Polymorphism of the Ag8S4O4 and Ag6S3O4 compounds

Experimental results of the reaction occurring between aqueous solutions of AgNO₃ and Na₂S₂O₃ were presented in this work. It has been demonstrated that these reagents form two phases to which the summary formulas: -Ag₈S₄O₄ and -Ag₆S₃O₄ were ascribed. The -Ag₈S₄O₄ phase crystallizes in a tetragonal system and has the following parameters of the unit cell: a = b = 0.72052 nm, c = 0.51140 nm, V = 0.26550 nm³, Z = 1, d_x = 6.60 g/cm³. At 223°C -Ag₈S₄O₄ undergoes an irreversible, endothermic polymorphic transition. The heat of this transition amounts 8.03 × 10^–3 J/mol. A high-temperature polymorphic form -Ag₈S₄O₄ melts at 400°C. The -Ag₆S₃O₄ phase crystallizes in a monoclinic system and has the following parameters of the unit cell:a = 2.09616 nm, b = 0.53118 nm, c = 1.49885 nm, = 102.78°, V = 1.62753 nm³, Z = 8, d_x = 6.59 g/cm³. -Ag₆S₃O₄ also undergoes an irreversible, endothermic polymorphic transition at 221°C. The heat of this transition amounts 7.65 × 10^–3 J/mol. A high-temperature form, -Ag₆S₃O₄, melts at 390°C.     

High temperature Raman spectroscopy of silver tetratungstate,Ag8W4O16

Polarized Raman spectra have been obtained on oriented single crystals of Ag₈W₄O₁₆ from 20°C to the melting point (620°C) and also of the melt, both in air and in an oxygen atmosphere. The temperature dependences of the low-frequency Ag⁺-ion vibrations show no anomalies, in contrast to those in ionic conductors such as α-AgI. Polarization versus temperature measurements have been made on the crystals under the same conditions as the Raman measurements. The results indicate that there is decomposition of the crystals in air which produces irreversible conducting phases. The oxygen atmosphere impedes this decomposition, and the results in this case confirm an earlier prediction that there is no crystallographic transformation of the crystals up to the melting point and that the (W₄O₁₆)^8? ions continue to be noncentrosymmetric in the melt.     

Superhyperfine interactions of Ag6+ clusters in silver loaded 4A zeolite

A paramagnetic silver cluster consisting of an octahedral Ag₆⁺ molecule surrounded by a cube of eight Ag⁺ ions has been detected in γ-irradiated zeolite 4A fully loaded with silver. The ‘superhyperfine’ interaction of the silver ions in the outer cage was used as a probe to study the effects on the cluster of dehydration at various temperatures.     

Crystal structures of Ba4CaCu3O8+δ and Ba6CaCu3O10+δ

The crystal structures of the two ternary compounds, Ba₄CaCu₃O_8+δ and Ba₆CaCu₃O_10+δ, have been investigated by means of X-ray diffraction combined with Rietveld analysis. We found that the Ba₄CaCu₃O_8+δ phase has a cubic structure (Im–3m, a=8.1515(1) Å, δ=+0.8) for high oxygen content as reported in the literature but undergoes a transformation into a tetragonal structure (I4/mmm, a=8.1888(1) Å, c=8.0634(1) Å for δ=−0.3) when the oxygen content is lowered. The crystal structure of Ba₆CaCu₃O_10+δ (I4/mmm, a=4.0463(1) Å, c=21.7322(4) Å for δ=+0.2) is confirmed. Changes in the c value with sintering conditions suggest a variable oxygen content with no structure transformation.     

EELS and XPS investigations of Ba2Cu3O4Cl2

Electron energy-loss spectroscopy in transmission and x-ray photoelectron spectroscopy have been applied to investigate single crystalline Ba₂Cu₃O₄Cl₂ to obtain the loss-function along the high symmetry directions of the cuprate plane, the Cu2p and O1s excitation edges, and to study the valence band and the core level electronic structure. The lossfunction shows a gap of 1.65eV, practically dispersionless structures between 2 and 8eV, and a volume plasmon located at 25eV. The dielectric function is derived. The excitation edges are a measure for the number of holes located in the Cu like or O like states parallel or perpendicular to the Cu₃O₄ planes. The Cu₂p_3/2 XPS shows three features in the main line and a satellite structure due to two independent copper sites and indicating a strong 3d electron correlation. By interpreting forward scattering features the valence band structure can be assigned to its atomic origin.     

