Interface structure and misfit relaxation in YBa2Cu3O7‐δ/PrBa2Cu3O7‐δ heterostructures on SrTiO3(001) substrates

Structural properties of YBa₂Cu₃O_7‐δ/PrBa₂Cu₃O_7‐δ heterointerfaces have been investigated by aberration‐corrected electron microscopy. Experimental evidence shows that c‐axis‐oriented YBa₂Cu₃O_7‐δ/PrBa₂Cu₃O_7‐δ heterostructures with atomically sharp interface epitaxially grow on SrTiO₃(001) substrates. In terms of the contrast analysis, no apparent interdiffusion between YBa₂Cu₃O_7‐δ and PrBa₂Cu₃O_7‐δ occurs at the interface. In addition, stand‐off misfit dislocations and planar faults appear within PrBa₂Cu₃O_7‐δ layer near the interface. Both misfit dislocations and interfacial dislocations resulting from the termination of planar faults contribute to misfit relaxation at the YBa₂Cu₃O_7‐δ/PrBa₂Cu₃O_7‐δ interface. The defect configuration of planar faults and stand‐off misfit dislocations is explored. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis,composition, and magnetic properties of the ferrimagnetic NdCu3−xMn4+xO12 perovskite-like phases

A magnetic oxide with composition close of NdCu₃Mn₄O₁₂ with a perovskite-related cubic structure ($\text{a ? 7.30}$ Å, space group Im3, Z = 2) has been synthesized by using either the high-pressure or the hydrothermal technique. The composition is strongly dependent on the synthesis conditions. A partial reduction of Mn⁴⁺ in the octahedral sites, resulting in a partial substitution of Cu²⁺ by Mn³⁺ in the Jahn-Teller sites, leads to the actual formula Nd(Cu²⁺_3?xMn³⁺_x)(Mn⁴⁺_3?xMn³⁺_1+x)O₁₂. For the compound synthesized at 650°C/2 kbar, the value of the substitution parameter x, as determined by neutron diffraction, is 0.32. For samples synthesized at higher temperatures, larger values of x are obtained. The compound is ferrimagnetic with Néel temperature of 390 K and a spontaneous magnetization of 93 emu/g at 4 K (52 emu/g at room temperature). For larger x values, magnetizations up to 118 emu/g at 4 K are obtained.     

A thermodynamic study of the Cu-Cr-O system by the EMF method

The equilibrium oxygen pressures of the three-phase regions [Cu, Cr₂O₃, Cu₂Cr₂O₄], [Cu, Cu₂O, Cu₂O₂O₄] and [CuO, Cu₂O, Cu₂Cr₂O₄] were measured as a function of temperature by the solid oxide electrolyte electromotive force method. The measured Gibbs energy of the reaction Cu₂O+ Cr₂O₂ = Cu₂Cr₂O₄ (ΔG°) was found to be −46608 + 7.8328 T J mol⁻¹ (1075–1275 K). The evaluated Gibbs energy of formation of Cu₂Cr₂O₄ (ΔG°(inf,Cu₂Cr₂O₄)) was found to be −1332900 + 332.761 T J mol⁻¹ (900–1350 K).     

SrFe0.6Cu0.3Ti0.1O3-δ混合导体透氧材料的稳定性

利用柠檬酸络合法制备了SrFe(Cu,Ti)O_3-δ混合导体透氧材料。 采用XRD、O₂-TPD、H₂-TPR、SEM等测试技术考察了材料的稳定性。 结果表明,SrFe_0.7Cu_0.3O_3-δ在低氧压下会发生相分解,产生SrCuO₂杂相,而掺杂Ti后的SrFe_0.6Cu_0.3Ti_0.1O_3-δ在低氧压下保持单一的钙钛矿结构。 H₂-TPR和O₂-TPD的测试表明,Ti⁴⁺的掺杂提高了材料的氧脱附起始温度和其它金属离子的还原温度。 SrFe_0.6Cu_0.3Ti_0.1O_3-δ膜在透氧过程中,会有Cu²⁺和Sr²⁺从钙钛矿结构中析出,在原晶粒边界形成新的小晶粒,但这种轻微的组分偏析没有影响到材料的透氧量,此透氧膜在66 h的操作过程中显示了良好的稳定性。     

Oxygen storage capacity of delafossite-type CuLnO2 (Ln = La, Y) and their stability under oxidative/reductive atomosphere

