Tunneling spectroscopy on the superconducting Chevrel-phase compounds Cu1.8Mo6S8 and PbMo6S8

The Chevrel-phase compounds PbMo₆S₈ and Cu_1.8Mo₆S₈ have been investigated by tunneling spectroscopy. These superconductors show a very strong electron-phonon interaction expressed by 42₀/kT _c5. Structures in the tunneling density of states have been observed at most energies where the phonon spectra show maxima. The coupling of high-energy modes of the Mo₆S₈ units and of modes associated with displacements of the Pb (Cu) atoms are discussed.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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。     

The carboxylate magnetic – Zinc based metal-organic framework heterojunction: Fe3O4-COOH@ZIF-8/Ag/Ag3PO4 for plasmon enhanced visible light Z-scheme photocatalysis

In this work, magnetic nanoparticles (MNPs) grafted with carboxylic acid (Fe₃O₄-COOH MNPs) were successfully prepared from incorporation of glutaric anhydride as a functional group on the surface of the ferrite NPs. The MNP was used as a template to induce the growth of ZIF-8 metal–organic framework (MOF) on its surface. The Fe₃O₄-COOH@ZIF-8 core-shell was incorporated with silver phosphate (Ag₃PO₄) and Ag nanoparticles (Ag NPs) to develop a visible light active Fe₃O₄-COOH@ZIF-8/Ag/Ag₃PO₄ photocatalyst. The materials were characterized using a range of techniques. The photocatalytic activity was investigated systematically by degrading an organo-phosphorus pesticide, diazinon under visible light irradiation. Among synthesized samples, the Fe₃O₄-COOH@ZIF-8/Ag/Ag₃PO₄ heterostructured system exhibited highest photocatalytic activity and improved stability compared to others for the degradation of diazinon under visible light. The superior activity and improved stability of this heterostructured photocatalyst was attributed to the synergistic effects from surface plasmon resonance (SPR) of Ag NPs and sequential energy transfer via Z-scheme mechanism, for effective separation of electron-hole pairs. Radical-trapping experiments demonstrate that holes (h⁺) and O₂⁻ are primary reactive species involved in photocatalytic oxidation process. Moreover, the Fe₃O₄-COOH@ZIF-8/Ag/Ag₃PO₄ photocatalyst did not show any obvious loss of photocatalytic activity during five cycle tests, which indicate that the heterostructured photocatalyst was highly stable and can be used repeatedly. Therefore, the work provides new insights into the design and fabrication of metal-organic frameworks (MOFs) for use as a visible light photocatalyst for degrading organic contaminants.     

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.     

Itinerant electron magnetism in the Mo4 tetrahedral cluster compounds GaMo4S8, GaMo4Se8, and GaMo4Se4Te4

The specific heat and magnetic properties of GaMo₄X₈ (X=S, Se, SeTe) between 1.4 and 290 K are reported. Our measurements tend to demonstrate that these compounds have a very high density of states, leading to a Stoner magnetic instability of conduction electrons at low temperatures. The linear temperature-dependent term in the specific heat is enhanced by electron-phonon coupling and spin fluctuation effects. These compounds could indicate an electron-phonon contribution to the Stoner enhancement factor.     

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.     

Phase equilibria in the pseudoternary system Ag2Se-Ag8GeSe6-Ag8SnSe6

Phase equilibria in the Ag₂Se-Ag₈GeSe₆-Ag₈SnSe₆ system have been studied by differential thermal analysis, X-ray diffraction, scanning electron microscopy, and emf measurements on concentration cells with Ag₄RbI₅ as a solid electrolyte. We have mapped out the T-x phase diagram of the constituent binary system Ag₈GeSe₆-Ag₈SnSe₆, those of two mutually perpendicular sections, and the liquidus projection. The two crystalline phases of the constituent selenides Ag₈GeSe₆ and Ag₈SnSe₆ have been shown to form a continuous series of solid solutions. The Ag₂Se-Ag₈GeSe₆-Ag₈SnSe₆ system is a pseudoternary section through the quaternary system Ag-Ge-Sn-Se, and its phase diagram has a univariant eutectic.     

Novel magnetically separable g-C3N4/Fe3O4/Ag3PO4/Co3O4 nanocomposites: Visible-light-driven photocatalysts with highly enhanced activity

In this study, a series of novel quaternary g-C₃N₄/Fe₃O₄/Ag₃PO₄/Co₃O₄ nanocomposites were fabricated. The prepared nanocomposites were characterized by XRD, EDX, SEM, TEM, UV-DRS, FT-IR, PL, TG, and VSM methods to gain insight about structure, purity, morphology, optical, thermal, and magnetic properties. Photocatalytic activity of the samples was investigated under visible-light irradiation by degradations of rhodamine B, methylene blue, methyl orange, and phenol as four organic pollutants. The highest photocatalytic degradation efficiency was observed when the sample calcined at 300 °C for 2 h with 20 wt% of Co₃O₄. The photocatalytic activity of this nanocomposite is almost 16.8, 15.7, 4.6, and 5.1 times higher than those of the g-C₃N₄, g-C₃N₄/Fe₃O₄, g-C₃N₄/Fe₃O₄/Ag₃PO₄ (20%), and g-C₃N₄/Fe₃O₄/Co₃O₄ (20%) samples in photodegradation of rhodamine B, respectively. Finally, on the basis of the energy band positions, the mechanism of enhanced photocatalytic activity was discussed.     

Electrical resistivity and superconductivity in the chevrel phase compounds of the type Cu1.8Mo6S8—ySey (0 ⩽ y ⩽ 8) and Cu1.8Mo6S8—y Tey, (0 ⩽ y ⩽ 4)

The superconducting transition temperatures and normal state residual electrical resistivities of the ternary Chevrel phase compounds Cu_1.8Mo₆S_8-YSe_y (0 ?y ? 8) and Cu_1.8Mo₆S_8-y Te_y (0 ? y ?4) are reported. The data are examined for possible correlations with structural parameters of the rhombohedral unit call and the residual resistivity values. It is found that T_c decreases as the c/a ratio increases and as the rhombohedral angle approaches 90°. There is also an inverse correlation between T_c and the normal residual resistivity of the samples.     

Ag3PO4/BigFe4O9复合催化剂的制备及其光催化性能

利用水热法成功地制备得到具有高效光催化活性的Ag3PO4/Bi2Fe4O9复合型光催化剂.使用X-射线多晶粉末衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)对样品进行表征,并以罗丹明B为目标降解物对其光催化性能进行研究.结果表明:样品是由纳米Ag3 PO4颗粒负载在片状四边形的Bi2Fe4O9表面组成的,当Ag3PO4的负载量为4wt％时,复合材料的光催化效果最好,在可见光(波长＞420nm)照射下,1.5h内对100mL浓度为10-5mol.L-1罗丹明B溶液的脱色率可达98.7％.