Dielectric properties of nanophase Ag2HgI4 and Ag2HgI4-Al2O3 nanocomposites

The dielectric properties of nanophase Ag₂HgI₄ and Ag₂HgI₄-Al₂O₃ nanocomposites at different frequencies have been studied over a temperature range covering the stability range of β phase of Ag₂HgI₄ and beyond the β to a phase transition temperature. έ′, tan δ and σ_a.c. of nanophase Ag₂HgI₄ and Ag₂HgI₄-Al₂O₃ nanocomposites were found to be larger than the reported values for polycrystalline pellets of Ag₂HgI₄. The dielectric properties of the nanocomposites were found to be a function of the wt.% of nano alumina. The observed changes are attributed to the grain boundary properties of nanophase materials and to the microsize space charge effects.     

On the microscopic interaction in the Chevrel compounds Cu2Mo6S8 and Mo6Se8

The available data on the superconducting properties of Cu₂Mo₆S₈ and Mo₆Se₈ are used to gain some insight into their microscopic parameters ² F() and *, the electron-photon spectral density and Coulomb pseudopotential, respectively. While thermodynamic data play a prominent role in the analysis, use is also made of information on the generalized phonon frequency distributionG() and, for the case of Cu₂Mo₆S₈, on the second derivative of current-voltage tunneling data. The parameters obtained are tested against upper critical magnetic field data. The work suggests that the electron mass enhancement parameter may be of order 2 with * unusually large.     

Magnetic field-induced superconductivity in the ferromagnetic state of HoMo6S8

The Chevrel-phase HoMo₆S₈ is one of the few known ferromagnetic reentrant superconductors, having an upper superconductive critical temperatureT _c1 =1.78 K, a Curie temperatureT _m =0.75 K, and reentering into a normal ferromagnetic state belowT _c2 =0.64 K. After a brief survey of the characteristic properties of HoMo₆S₈, we present new results obtained by simultaneous resistance and magnetization measurements on a single crystal of HoMo₆S₈, performed in the whole temperature range 35mKT4.2 K and for several orientations of the easy magnetization axis with respect to the applied magnetic field. Magnetic field-induced superconductive transitions are observed well belowT _c2 in the ferromagnetic state. Those transitions can be understood as the first experimental observation of a purely electromagnetic effect earlier suggested by Ginzburg: if the internal field is antiparallel to the spontaneous magnetization, the magnetic induction may be reduced below its critical value and a superconductive transition may take place. It is possible if exchange interactions are negligible; our results concerning the anisotropy of the internal upper critical fieldH _c2 are consistent with that requirement. We also discuss the possible origins for the low-resistance state in zero field: it might be due to domain wall superconductivity.     

An upper limit for the anharmonicity of the cation modes in the superconducting chevrel-phase compounds PbMo6S8 and SnMo6S8

PbMo₆S₈ and SnMo₆S₈ have low-lying phonon modes involving mainly motion of the Pb or Sn cation. It has long been believed that these cation modes are highly anharmonic. By examining the inelastic neutron scattering, x-ray diffraction, and magnetic susceptibility data in the literature, however, it is shown that these modes are nearly harmonic at room temperature. There is no evidence that they are anharmonic at low temperature. From the observed frequency of the cation modes at room temperature, the delocalization of the cation perpendicular to the trigonal axis is calculated. The calculated delocalization agrees well with that indicated by the x-ray diffraction data.     

Composition, Structure, and Thermal Expansion of Ca3Fe4S3O6 and CaFeSO

The iron calcium oxysulfides Ca₃Fe₄S₃O₆ and CaFeSO are synthesized by reacting mixtures of CaO and FeS in an inert atmosphere. Their elemental compositions and lattice parameters are determined by x-ray microanalysis and x-ray diffraction. From the temperature-dependent lattice parameters of the oxysulfides (measured up to 1020 K), their thermal expansion coefficients are evaluated.     