Delafossite-type CuLnO₂ (Ln = La, Y) was synthesized and investigated their oxygen storage capacity (OSC) under oxidation/reduction cycle. CuLaO₂ was synthesized by heating at 1000 °C for 6 h in N₂ flow and CuYO₂ was synthesized by heating of Cu₂Y₂O₅ at 1190 °C for 1 h in N₂ flow. The oxygen storage capacity values of CuLaO₂ and CuYO₂ at lower temperature were larger than that of CeO₂-based materials which is used as a promoter of an automobile catalyst. The stability of delafossite-type CuLnO₂ under cyclic oxidation/reduction atomosphere was investigated using XRD analysis. During the OSC measurement up to 700 °C, CuLaO₂ decomposed to La₂CuO₄ and Cu₂O. CuYO₂ also partially decomposed to Y₂O₃, Cu₂Y₂O₅ and Cu₂O. These results suggest that oxidative decomposition of CuLnO₂ occurred at high temperature. In lower temperature range, delafossite-type CuLaO_2+x containing excess oxygen existed in both oxidative and reductive atmosphere and it partially decomposed during a hundred of oxidation/reduction cycles.     

High‐pressure synthesis of the new rare‐earth oxoborate β‐Gd2B4O9

β‐Digadolinium tetraborate (β‐Gd₂B₄O₉) was synthesized under high‐pressure/high‐temperature conditions in a Walker‐type multi‐anvil apparatus at 3 GPa and 1223 K from the pure binary oxides. Its crystal structure has been determined from single‐crystal X‐ray diffraction data collected at room temperature. The compound is isotypic with the known compound β‐Dy₂B₄O₉, which was synthesized under extreme conditions by use of a flux.     

Synthesis and ac susceptibility of YCa2Cu3O7−δ

The bulk superconducting YCa₂Cu₃O_7−δ compounds are prepared at an ordinary pressure of oxygen by conventional solid-state reaction method. The formation of sample is tested by means of XRD and is studied for their ac susceptibility below room temperature up to 77.5 K. The samples are found single-phase orthorhombic structure and found superconducting at 83.5 K. It is shown that the analysis is consistent with published data on YBa₂Cu₃O_7−δ oxide superconductor.     

Application of model of ideal solution of interaction products (ISIP) and thermodynamic modeling (TM) for description of superconducting phases in the system YBaCuO

The thermochemical properties of Cu₂O₃ were calculated. The stability of Cu₂O₃ was studied with the help of TM methods. It was shown that this oxide can exist in oxygen atmosphere (P=10⁵ Pa) at temperatures below 380 K. A variant of the ISIP model was used with TM to determine the Cu⁺, Cu²⁺ and Cu³⁺ contents and oxygen indexes in YBa₂Cu₃O_x (123-O_x), YBa₂Cu_3.5O_y (123.5-O_y), YBa₂Cu₄O_z (124-O_z), YBa₂Cu₅O_q (125-O_q) and YBa₂Cu₆O_m (126-O_m) solutions at 100–1200 K in oxygen medium (P=10⁵ Pa). Methods for determination of some thermodynamic properties and oxygen indices are suggested for a superconductor family in the system YBaCuO.     

Ternary telluride phases crystallizing in the polythermal non-quasi-binary section Cu2Cr4Te7-Te in the quasi-ternary system Cu2Te-Cr2Te3-Te

The interaction in the section Cu₂Cr₄Te₇-Te of the quasi-ternary system Cu₂Te-Cr₂Te₃-Te was studied by physicochemical analysis methods (differential thermal, X-ray powder diffraction, and microstructural analyses) and also by analyzing the temperature dependences of the specific magnetization of samples. In the section, there is a wide region of homogeneity of solid solutions based on Cu₂Cr₄Te₇, which extends at room temperature to 42 at %, and there are also regions of crystallization of two more ternary tellurides, Cu₄Cr₈Te₁₇ and CuCr₂Te₅. The characteristics of the formation and melting of the obtained phases were found. The Curie temperatures of the solid solutions based on Cu₂Cr₄Te₇ are 285–325 K, and those of Cu₄Cr₈Te₁₇ and CuCr₂Te₅ are 270 and 190 K, respectively.     

