Copper position in type-I Ba8Cu4Si42 clathrate

Local structure of Cu in a type-I Ba₈Cu₄Si₄₂ clathrate has been investigated by synchrotron X-ray powder diffraction, Cu K-edge extended X-ray absorption fine spectroscopy, X-ray absorption near edge spectroscopy (XANES) and theoretical calculation. It is found that XANES spectra cannot be explained by the substitution of Cu atoms at Si16i, and Si24k positions. Our calculations show that the binding energies of the Si atom in Si16i, Si24k and Si6c positions are 9.000, 9.495 and 8.911 eV, respectively. Both experimental and theoretical results support that Cu atoms in the type-I Ba₈Cu₄Si₄₂ clathrate, as a doped element, prefer to occupy the least-binding Si, i.e., the Si6c sites. No structural change between 112 and 300 K was observed and the (100)-faceted cubic crystal has negligible distortion/ordering according to transmission electron microscopy.     

偏压控制Cu2O和Cu在TiO2表面的生长及其光电化学性质

基于TiO₂/Ti 电极在含Cu²⁺溶液中的循环伏安图,调节电沉积的沉积电压,我们在TiO₂平整表面制备出Cu₂O和/或Cu颗粒. 通过扫描电镜（SEM）、X射线衍射（XRD）和X射线光电子能谱（XPS）表征,发现Cu₂O和Cu有不同的生长机制：Cu₂O颗粒在TiO₂表面分散结晶,而Cu颗粒是在已生长的颗粒上成核,从而形成堆积颗粒结构. 这是由于在Cu₂O/TiO₂界面和Cu/TiO₂界面形成不同的能带结构,使得电子的转移方式不同. 与纯TiO₂光阳极比较,可以观察到Cu₂O/TiO₂和Cu/TiO₂异质结构的光电流均有显著增强. 特别地,存在一个电压区间使得Cu₂O和Cu同时生长在TiO₂表面,此时对应的光电流比较稳定并且能达到最大. 紫外-可见（UV-Vis）漫反射光谱、电化学阻抗谱（EIS）和光电流-电压特性曲线均显示,Cu₂O和Cu明显有助于光的可见光吸收,同时Cu/TiO₂在光电转换过程中显示更宽波段的可见光利用率. 此外,开路电压的增加、有效的电荷分离和电极/电解质界面上载流子的快速迁移也增强了材料的光电化学性质.     

NO2对Cu/SAPO-34分子筛催化剂上NH3选择性催化还原NO性能的影响

主要考察了NO₂对Cu/SAPO-34 分子筛催化剂在整个温度范围内（100-500 ℃）NH₃选择性催化还原（SCR）NO性能的影响. 研究所使用样品为新鲜Cu/SAPO-34 催化剂在750 ℃下水热处理4 h 的稳定期样品.通过X射线衍射（XRD）和扫描电子显微镜（SEM）对样品的结构以及形貌进行表征,采用SCR活性评价、动力学实验以及原位漫反射傅里叶变换红外光谱（in situ-DRIFTS）表征催化剂的性能以及催化剂表面物种的变化. 活性评价实验结果表明,NO₂会抑制催化剂的低温（100-280 ℃）活性,但其存在会提高催化剂的高温（280 ℃以上）活性. 与此同时,随着反应物中NO/NO₂的摩尔比例减少,由于NH₄NO₃物种的分解,副产物（N₂2O）的浓度增大. 动力学结果表明,Cu/SAPO-34 催化剂上快速SCR反应的表观活化能（E_a=64.02 kJ·mol^-1）比标准SCR反应的表观活化能（E_a=48.00 kJ·mol^-1）更大. In situ-DRIFTS实验结果表明NO比NO₂更容易在催化剂表面形成硝酸盐,并且NO₂更容易与吸附在Brønsted 酸性位上的NH₃物种反应生成NH₄NO₃. 低温下,催化剂表面的NH₄NO₃物种会覆盖SCR反应的活性位,造成活性降低,但在高温时,形成的NH₄NO₃物种一部分会被NO还原为N2,而另一部分会直接热分解为N₂O,造成催化剂的选择性降低.     

