A novel preparation process for LaCuO3 involving a high pressure oxidation of precursor derived from the perovskite structure: An appropriate route for doping with 57Fe Mössbauer probe

In order to dope LaCuO₃ by ⁵⁷Fe Mössbauer probe, a novel high pressure oxidation process was developed. The orthorhombic phase La₂Cu₂O₅:⁵⁷Fe (2%) was used as a precursor due to its structure derived from the perovskite.The role of the structure of the precursor has been underlined through a comparison of the reaction routes from both structural forms (monoclinic and orthorhombic) of La₂Cu₂O₅.This example illustrates the key role by the composition and the structure of the precursor for preparing novel materials.     

Anodic synthesis and XPS analysis of La_(1-x)Na_xCu_2O_4

The single phase La1-x NaxCu2O4 crystals were synthesized by an electrochemical method from molten KOH/NaOH/KNO3 at 280-300℃ while La2-yNayCuO4 were prepared by precipitation from the same molten salt. The resulting crystals were characterized by using SEM, XRD, EDX and XPS. XPS analysis revealed that the La3d satellite structures of La1-xNaxCu2O4 were quite different from those of La2-yNayCuO4. These differences have been attributed to the changes in crystal structures, bond lengths and covalent character of the metal-ligand bonds.     

The hunt for LaFeSbO: Synthesis of La2SbO2 and a case of mistaken identity

The phase La₂SbO₂ has been identified and characterized in the course of our efforts to realize LaFeSbO, a composition of great interest to the superconductor community. The compound La₂SbO₂ is a tetragonal layered oxypnictide containing La₂O₂ layers similar to LaMPnO compositions (where M=transition metal, Pn=pnictide) separated by pnictide anion layers. In order to better understand why LaFeSbO has remained elusive, density functional theory calculations have been used to determine the ground state heats of formation for LaFeSbO, La₂SbO₂, and other competing phases within the La–Fe–Sb–O system, as well as the phonon spectrum for LaFeSbO. These efforts suggest that LaFeSbO is a potentially metastable composition.     

Formation of the Compound La2BaCuO5 (La4Ba2Cu2O10)

Synthesis of the compound La₂BaCuO₅ (La₄Ba₂Cu₂O_{1 0}), whose X-ray diffraction pattern is identical to that available in the literature for the solid solution La_3.6Ba_2.4Cu_1.8O_9.6, was studied.     

Preparation of trimetallic electrocatalysts by one-step co-electrodeposition and efficient CO2 reduction to ethylene

Use of multi-metallic catalysts to enhance reactions is an interesting research area, which has attracted much attention. In this work, we carried out the first work to prepare trimetallic electrocatalysts by a one-step co-electrodeposition process. A series of Cu–X–Y (X and Y denote different metals) catalysts were fabricated using this method. It was found that Cu₁₀La₁Cs₁ (the content ratio of Cu²⁺, La³⁺, and Cs⁺ in the electrolyte is 10 : 1 : 1 in the deposition process), which had an elemental composition of Cu₁₀La_0.16Cs_0.14 in the catalyst, formed a composite structure on three dimensional (3D) carbon paper (CP), which showed outstanding performance for CO₂ electroreduction reaction (CO₂RR) to produce ethylene (C₂H₄). The faradaic efficiency (FE) of C₂H₄ could reach 56.9% with a current density of 37.4 mA cm⁻² in an H-type cell, and the partial current density of C₂H₄ was among the highest ones up to date, including those over the catalysts consisting of Cu and noble metals. Moreover, the FE of C₂₊ products (C₂H₄, ethanol, and propanol) over the Cu₁₀La₁Cs₁ catalyst in a flow cell reached 70.5% with a high current density of 486 mA cm⁻². Experimental and theoretical studies suggested that the doping of La and Cs into Cu could efficiently enhance the reaction efficiency via a combination of different effects, such as defects, change of electronic structure, and enhanced charge transfer rate. This work provides a simple method to prepare multi-metallic catalysts and demonstrates a successful example for highly efficient CO₂RR using non-noble metals.