Structural study of copper-nickel aluminate (CuxNi1−xAl2O4) spinels

CuAl₂O₄, NiAl₂O₄, and three ternary spinels Cu_xNi_1?xAl₂O₃ have been prepared, in polycrystalline form, by solid-state reaction of mixtures of CuO, NiO, and Al₂O₃ at 1223 K. X-Ray powder diffractometry, coupled with adequate computational methods, allowed determination of the unit-cell length, oxygen positional parameter, and cation distribution for each compound. Interdependence of these structural parameters is closely analyzed on the ternary oxide spinels. The one-electron difference between the Cu²⁺ and Ni²⁺ ions was found to be enough to render them distinguishable by X-ray powder diffraction.     

Synthesis and Structural Determination of the Disordered Bixbyite Cu3‐xSb1+xO5.5+3x/2 with Spin‐Glass Behaviour

The ternary copper antimony oxide Cu_3‐xSb_1+xO_5.5+3x/2 (x=0.23) has been synthesized under 0.8–1.3 MPa pO₂ at 1022–1082 °C. Rietveld refinements of X‐ray and neutron powder diffraction patterns concluded that the oxide adopts a bixbyite type structure, crystallising in the cubic space group Ia‐3 with the unit cell parameter a=9.61164(4) Å at room temperature from powder neutron diffraction data. The cationic 8b and 24d sites were found to be occupationally disordered where both Cu and Sb could be found on both sites. This is supported by X‐ray absorption spectroscopy experiments showing more than one possible Cu environment. There was a significant net deficiency of oxygen in the compound which was first inferred from observations of a thermochromic‐like phenomena and also seen from in situ high temperature neutron diffraction experiments. Magnetic susceptibility and magnetization measurements show paramagnetic behaviour with spin‐glass like transition below 6 K.     

Thermogravimetric study of the nonstoichiometric regions in the Y-Ba-Cu-O system

The paper presents the results of studies on thermal reduction and oxidation of the nonstoichiometric phases from the Y-Ba-Cu-O in air.The thermogravimetric (TG, DTA) experiments were performed in air in order to establish the ranges of stoichiometry and temperature of oxidation and reduction of YBa₂Cu₃O_x, YBa₄Cu₃O_x, YBa₅Cu₂O_x and Y₃Ba₈CusO_x.It has been found, that at 950°C in air there are four oxygen deficient ternary cuprates: YBa₂Cu₃O_6.02, YBa₄Cu₃O_8.01, YBa₅Cu₂O_8.35, Y₃Ba₈Cu₅O_16.45 and stoichiometric Y₂BaCuO₅. When these nonstoichiometric cuprates are cooled slowly to room temperature in air they oxidize to the following compositions: YBa₂Cu₃O_6.98, YBa₄Cu₃O_8.97, Y₃Ba₈Cu₅O₁₈ and YBa₅Cu₂O_8.97.This work has been supported by the CPBR 6.6.64 research programme.     

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.     

Synthesis and crystal structure of a 1D chain polyoxometalate-based complex {[CuI(en)2(H2O)]2{GeW12O40[CuII(en)2]} · 2.5H2O} n

A 1-D infinite chain organic–inorganic hybrid compound, [Cu^I(en)₂(H₂O)]₂{GeW₁₂O₄₀[Cu^II(en)₂]}·2.5H₂O, was synthesized hydrothermally and characterized by IR, UV spectroscopy, TG analyses, and single-crystal X-ray diffraction. Structural analysis indicates that neighboring [GeW₁₂O₄₀]^4? polyanions are interconnected by [Cu(3)(en)₂]²⁺ subunits via W–O_t–Cu(3) bridges, generating a 1D infinite chain structure. Furthermore, the compound shows photoluminescence in the solid state at room temperature.     

Sol-Gel Synthesis Route for the Preparation of Y(Ba1−x Sr x )2Cu4O8 Superconducting Oxides