Ln2BaZnO5 and Ln2BaZn1−xCuxO5: A series of zinc oxides with zinc in a pyramidal coordination

A series of zinc oxides Ln₂BaZnO₅ has been synthesized for Ln = Sm, Eu, Gd, Dy, Ho, and Y. Theses phases are orthorhombic and isostructural with the copper compounds Ln₂BaCuO₅ previously described, as shown from the structural study of one member Y₂BaZnO₅. In this structure, whose framework is built up from edge- and face-sharing LnO₇ polyhedra, the Zn²⁺ ions exhibit an unusual pyramidal coordination ZnO₅. The solid solution Y₂BaZn_1?xCu_xO₅ has been studied by infrared spectroscopy and electron spin resonance (ESR). The distorted square-based pyramidal configuration of Zn²⁺ and Cu²⁺ is confirmed. The ESR spectra of diluted samples exhibit a hyperfine structure and are typical of individual Cu(II) ions. For higher Cu(II) contents, they exhibit an anisotropic broad signal which is interpreted in terms of CuCu interactions.     

Synthesis,structure and magnetism of a one-dimensional silicotungstate array: K3H4Cu0.5{Cu[Cu7.5Si2W16O60(H2O)4(OH)4]2} · 9H2O

A structurally distinct, multi-copper(II)-substituted silicotungstate K₃H₄Cu_0.5{Cu[Cu_7.5Si₂W₁₆O₆₀(H₂O)₄(OH)₄]₂} · 9H₂O (1) has been synthesized and characterized by FT-IR spectroscopy, elemental analysis, variable-temperature magnetic measurements, electron spin resonance, and X-ray diffraction. Green crystalline plates of 1 were obtained by the reaction of K₈[γ-SiW₁₀O₃₆] · 12H₂O with 8 equiv. of Cu(II) in a 50% ethylene glycol solution. A cationic copper center connects the terminal oxygen atoms of neighboring polyanions, resulting in a one-dimensional structure. Magnetic susceptibility measurements indicate weak ferromagnetic superexchange between the Jahn–Teller-distorted S = 1/2 Cu(II) centers.     

Pd-Cu/γ-Al2O3催化苯乙炔选择性加氢反应

为了提高苯乙炔加氢反应中的苯乙烯选择性, 本文采用“胶体-等体积浸渍”两步法制备了Pd-Cu/γ-Al₂O₃双金属催化剂. 利用高分辨率透射电镜(HRTEM)、X射线光电子能谱(XPS)、CO脉冲化学吸附、N2物理吸附、电感耦合等离子体原子发射光谱(ICP-AES)等技术表征了Pd-Cu/γ-Al₂O₃的结构性质, 考察了Cu/Pd 摩尔比、Pd负载量以及金属引入顺序对Pd-Cu/γ-Al₂O₃催化苯乙炔选择性加氢性能的影响. 结果表明, 与Pd/γ-Al₂O₃单金属催化剂相比, Pd-Cu/γ-Al₂O₃的苯乙烯选择性大幅度提高, 尤其是当Pd负载量为0.3%(w), 且Cu/Pd摩尔比为0.6时, Pd-Cu/γ-Al₂O₃表现出优异的加氢选择性; 在0.1 MPa和40 ℃下, 当苯乙炔转化率为90%时, 双金属催化剂的苯乙烯选择性可达95%; 当转化率达到99%以上时, 苯乙烯选择性仍保持在82%左右. 分析表明, Pd-Cu/γ-Al₂O₃中形成了Pd-Cu合金, 但是两种金属间不存在电子转移, Cu对Pd的几何效应才是导致Pd-Cu/γ-Al₂O₃苯乙烯选择性增加的主要原因.     