Trimetallic Cu₁₀La₁Cs₁ catalysts prepared via a one-step co-electrodeposition strategy can act as a robust electrocatalyst for CO₂RR to C₂H₄.     

On the role of anion templates for the self-assembly of octanuclear copper(I) dichalcogenophosph(in)ate clusters

The octanuclear Cu^I cubic clusters [Cu₈(S₂PPh₂)₆]²⁺ (1) and [Cu₈(μ₈-Cl)(S₂PPh₂)₆]⁺ (2) have been prepared and crystallographically characterized, and their cluster bonding modes investigated with density functional theory (DFT) calculations. Both are rare examples of metal dithiophosphinate clusters and 1 is the first example of a non anion-centered or ‘empty’ dithiophosph(in)ate Cu^I₈ cube. DFT calculations indicate that the stability of the empty cluster 1 can be attributed to its strong metal–ligand interactions, with no significant Cu?Cu bonding interactions present. Comparison of the solid-state structures of 1, 2 and the analogous sulfide centered cluster [Cu₈(μ₈-S)(S₂PPh₂)₆] (3) reveals a significant contraction of the octanuclear Cu^I₈ cube upon anion encapsulation. This contraction is shown, using DFT calculations, to be predominately assignable to the ionic interaction between the Cu^I cations and the encapsulated anion center.     

中温固体氧化物燃料电池La1.6Sr0.4Ni1-xCuxO4阴极材料的制备及电化学性能

采用甘氨酸-硝酸盐法合成了中温固体氧化物燃料电池阴极材料La_1.6Sr_0.4Ni_1-xCu_xO₄ (x=0.2, 0.4, 0.6,0.8), 利用X射线衍射(XRD)和扫描电子显微镜(SEM)对其结构和微观形貌进行了表征. 结果表明, 该阴极材料与固体电解质Ce_0.9Gd_0.1O_1.95(CGO)在1000 °C烧结时不发生化学反应, 且烧结4 h 后, 二者之间可形成良好的接触界面. 利用电化学交流阻抗谱技术对阴极材料的电化学性能进行研究, 结果显示, 当Cu离子掺杂量(x)为0.6 时, La_1.6Sr_0.4Ni_0.4Cu_0.6O₄阴极具有最小的极化电阻, 在空气中当测试温度为750 °C时, 极化电阻为0.35 Ω·cm². 在不同氧分压条件下电化学阻抗谱分析结果表明, 电极上的两个氧还原反应主要包含氧离子从三相界面向电解质CGO 转移的过程和电荷的迁移过程, 其中电荷的迁移过程为电极反应的速率控制步骤.La_1.6Sr_0.4Ni_0.4Cu_0.6O₄电极在空气中700 °C和阴极电流密度为45 mA·cm^-2时, 阴极过电位为45 mV. 本研究的初步结果表明La_1.6Sr_0.4Ni_1-xCu_xO₄材料是一种电化学性能较为优良的新型中温固体氧化物燃料电池(IT-SOFC)阴极材料.     

The synthesis and transport properties of the cuprates La<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript>1 + <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>2</Subscript>O<Subscript>6 + δ</Subscript>

The cuprates La_{2 ? x} Sr_{1 + x} Cu₂O_{6 + δ}(x = 0, 0.1, 0.2) are synthesized by solid-state method. Their dc conductivity was studied over the 373 to 1173 K temperature range and 10 to 2.1 × 10⁴ Pa oxygen partial pressure range by using four-probe technique. It is shown that the cuprate conductivity in air is maximal at ～673 K; it is 60 S/cm for La₂SrCu₂O_6.09; 68 S/cm, for La_1.9Sr_1.1Cu₂O_6.18; and 81 S/cm, for La_1.8Sr_1.2Cu₂O_6.10. The thermal expansion coefficient of La₂SrCu₂O_6.09 is determined by thermomechanical method and high-temperature X-ray diffraction method; its value (16 ppm K^?1) shows that the material is compatible with the ceria-based solid electrolytes during the thermal cycling.     

