Phase Diagram of RbI-SmI_2 Binary System and Structural Investigation of RbSm_2I_5 and RbSmI_3

The RbI-SmI2 , binary system was studied with DTA and X-ray powder diffraction. Its phase diagram shows that it has a congruently melting compound,RbSm2I5 , with a melting point 524℃; an incongru-ently melting compound, Rb2SmI4 , with an inconsruently point 467℃ and two compounds, RbSmI3, and Rb3SmI5, being decomposed at 433℃ and 460℃, respectively. The measured structure of RbSm2I5 shows that it is isomorphous with NH4 Pb2 Cl5 space group P21/c, a=10 . 063(3)A, b=9.003(3)A. c =14 . 242(5)A°,β=90.23(3)°;z = 4, MVx= 1 94 . 3cm3/mol;D=5.255g/cm3 and Do =5. 334g/cm3 (25. 0℃).The structural, investigation ofRbSmI3 shows that it belongs to the orthorhombic system with a = 15.914(6)A, b=8.898(3)A c =12.193(5)A; Z=8, MVx =130.0cm3/mol, Dx =4 . 743g/cm3,Do = 4.597g/cm3(25.0℃).     

An efficient and economical synthesis of 5-substituted 1H-tetrazoles via Pb(II) salt catalyzed [3+2] cycloaddition of nitriles and sodium azide

A simple, mild and efficient method is developed for the synthesis of 5-substituted 1H-tetrazoles. Out of three used Pb(II) catalysts, lead chloride (PbCl₂) has been found to be an efficient catalyst for [3+2] cycloaddition of NaN₃ with aromatic and aliphatic nitriles to afford 5-substituted 1H-tetrazoles. The catalyst is reusable up to four cycles with consistent activity. The cost effectiveness and easy availability of the catalyst, simple methodology, excellent yield and easy work-up are the additional advantages.     

Electron radiation effects on the structure of ultradisperse polytetrafluoroethylene

Electron radiation effects (40 mrad, 70 mrad, and 100 mrad) on the molecular and supramolecular structure and morphology of ultradisperse polytetrafluoroethylene obtained by the thermogas dynamic (TGD) method were studied by IR and EPR spectroscopy, X-ray phase analysis, and atomic force microscopy. Irradiation of ultradisperse powder in air leads to oxidized polymer forms due to the terminal carbonyl groups and stable peroxide radicals that appear in the structure. Fast electron radiation in doses of up to 100 mrad did not change the polymer crystallinity and particle entity, while thin films on the surface of ultradisperse polytetrafluoroethylene powder decomposed.     

Silver Molecularly Imprinting Polymer for the Determination of p-Nitroaniline by Surface Enhanced Raman Scattering

Molecular imprinting and surface enhanced Raman scattering (SERS) were used to prepare a core-shell Ag@molecularly imprinting polymer (MIP) for the determination of p-nitroaniline. The obtained Ag@MIP exhibits a detection limit of 10^?12 M, which demonstrates higher sensitivity toward p-nitroaniline than conventional approaches. In addition, the Ag@MIP shows good recyclability, and simultaneously offers better stability and high SERS activity for recognizing target molecules. To characterize the high SERS activity of the SERS-MIP hybrid material, a possible mechanism for the SERS substrate is proposed involving enhancement by the MIP. This study is expected to provide an alternative approach for the determination of p-nitroaniline in aqueous environments.     

Characterization of some new alkali metal molybdate hydrates by thermal and X-ray methods

Preparation and characterization of four new hydrated alkali metal molybdates Na₂Mo₄O₁₃·6H₂O, K₂Mo₄O₁₃·3H₂O, Rb₂Mo₄O₁₃·2H₂O and Cs₂Mo₄O₁₃·2H₂O are described. The compounds were prepared by crystallizing the solution obtained by dissolving MoO₃ and corresponding alkali metal carbonates A₂CO₃ or molybdate A₂MoO₄ in stoichiometric amount in distilled water. The hydrated molybdates were characterized by thermal (TG/DTA) and X-ray diffraction (XRD) methods. The number of water molecules in the compounds were determined from their TG /DTA curves recorded in air and identification of their dehydration products was done by XRD. The cell parameters of the compounds were obtained by indexing their XRD patterns. Attempt to prepare the corresponding hydrated compound of lithium was not successful. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structural and electrical changes in NdSrNiO4−δ by substitute nickel with copper

A novel series of the formula NdSrNi_1−xCu_xO_4−δ were synthesized for various values of x ranging from 0 to 1 in 1 atm of O₂ gas flow using conventional solid-state methods and were characterized by powder X-ray diffraction and electrical resistivity measurements. The compounds have been shown to adopt the K₂NiF₄-type structure. The oxygen stoichiometry of the compounds was determined from thermo-gravimetric analysis (TGA). An analysis of the micro-structure of the neodymium strontium nickel copper oxide is described. All the samples were semi-conducting from room temperature down to 77 K. The effect of Cu²⁺ incorporation on the structural and electrical properties of NdSrNi_1−xCu_xO_4−δ, 0?x?1, are discussed in terms of Jahn-Teller distortion of the (Ni/Cu)O₆ octahedra and mixed valence character of copper.     