14N Nuclear quadrupole interaction in Cu(II) doped l-alanine

The ¹⁴N nuclear quadrupole interaction tensor P_N measured by ENDOR in Cu(II) doped l-alanine is analyzed in terms of the Townes and Dailey theory assuming a tetrahedrally bonded N atom. The results of this analysis are compared with those for the ¹⁴N in pure l-alanine and it is found that the principal directions of the P_N tensor are drastically changed upon metal complexation as a consequence of the higher electron affinity of Cu(II) with respect to C and H. Comparison of the corresponding bond populations in pure and Cu(II) doped l-alanine indicates that the Cu draws 0.11 more electron from the N than the substituted H atom.     

Li4Ti5O12/(Cu+C)复合材料的制备及电化学性能

以Li₄Ti₅O₁₂,Cu(CH₃COO)₂·H₂O和C₆H₁₂O₆为前驱体,化学沉积与热分解结合合成锂离子电池负极材料Li₄Ti₅O₁₂/(Cu+C)。采用X-射线衍射(XRD)、扫描电子显微镜(SEM)、恒流充放电、循环伏安和电化学阻抗方法表征样品的结构、形貌和电化学性能。结果表明,Li₄Ti₅O₁₂表面包覆的Cu与C提高了Li₄Ti₅O₁₂电极材料的导电率,其循环性能和倍率性能得到有效地改善。在0.5C、1C和3C倍率下,经过50次充放电循环,放电比容量分别为168.2、160、140.6 mAh·g^-1,其容量保持率分别为88.7%、84.4%、71.2%。电化学阻抗测试表明,表面包覆的Cu与C使其电荷转移阻抗大幅度减少。     

Crystal structure, magnetic properties and conductivity of CuSbTeO3Cl2

CuSbTeO₃Cl₂ has been isolated during an investigation of the system Cu₂O:TeCl₄:Sb₂O₃:TeO₂. The new compound is light yellow and crystallises in the monoclinic system, space group C2/m, a=20.333(5) Å, b=4.0667(9) Å, c=10.778(2) Å, Z=6. The structure is layered and is built up from corner and edge sharing [(Sb,Te)O₄E] trigonal bipyramids that have the lone pair (E) directed towards one of the equatorial positions, those groups build up [(Sb,Te)₂O₃E₂⁺]_n layers. The copper and the chlorine atoms are located in between those layers. There are two different Cu positions. The [Cu1Cl₄] group is a slightly distorted tetrahedron and these tetrahedra make up chains by corner sharing. The electron density for the half occupied Cu2 atom is spread out in the structure like a worm that run along the b-axis in the space in between two chains of [Cu1Cl₄] tetrahedrons. Analysis of the diamagnetic response in magnetic susceptibility measurements is in perfect agreement with a Cu⁺ valence. Conductivity measurements in the temperature range 355–590 K gives an activation energy of 0.55 eV. The delocalised Cu2 position in the structure suggests that the compound is a Cu⁺ ionic conductor along the b-axis.     

Effect of ligands on the thermolysis of the double complexes [Co(NH3)6]2C2O4[Cu(C2O4)2]2 and [Co(NH3)6]Cl[Cu(C7H4O3)2]

The thermolysis of the complexes [Co(NH₃)₆]₂C₂O₄[Cu(C₂O₄)₂]₂ (I) and [Co(NH₃)₆]Cl[Cu(C₇H₄O₃)₂] (II) in air and hydrogen at 200, 350, and 500°C and the composition and properties of the thermolysis products are considered. The oxidative thermolysis of the complexes yields mixtures of cobalt and copper oxides, including mixed ones. The reductive thermolysis of the complexes yields a Co + Cu bimetallic powder in the case of compound I and a Co + Cu + C powder in the case of compound II. The thermal behavior of the complexes is governed by the nature of the ligand coordinated to the copper atom. The observed data are explicable in terms of the properties of this ligand. The chemistry of the oxidative and reductive thermolysis is discussed. Original Russian Text ? D.P. Domonov, S.I. Pechenyuk, N.L. Mikhailova, A.T. Belyaevskii, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 7, pp. 1104–1110.     