Reactions between YBa2Cu3O7−δ and La2O3 and SrCO3

Solid state reactions at 925°C between the high-T _c ceramic superconductor YBa₂Cu₃O_7?δ and La₂O₃ and SrCO₃, respectively, mixed in various molar ratiosr=MeO_n/YBa₂Cu₃O_7?δ, were studied using X-ray powder diffraction and scanning electron microscopy. The reaction between YBa₂Cu₃O_7?δ and La₂O₃ yielded (La_1?xBa_x)₂CuO_4?δ, withx≈0.075?0.10. La_2?xBa_1+xCu₂O_6?δ, withx≈0.2?0.25 and La-doped (Y_1?xLa_x)₂BaCuO₅, withx≈0.10?0.15. Forr=3.0, Y-doped La₂BaCuO₅ resulted also. The reaction between YBa₂Cu₃O_7?δ and SrCO₃ yielded (Sr_1?zBa_z)₂CuO₃, withz≈0.1, Y₂(Ba_1?zSr_z)CuO₅, withz=0.1?0.15, and a nonsuperconducting compound with an approximate composition of Y(Ba_0.5Sr_0.5)₅Cu_3.5O_10±δ. At values ofr≤2.0, unsubstituted YBa₂Cu₃O_7?delta was found in the reaction products.     

Synthesis, crystal structure and magnetic properties of the spin ladder compounds La2(Cu1−xZnx)2O5 and La8(Cu1−xZnx)7O19

The influence of Zn-doping on the crystal structure and magnetic properties of the spin ladder compounds La₂Cu₂O₅ (4-leg) and La₈Cu₇O₁₉ (5-leg) have been investigated. The La₂(Cu_1−xZn_x)₂O₅ and La₈(Cu_1−xZn_x)₇O₁₉ solid solutions were obtained as single phases with x=0-0.1 via the solid-state reaction method in the temperature range between 1005-1010 °C and 1015-1030 °C in oxygen and air atmospheres, respectively. The lattice parameters a and c of the monoclinic crystal structures as well as the unit cell volume V increase with increasing x, while b and β decrease for both series. The magnetic susceptibilities χ of both series show a very similar behavior on temperature as well as on Zn-doping, which is supposed to be due to the similar Cu-O coordination in both La₂Cu₂O₅ and La₈Cu₇O₁₉. For low Zn-doping (x?0.04), a spin-chain like behavior is found. This quasi-one-dimensional behavior is strongly suppressed in both series for x?0.04. Here, the maximum (characteristic for spin chains) in χ(T) disappears and χ(T) decreases monotonically with increasing temperature.     

Synthesis, crystal and electronic structure, and physical properties of the new lanthanum copper telluride La3Cu5Te7

The new lanthanum copper telluride La₃Cu_5−xTe₇ has been obtained by annealing the elements at 1073 K. Single-crystal X-ray diffraction studies revealed that the title compound crystallizes in a new structure type, space group Pnma (no. 62) with lattice dimensions of a=8.2326(3) Å, b=25.9466(9) Å, c=7.3402(3) Å, V=1567.9(1) Å³, Z=4 for La₃Cu_4.86(4)Te₇. The structure of La₃Cu_5−xTe₇ is remarkably complex. The Cu and Te atoms build up a three-dimensional covalent network. The coordination polyhedra include trigonal LaTe₆ prisms, capped trigonal LaTe₇ prisms, CuTe₄ tetrahedra, and CuTe₃ pyramids. All Cu sites exhibit deficiencies of various extents. Electrical property measurements on a sintered pellet of La₃Cu_4.86Te₇ indicate that it is a p-type semiconductor in accordance with the electronic structure calculations.     