Superconducting oxide ceramics of composition Y(Ba_1–x Sr _x )₂Cu₄O₈ (x = 0.00, 0.10, and 0.20) have been prepared by a simple sol-gel method based on the complexation of metal ions in aqueous medium, by chelating acetate and tartarate ligands. Homogeneous sols were obtained by complexing copper ions with tartaric acid, which prevented the flocculation of copper acetate during the gelation process. Single-phase bulk samples were obtained after firing the mixed-metal polymeric acetate-tartarate precursor to 835°C for 70 h in flowing oxygen atmosphere. Thermal decomposition of the gels was studied by thermogravimetry. Effect of strontium substitution on the properties of the compounds was studied by X-ray powder diffraction, electron microscopy, X-ray photoemission spectroscopy and resistivity measurements. These data indicate that nearly monophasic Y(Ba_1–x Sr _x )₂Cu₄O₈ superconducting samples were obtained for x < 0.30. The Sr-doping in the YBa₂Cu₄O₈ (Y-124) phase shows a pronounced effect on the superconducting properties enhancing the critical temperature from 78 K (for the non-substituted sample) to 88 K (for Y(Ba_1–x Sr _x )₂Cu₄O₈).     

A Novel Family of Cage-like (CuLi,CuNa, CuK)-phenylsilsesquioxane Complexes with 8-Hydroxyquinoline Ligands: Synthesis,Structure, and Catalytic Activity

The first examples of metallasilsesquioxane complexes, including ligands of the 8-hydroxyquinoline family 1–9, were synthesized, and their structures were established by single crystal X-ray diffraction using synchrotron radiation. Compounds 1–9 tend to form a type of sandwich-like cage of Cu₄M₂ nuclearity (M = Li, Na, K). Each complex includes two cisoid pentameric silsesquioxane ligands and two 8-hydroxyquinoline ligands. The latter coordinates the copper ions and corresponding alkaline metal ions (via the deprotonated oxygen site). A characteristic (size) of the alkaline metal ion and a variation of characteristics of nitrogen ligands (8-hydroxyquinoline vs. 5-chloro-8-hydroxyquinoline vs. 5,7-dibromo-8-hydroxyquinoline vs. 5,7-diiodo-8-hydroxyquinoline) are highly influential for the formation of the supramolecular structure of the complexes 3a, 5, and 7–9. The Cu₆Na₂-based compound 2 exhibits high catalytic activity towards the oxidation of (i) hydrocarbons by H₂O₂ activated with HNO₃, and (ii) alcohols by tert-butyl hydroperoxide. Studies of kinetics and their selectivity has led us to conclude that it is the hydroxyl radicals that play a crucial role in this process.     

Oxygen Plasma Effects on Zero Resistance Behavior of Yb,Er‐doped YBCO (123) Based Superconductors

Rare‐earth doped YBa₂Cu₃O_7–δ samples were synthesized starting from the corresponding oxides Y₂O₃, Yb₂O₃, Er₂O₃, CuO as well as Ba(OH)₂ by heating to 950 °C under air. The doping concentrations were adjusted to 15 % Yb, 7 % Er and 20 % Yb, 15 % Er, respectively, with respect to the yttrium content. The orthogonal phased (123) YBCO ceramics were exposed to an oxygen plasma for 140 and 380 min. Zero resistance temperature (T_c,0) was determined by measuring the resistivity‐temperature dependence using a classical four point measurement approach. Under optimal conditions with respect to the material composition and the oxygen treatment an unusual high zero resistance temperature of 97.5 K (T_c,onset ≈ 101 K) was achieved. This represents an increase of T_c,0 by 7.5 K. The oxygen treatment could not be monitored by IR spectroscopy, X‐ray fluorescence spectroscopy, and X‐ray powder diffraction. The results showed good reproducibility.     

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.     

Synthesis, structural and electrical characterizations of DySr5Ni2.4Cu0.6O12−δ

A new compound DySr₅Ni_2.4Cu_0.6O_12−δ has been prepared by sol gel method and annealed at 1473 K in 1 atm of Ar gas flow. The X-ray diffraction (XRD) is used for phase identification. The sample shows to adopt the K₂NiF₄-type structure based on tolerance factor calculation. XRD analysis using the Rietveld method was carried out and it was found that DySr₅Ni_2.4Cu_0.6O_12−δ (Dy_0.33Sr_1.67Ni_0.8Cu_0.2O_4−δ′) compound crystallizes in tetragonal symmetry with space group I4/mmm (Z=2). The lattice parameters are found to be at room temperature a=3.7696(5) Å and c=12.3747(2) Å. The final reliability indices were: R_B=5.219% and χ²=3.47. Four probe electrical resistivity measurements were performed versus temperature in the range 294–579 K. A semiconducting behaviour over the whole range of temperature, with a conductivity maximum of 0.4 S cm⁻¹ is observed at 510 K.