含过量钛的 BaO·TiO粉末的高温X射线衍射研究

本文采用高温X射线衍射方法研究了含有过量TiO_2的BaTiO_3粉末在不同温度下的物相关系,并对实验结果进行了分析和讨论。     

Studies on the phase properties of lyotropic liquid crystals of Brij35/sodium oleate/oleic acid/water system:By means of polarizing microscope,SAXS,~2H-NMR and rheological methods

The pseudo-quaternary phase diagram of Brij35/sodium oleate/oleic acid/water systems has been investigated, and the liquid crystal area has been identified, which covers about two thirds of the whole phase diagram. The liquid crystal structure and behavior have been also studied by using polarizing texture, small angle X-ray scattering, 2H-NMR and rheometer etc. The result shows that when the composition of the system changes along the line of AA′ in this large liquid crystal region, the structural change is cubic→cubic/lamellar→lamellar→lamellar/hexagonal→hexagonal. Meanwhile, we made the first attempt of systematic study of the rheological properties of the above system. The lattice constants of cubic and hexagonal liquid crystals are 10.53 and 5.68 nm, respectively.     

Mild hydrothermal synthesis of the two compounds [SrZn2(SeO3)3] and [SrZn0.68Cu0.32(SeO3)2]: Structural characterization,spectroscopic and magnetic studies

Two new selenite SrZn₂(SeO₃)₃ (1) and SrZn_0.68Cu_0.32(SeO₃)₂ (2) were synthesized by the hydrothermal technique under autogeneous pressure. The crystal structure of both compounds was solved from X-ray diffraction data. Compound (1) was crystallized in P$\overline{1}$ triclinic space group. However, compound (2) was crystallized in P2₁/n monoclinic space group. Infrared studies confirm the presence of all vibration bands in both structures. The temperature dependence of the magnetic susceptibility was measured in the temperature range of 10–300?K at different magnetic field intensities for both compounds. No magnetic properties were detected for compound (1). Mean while, compound (2) displayed antiferromagnetic properties.     

热处理对钙钛矿锰氧化物La_(0.95)Sr_(0.05)MnO_3离子价态和磁结构的影响

对于磁性氧化物的磁有序,传统的观点用超交换相互作用(SE)和双交换相互作用(DE)模型进行解释,其出发点都建立在全部氧离子是-2价的基础上.例如,对于LaMnO_3,认为其中的La和Mn都处于+3价,用SE模型解释相邻Mn~(3+)离子间的反铁磁序;当以二价的Sr离子替代一部分La离子后,认为等量的Mn~(3+)离子变为Mn~(4+)离子,用DE模型解释相邻Mn~(3+)和Mn~(4+)离子间的铁磁序.然而,事实上在氧化物中存在一部分负一价氧离子.Cohen[Nature 358 136]利用密度泛函理论计算了BaTiO_3的价电子态密度,结果得到只有Ba离子的化合价与传统观点相同,为+2价;而Ti和0分别为+2.89价和-1.63价,不是传统观点的+4价和-2价,但是与多年来关于氧化物电离度的研究[Rev.Mod.Phys.42 317]和X射线光电子谱(XPS)的研究结果相符合.本文经过不同热处理条件制备了名义成分为La_(0.95)Sr_(0.05)MnO_3的三个样品,通过对样品的XPS分析,发现样品中不存在Mn~(4+)离子,只存在Mn2+和Mn~(3+)离子,平均价态随热处理程序的增加而升高.尽管三个样品有相同的晶体结构,但磁矩明显不同.对于这样的性能,不能用SE和DE模型解释其磁结构.利用本课题组最近在研究尖晶石结构铁氧体磁有序过程中提出的O 2p巡游电子模型解释了这种现象,利用样品在10 K的磁矩估算出的Mn离子平均价态变化趋势与XPS分析结果一致.O 2p巡游电子模型的出发点建立在氧化物中存在一部分负一价氧离子的基础上,这是其与SE和DE模型的根本区别.