Phase of the composition CaBaLaCu2FeO7.5: Synthesis, structure, M?sbauer spectra

The phase of the composition CaBaLaCu₂FeO_7.5 is synthesized from the previously obtained CaCuO₂, La₂Cu₂O₅, and BaFeO₂ double oxides enriched up to 14.7% in ⁵⁷Fe. The phase has the orthorhombic crystal system with the unit cell parameters as follows: a = 0.3882(3) nm, b = 0.3911(3) nm, c = 1.1823(8) nm. Based on the M?sbauer spectra analysis, the conclusion is drawn that iron atoms occupy only Cu(1) sites in the lattice, while more than 90% of them are in the Fe⁴⁺ valence state (80% of these atoms have the tetragonal pyramidal coordination).     

Influence of60Co gamma radiation on La2CuO4 catalyst for the decomposition of hydrogen peroxide

The catalytic activity of La₂CuO₄ for the decomposition of H₂O₂ was studied in detail. La₂CuO₄ was prepared by the ceramic method in four different ways. Gamma irradiation of the La₂CuO₄ samples increased their catalytic activity irrespective of the method of preparation. The enhanced catalytic activity is attributed to irradiation generated Cu⁺ centres on the surface of the catalyst.     

Crystal Structure Investigations and Thermal Behavior of the Five‐Leg Spin Ladder Compound La8Cu7O19

La₈Cu₇O₁₉ was synthesized by solid state reaction of the oxides La₂O₃ and CuO at 1288 K in air. The crystal structure was determined by a joint Rietveld refinement of X‐ray and neutron powder diffraction data. La₈Cu₇O₁₉ crystallizes in the monoclinic space group C2/c (No. 15) with the lattice parameters a = 13.8310(4)Å, b = 3.75827(9)Å, c = 34.5917(8)Å and β = 99.332(2)°. La₈Cu₇O₁₉ is the n = 3 member of the homologous series La_4+4nCu_8+2nO_14+8n. The Cu—O sub‐structure in La₈Cu₇O₁₉ contains infinite ribbons, which can be described as perovskite type layers with a width of n = 3 Jahn‐Teller‐elongated octahedra, and Cu—O planes of complex geometry. DSC/TG‐measurements in different gas atmospheres show peritectic decomposition of La₈Cu₇O₁₉. The anisotropic thermal expansion of the lattice parameters was investigated using synchrotron radiation. The Madelung part of lattice energy was calculated and compared with the corresponding values of other lanthanum cuprates.     

Chemical stability of La1−xSrxCrO3 in oxidizing atmospheres

The single-phase region of La_1−xSr_xCrO₃ (x=0.1, 0.2, 0.3) was precisely determined as a function of temperature, P_O2 and Sr content. The powders with the nominal composition of La_1−xSr_xCrO₃ were equilibrated under various conditions, and then identified by XRD analyses. To confirm the equilibration, two independent experiments were performed for each composition observing (i) the precipitation of the second phase from a single-phase solid solution, and (ii) the formation of the single phase from the constituent oxides. Two kinds of second phases, SrCrO₄ and an unknown phase, were observed depending on the conditions. The second phases tended to appear at low temperature, in high P_O2 and with a large Sr content. The single-phase regions obtained via the two equilibration routes were in good agreement with each other. The thermodynamic calculations on the supposition of ideality of the solid solution essentially reproduced the experimental results. When this material is used as the interconnects of solid oxide fuel cells, much attention should be paid to its relatively narrow solubility range of Sr; for example, the solubility limit is approximately 0.1 under a typical cathode-side condition (1273 K, air).     

Oxidation of styrene and cyclohexene with TBHP catalyzed by copper(II) complex encapsulated in zeolite-Y

Reaction of monobasic tridentate Hacpy-oap (Hacpy-oap?=?Schiff base derived from 2-acetylpyridine and o-aminophenol) with Cu^IICl₂ in refluxing methanol results in formation of [Cu^II(acpy-oap)Cl]. DFT calculations have been used to optimize structure of the complex. [Cu^II(acpy-oap)Cl] has also been encapsulated in the nanocavity of zeolite-Y and its encapsulation ensured by various physico-chemical techniques. Neat as well as encapsulated complexes are active catalysts for oxidation of styrene and cyclohexene using tert-butylhydroperoxide. Reaction conditions for oxidation of these substrates have been optimized by concentration of oxidant, amount of catalyst, volume of solvent and temperature of the reaction mixture. [Cu^II(acpy-oap)Cl] does not leach metal ion during catalytic activity and is recyclable.     