Laser-induced fluorescence measurement of the nascent rotational distribution of N+2 (X2Σ+g) formed by electron impact on N2

The internal state distribution of ground state N⁺₂ ions formed from N₂ by electron impact ionization is measured under collision-free conditions using laser-induced fluorescence. Analysis of the B–X (0, 0) band shows the rotational distribution to be characterized by a temperature which increases slightly with decreasing electron energy (60–100 eV). Cascade contributions are unimportant.     

Oxidation‐induced nanostructures on Cu{100}, Cu(Ag) and Ag/Cu{100} studied by photoelectron spectroscopy

Initial surface oxidation and nanoscale morphology on Cu{100}, Cu(Ag) and Ag/Cu{100} have been investigated in situ by X‐ray photoelectron spectroscopy (XPS), X‐ray induced Auger electron spectroscopy (XAES) and the inelastic electron background analysis as a function of oxygen exposure at 3.7 × 10^?2 and 213 mbar pressures at a surface temperature of 373 K. Relative Cu₂O concentrations have been quantified by analysis of the peak shape of the XAES Cu LMM transition. The surface morphology of Cu₂O islands and the Ag layer has been characterized by inelastic electron background analysis of XAES O KLL and Ag 3d transitions. Oxygen‐induced segregation of Cu, as well as the subsequent Cu₂O island formation on Cu(Ag) and Ag/Cu{100} surfaces, has been investigated quantitatively. Our results indicate that Ag has a clear inhibitive effect on the initial oxidation and Cu₂O island formation on Cu(Ag) and Ag/Cu{100} surfaces. The Cu₂O islands are also observed to remain highly strained on Ag/Cu{100} even at higher O₂ exposures. The results suggest that strained Cu₂O islands eventually penetrate through the buried Ag layer, and in conjunction with segregating Cu atoms enable the oxidation to proceed at a similar rate to or even faster than on the unalloyed Cu surface. Copyright © 2007 John Wiley & Sons, Ltd.     

Structural and magnetic properties of nanocrystalline Ni1−xCuxFe2O4 prepared through oxalates precursors

Spinel ferrites of the composition Ni_1−xCu_xFe₂O₄ (x = 0.0-1.0) have been prepared through the thermal decomposition of their respective impregnated oxalates. The oxalate decomposition process was followed using differential thermal analysis-thermogravimetry techniques (DTA-TG). The synthesized nanocrystallites were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). The formation of single-phase ferrite is confirmed by XRD. Tetragonal deformation is observed for samples with composition x ? 0.7. The increase in the lattice parameter with increasing Cu content can be explained based on the relative ionic radius. The TEM image shows spherically non-agglomerated particles with an average crystallite size that agrees well with that obtained from XRD. FT-IR studies show two absorption bands (ν₁ and ν₂) near to 600 and 400 cm⁻¹ for the tetrahedral and octahedral sites, respectively. The hysteresis measurements were done using a vibrating sample magnetometer (VSM). The cation distribution in these compositions is calculated from the magnetization data. With increasing Cu content, the saturation magnetization (M_s) was observed to decrease while the coercivity (H_c) increases. The possible reasons responsible for the composition dependence of the magnetic properties were discussed. The Curie temperature, measured through the temperature dependence of the dc-molar magnetic susceptibility, was found to decrease with increasing Cu content.     

CdS插层的K4Nb6-xCuxO17复合物的制备及其光催化制氢活性

以Nb2O5,K2CO3和CuO为原料经高温固相反应合成K4Nb6-xCuxO17催化剂,并通过层间离子交换反应,胺插入反应以及硫化反应制备CdS插层K4Nb6-xCuxO17复合催化剂(K4Nb6-xCuxO17/CdS)。利用X射线衍射(XRD),X射线光电子能谱(XPS),场发射扫描电镜(SEM),X射线能谱仪(EDX),紫外-可见漫反射(UV-Vis),分子荧光光谱(PL)等技术对催化剂进行表征。考察了催化剂的可见光催化制氢活性。结果表明,Cu离子掺杂进入K4Nb6O17晶格中,CdS位于K4Nb6O17层间。CdS插层K4Nb6-xCuxO17催化剂的最大吸收光波长约为550 nm。催化剂制氢活性有明显提高,紫外光和可见光下3 h产氢量分别达到279.83 mmol.gcat-1和7.11 mmol.gcat-1。最后讨论了复合催化剂光生电荷转移机理。     

