,加速钠离子转移反应均发生1∶1（金属离子:载体）的界面络合转移过程,相应的一级络合常数分别为logβ1=8.97±0.05和logβ1=8.63±0.03.而对于加速钾离子转移反应,当 DB15C5扩散控制时发生的是一个1:2的界面络合转移过程,当钾离子扩散控制时,在电位窗内却观察到两个过程:一个较低电位的1∶2的界面络合转移过程和一个较高电位的1∶1界面络合转移过程.两种极限条件下所求算的钾离子和DB15C5的二级络合常数分别为logβ1=13.64±0.03和logβ2=11.34±0.24.

Synthesis and electrochemical characteristics of lanthanide complexes with 2-nitro-5,10,15,20-tetraphenylporphyrin and acetylacetonate

Four lanthanide complexes with 2-nitro-5,10,15,20-tetraphenylporphyrin and acetylacetonate were prepared and characterized by elemental analyses, LR, UV-Visible,H-1 NMR, XPS and molar conductance. The redox properties of the lutetium complex with 2-nitro-5,10,15,20-tetraphenylporphyrin and acetylacetonate in dichloromethane were studied by cyclic voltammetry.

人体血浆中15种超痕量稀土元素的电感耦合等离子体质谱法测定

本文用电感耦合等离子体质谱法测定了人体血浆中的稀土元素。在优化的条件下 ,以内标法测得的各种纯水溶液的检测限在 0 .7(Eu)～ 5 .4(Gd) ng·L- 1范围内。研究了 K,Na,Ca,Fe等基体元素对稀土测定的影响。以 In为内标元素补偿样品基体效应以及灵敏度飘移。比较了直接稀释、HNO3- H2 O2 消解及 HNO3-HCl O4消解 3种样品处理方法 ,用 1% HNO3直接稀释样品可满足轻稀土元素的定量分析要求 ,方法的定量测定下限≤ 1μg·L- 1。

Investigation on moleculare and crystal structures of metal complexes with aminopolycarboxylic acids (VII) - Syntheses and structure determination of Na-3[Hg (I) (edta) C1] center dot 6H(2)O

In this paper we describe the moleculare and crystal structures of the Na-3[Hg( II )(edta)Cl] . 6H(2)O (edta=ethylenediamine-N,N,N',N'-tetraacetate). The crystal data are as follows: orthorhombic, a=8. 083 (2) Angstrom , b=13. 870(3) Angstrom , c=38. 617(5) Angstrom , v=4329. 4 (13) Angstrom(3) , Z=8, Dc= 1. 798 g . cm(-3), mu=5. 564 mm(-1), P(000)=2280, R=0. 0317 and R-w=0. 0731 for 3883 unique reflections. In complex, the complex anion [Hg ( II ) (edta)Cl](3-) has a seven-coordination structure like a mono-capped trigonal-prism (C-2v-MTP) in which the edta(4-) acts as a hexadentate ligand with four O atoms and two N atoms and a Cl- caps a quadrilateral face as a seventh ligand. It can be known that the Hg2+ which has a d(10) electronic structure can form a high-coordinate compound with a hexadentate ligand (edta) because it has a big ionic radius.