Étude structurale de britholite au césium Sr7La2Cs(PO4)5(SiO4)F2

Several studies demonstrated the ability of britholites to retain radionuclides such as the caesium and actinides. Therefore, three compounds with formulas Sr₈LaCs(PO₄)₆F₂, Sr₇La₂Cs(PO₄)₅(SiO₄)F₂ and Sr₂La₇Cs(SiO₄)₆F₂, were prepared by solid state reaction. However, it seems that only the mono-silicated composition was obtained in a pure state. In this present work, the X-ray diffraction and magnetic nuclear resonance have been used to investigate the structure for this composition. The results showed that in fact this phase was not pure, but it was mixed with a secondary phase, SrLaCs(PO₄)₂. The refinement by the Rietveld method allowed also to precise the distribution of La³⁺ and Cs⁺ ions between the two cationic sites of the apatite.     

Subsolidus phase equilibrium in the Cu-Sb-O system

T6he study of the subsolidus phase equilibrium in Cu-Sb-O system was started using samples with compositions laying, at room temperature, in the CuO-Sb₂O₃ subsystem. Isothermal and non-isothermal experiments were performed to analyze the system in the 500–1000°C range. At high temperatures (over 500°C) the system transforms in a quaternary one: CuO-Cu₂O-Sb₂O₃-Sb₂O₅ as Sb₂O₃ undergoes oxidation to Sb₂O₄ and Sb₂O₅ and Cu₂O₃ reduces to Cu₂O. The formation of the CuSb₂O₆ and Cu₄SbO_4.5 binary compounds is reported. The calculations of mass variation and atomic composition modifications lead to a quaternary oxide representation of the subsolidus phase equilibrium.     

Applications of the model potential method to transition metal compounds

Model potential parameters and basis sets, presented previously for the transition metal atoms Sc through Hg, are tested in calculations of the transition metal compounds (CuF, CuCl, Cu₂, TiCl₄, ZrCl₄, CoF₆^3?, CoF₆^2?, AgH, AuH, CrF₆, ScO, ZrO, Cr₂, Mo₂). Calculated values of the bond distances, vibrational frequencies, and some transition energies (for Cu₂ and CoF₆^2?) are compared with those given by all-electron calculations with basis sets of high quality. Singlet-triplet splittings in Cu₂ and correlation energies in CrF₆^n? (n = 0, 1, and 2) are also examined. The satisfactory results obtained by these calculations strongly support the contention that the model potential method is a reliable and economical alternative to the ab initio Hartree-Fock-Roothaan method.     

Kinetic study on thermal decomposition of the high-temperature superconductor in vacuum microbalance

In this paper the theoretical approach and applications of Cahn ultramicrobalance to kinetic study on the thermal decomposition of the high-temperature Y₁Ba₂Cu₃O_7-x superconductor are presented. Thermogravimetric in situ measurements of oxygen loss from Y₁Ba₂Cu₃O₆ samples heated isothermally in a relatively high dynamic vacuum were performed with a Cahn RG electrobalance. Single-phase orthorhombic samples of composition Y₁Ba₂Cu₃O_7-x (highest oxygen content) were synthesized from stoichiometric (1:2:3) mixtures of high-purity Y₂O₃, BaCO₃ and CuO. The original 1:2:3 mixture was prepared by the two-stage procedure described earlier. The crystal structure of the sample in the original orthorhombic phase was controlled by the X-ray powder method (CuK_α radiation) using a Stadi P Stoe diffractometer with a position-sensitive detector. Activation energy is estimated from appropriate Arrhenius plots. This revised version was published online in July 2006 with corrections to the Cover Date.