Fe3O4／Ag复合纳米材料的制备及SERS研究

采用乙酰丙酮铁作为有机前驱体盐,在二苄基醚溶液中,以油酸、油胺为表面活性剂,十六醇作为“分解促进剂”,分解前驱体乙酰丙酮铁,制备四氧化三铁纳米颗粒。以四氧化三铁纳米颗粒为“种子”,加入醋酸银,以油胺为还原剂,制备Fe3O4/Ag复合磁性纳米材料。利用透射电子显微镜对纳米材料的形貌进行了表征,通过紫外～可见吸收光谱和拉曼光谱仪对纳米材料的表面增强拉曼散射光谱进行表研究,采用铷硼磁铁对磁性纳米材料的磁性进行初步研究。实验结果表明：FelO2／Ag复合磁性纳米颗粒既具有磁性又具有贵金属光谱特性;相对Fe304而言,Fe3O4/Ag复合纳米粒子具有更好的s隙S增强效果。     

Photoelectrochemical properties of metal-cluster oxide compounds,A2Mo3O8 and (LiY)Mo3O8

PEC studies on the single crystals of the metal-cluster oxide compounds. A₂Mo₃O₈ (A = Zn, Mg, Fe), and polycrystalline LiYMo₃O₈ are reported. The photoresponse behaviour is attributed to the Mod-d transition. The photopotential, the photocurrent vs applied voltage and the wavelength data indicate thatn-Zn₂Mo₃O₈ is stable and possesses a small and indirect band gap of 1·55 eV and a direct band gap of 1·9 eV. With change in A ions in A₂Mo₃O₈, there is no significant change in the PEC properties. LiYMo₃O₈ is found to be ofp-type. PEC studies show that excepting for poor electronic conductivity, A₂Mo₃O₈ possesses all the requisitie characteristics of an ideal photoanode for PAE of water for trapping solar energy.     

Study of the pseudoternary compounds Sn1.2−xErxMo6S8 and SnMo6S8−xSex and their superconducting critical temperatures

The solid solutions Sn_1.2?xEr_xMo₆S₈ and SnMo₆S_8?xSe_x are examined crystallographically and correlations between lattice parameters and superconducting transition temperatures are discussed.     

Ag包覆Fe3O4复合粉体的制备及其性能研究

用化学镀法,甲醛为还原剂,制备Fe3O4/Ag包覆复合粉体.用XRD、SEM和EDX对粉体进行表征.用重法测定粉体的抗氧化性能,并研究了AgNO3用量对Fe3O4/Ag包覆复合粉体的导电性能的影响.结果表明,用该法制备的Fe3O4/Ag包覆复合粉体能够实现表面银层包覆完整;Fe3O4粉镀银后的抗氧化性能得到一定程度的提高;AgNO3用量越多,Fe3O4/Ag包覆复合粉体的导电性能越好.     

Reactivity and powder morphology in YBa2Cu4O8-related compounds synthesis

The factors that allow the synthesis of YBa₂Cu₄O₈ at low oxygen pressures are discussed. The importance of having a homogeneous distribution of initial reacting powders to increase the reaction speed and purity of the final product is shown. Compounds with partial and total substitution of yttrium by thulium are also considered.     

Influence of charge state on product ion mass spectra and the determination of 4S/6S sulfation sequence of chondroitin sulfate oligosaccharides

Electrospray ionization-Fourier transform ion cyclotron resonance tandem mass spectrometry is used to study the influence of charge state on the product ion spectra of chondroitin sulfate oligosaccharides for determination of the sulfate position on N-acetylgalactosamine residues. Sustained off-resonance irradiation collision-induced dissociation and infrared multiphoton dissociation are investigated for tandem mass spectrometry of chondroitin sulfate. Product ion spectra were obtained for ions of varying charge states from (4,5)-unsaturated (delta-unsaturated), reduced delta-unsaturated, and saturated oligosaccharides from chondroitin sulfate A and chondroitin sulfate C, separately. It was observed that ions in which the charge (z) is less than the number of sulfates dissociate to produce predominantly even-numbered B(n), C(n), Y(n), and Z(n) ions, and that odd-numbered fragment ions are observed for ions that have z equal to the number of sulfates. Sulfate adducted ions were observed in the product ion spectra of singly charged tetramer and hexamer oligosaccharides. This sulfate adduction was determined to result from migration of neutral sulfate during excitation.     

The triclinic structure of Cu1.8Mo6S8 in the superconducting state

An x-ray powder diffraction analysis at 5 K shows that the structure of Cu_1.8Mo₆S₈ in the superconducting state is a triclinic distorted version of the rhombohedral room temperature structure. The distortion is due to a clustering of the Cu atoms into pairs [d(Cu-Cu) = 2.58 å] as the compound transforms at 270 K from the disordered high-temperature into the ordered low-temperature modification.