First-principles study of O2 adsorption and dissociation on the CuCr2O4 (100) surface

The adsorption and dissociation of molecular oxygen on spinel CuCr₂O₄ (100) surface were carried out by first-principles calculations based on density functional theory (DFT). The calculated results indicate that the Cr site is most favorable for atomic oxygen adsorption, with an adsorption energy of 402.8 kJ/mol. For molecular oxygen adsorption, there are three types of favorable interaction modes: O₂ forms bonds with the Cu site or O₂ binds to two Cr sites or O₂ interacts with both Cu and Cr sites simultaneously. The lowest activation energy (E_a = 35.4 kJ/mol) was found through exploring possible reaction pathways for O₂ dissociation. The relationship between E_a and reaction enthalpy (ΔH) for O₂ dissociation adsorption reactions fits Brønsted-Evans-Polanyi (BEP) behavior.     

Specific heat measurements on the magnetic layer compounds(BA)2Cu(Ox)2 and (CHA)2Cu(Ox)2·H2O

Specific heat data on (BA)₂Cu(Ox)₂ and (CHA)₂Cu(Ox)₂·H₂O below 1 K are reported (BA = C₆H₅ CH₂NH₃⁺, CHA = C₆H₃⁺, Ox = C₂O₄²). The magnetic contributions have the form of broad maxima, occurring near 0.15. A λ-type anomaly is observed for (BA)₂Cu(Ox)₂ at T_c = 0.116(3) K. For (CHA)₂Cu(Ox)₂·H₂O no such ordering is seen.(BA)₂Cu(Ox)₂ appears to be a quadratic S = 1/2 Heisenberg antiferromagnet with J/k = ?0.145 (3) K. The compound (CHA)₂Cu(Ox)₂·H₂O shows a behaviour that is in between 1-D and 2-D S = 1/2 Heisenberg antiferromagnetism.     

Evolution and characterization of fluorite-like nano-SrBi2Nb2O9 phase in the SrO-Bi2O3-Nb2O5-Li2B4O7 glass system

Transparent glasses of various compositions in the system (100−x)Li₂B₄O₇−x(SrO-Bi₂O₃-Nb₂O₅) (where x=10, 20, 30, 40, 50 and 60, in molar ratio) were fabricated via splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses. X-ray powder diffraction (XRD) and transmission electron microscopic studies confirmed the amorphous nature of the as-quenched and crystallinity in the heat-treated samples. Fluorite phase formation prior to the perovskite SrBi₂Nb₂O₉ phase was analyzed by both the XRD and high-resolution transmission electron microscopy. Dielectric and the optical properties (transmission, optical band gap and Urbach energy) of these samples have been found to be compositional dependent. Refractive index was measured and compared with the values predicted by Wemple-Didomemenico and Gladstone-Dale relations. The glass nanocomposites comprising nanometer-sized crystallites of fluorite phase were found to be nonlinear optic active.     

Local structure of Cu in Cs8Na16Cu5Ge131 type II clathrate

We have used X-ray absorption spectroscopy (XAS) to investigate the local structure of Cu and Ge in the Cs₈Na₁₆Cu₅Ge₁₃₁ type II clathrate. We show that the local structure parameters for Ge (coordination number and distances) are consistent with those derived on the basis of XRD investigation of Cs₈Na₁₆Ge₁₃₆. The EXAFS data suggest that Cu either randomly substitutes for Ge on the clathrate framework or preferentially on the 96g site but not preferentially on the 32e or 8a sites (Wyckoff notation). Furthermore, we find that the Cu-Ge distance is smaller than the Ge-Ge distance by 0.13 Å, indicating a local distortion around the Cu atoms. The estimated degrees of disorder for Cu-Ge and Ge-Ge interactions indicate the Cu-Ge clathrate framework to be relatively stiff, while those for Na-Ge and Cs-Ge interactions corroborate previous observations of strong thermal disorder of the alkali guests in these materials. Our XAS results offer insight into the site substitution of Cu in this material, information unattainable from X-ray diffraction due to the lack of scattering contrast between Cu and Ge.     

Crystal and electronic structures of CaAl2Si2-type rare-earth copper zinc phosphides RECuZnP2 (RE=Pr, Nd, Gd-Tm, Lu)

The quaternary rare-earth phosphides RECuZnP₂ (RE=Pr, Nd, Gd-Tm, Lu) have been prepared by reaction of the elements at 900 °C, completing this versatile series which forms for nearly all RE metals. They adopt the trigonal CaAl₂Si₂-type structure (Pearson symbol hP5, space group P3?m1, Z=1), as confirmed by single-crystal X-ray diffraction analysis on ErCuZnP₂ and powder X-ray diffraction analysis on the remaining members. The Cu and Zn atoms are assumed to be disordered over the single transition-metal site. Band structure calculations on a hypothetically ordered YCuZnP₂ model suggest a semimetal, with a zero band gap between the valence and conduction bands. This electronic structure is supported by XPS valence band spectra for RECuZnP₂ (RE=Gd-Er), in which the intensity drops off smoothly at the Fermi edge. The absence of a band gap permits the electron count to deviate from the precise value of 16 e⁻ per formula unit, as demonstrated by the formation of a solid solution in GdCu_xZn_2−xP₂ (1.0≤x≤1.3), while still retaining the CaAl₂Si₂-type structure. Because the Cu 2p XPS spectra indicate that the Cu atoms are always monovalent, the substitution of Cu for Zn leads to a decrease in electron count and a lowering of the Fermi level in the valence band. The magnetic susceptibility of RECuZnP₂ (RE=Gd-Er), which obeys the Curie-Weiss law, confirms the presence of trivalent RE atoms.     

Characterization of quasi-one-dimensional S=1/2 Heisenberg antiferromagnets Sr2Cu(PO4)2 and Ba2Cu(PO4)2 with magnetic susceptibility, specific heat, and thermal analysis

Properties of Sr₂Cu(PO₄)₂ and Ba₂Cu(PO₄)₂ having [Cu(PO₄)₂]_∞ linear chains in their structures with Cu-O-P-O-Cu linkages were studied by magnetic susceptibility (T=2-400 K, H=100 Oe) and specific heat measurements (T=0.45-21 K). Magnetic susceptibility versus temperature curves, χ(T), showed broad maxima at T_M=92 K for Sr₂Cu(PO₄)₂ and T_M=82 K for Ba₂Cu(PO₄)₂ characteristic of quasi-one-dimensional systems. The χ(T) data were excellently fitted by the spin susceptibility curve for the uniform S=1/2 chain (plus temperature-independent and Curie-Weiss terms) with g=2.153(4) and J/k_B=143.6(2) K for Sr₂Cu(PO₄)₂ and g=2.073(4) and J/k_B=132.16(9) K for Ba₂Cu(PO₄)₂ (Hamiltonian H=JΣS_iS_i+1). The similar J/k_B values were obtained from the specific heat data. No anomaly was observed on the specific heat from 0.45 to 21 K for both compounds indicating that the temperatures of long-range magnetic ordering, T_N, were below 0.45 K. Sr₂Cu(PO₄)₂ and Ba₂Cu(PO₄)₂ are an excellent physical realization of the S=1/2 linear chain Heisenberg antiferromagnet with k_BT_N/J<0.34% together with Sr₂CuO₃ (k_BT_N/J≈0.25%) and γ-LiV₂O₅ (k_BT_N/J<0.16%). Sr₂Cu(PO₄)₂ and Ba₂Cu(PO₄)₂ were stable in air up to 1280 and 1150 K, respectively.