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.     

Existence of the homologous series of Y n Ba m Cu m + n O y (m = 2, 3, 5; n = 1, 2) oxides with the tetragonal and orthorhombic structures of YBa2Cu3O6 + δ

The phase composition of Y _x Ba_1?x CuO _y (x = 0.29?0.40) samples annealed in air (at 930?C990°C) and in an oxygen atmosphere (450?C800°C, P(O₂) = 101 kPa) was studied by X-ray powder diffraction, chemical analysis, electron diffraction, and elemental analysis in a transmission electron microscope. A considerable cation nonstoichiometry was discovered in particles having the tetragonal and orthorhombic structures of YBa₂Cu₃O_{6 + ??}. The variation range of particle compositions comprises matrix oxides of the Ba _m Cu _{m + n} O _y series with (Ba: Cu) 3: 5, 5: 8, 2: 3, and 5: 7, which in the presence of yttrium form the Y _n Ba _m Cu _{m + n} O _y series. Tetragonal oxides Y₂Ba₃Cu₅O _y (235), Y₃Ba₅Cu₈O _y (358), YBa₂Cu₃O _y (123), and Y₂Ba₅Cu₇O _y (257) are formed at the primary synthesis step in air and are preserved in an orthorhombic structure during short-term (1 h) oxygen annealing. Most particles of the 3: 5 and 5: 8 oxides are undersaturated with yttrium relative to the stoichiometry of the Y _n Ba _m Cu _{m + n} O _y series, those of the 2: 3 oxide correspond to this stoichiometry, and those of the 5: 7 oxide are supersaturated with yttrium over the stoichiometry. A trend is observed for the fractions of these oxides to change during long-term (5?C51 h) annealing in an oxygen atmosphere at 450°C and to the alternation of the dominant role of one of the four phases with the superconducting transition temperature T _c = 82, 85, 86, and 91 K. Each orthorhombic oxide undergoes structural transformations during oxygen annealing with a change in T _c. The coexistence of these oxides in the form of nanometer-sized domains does not allow their individual superstructures to be recognized.     

Über Oxocuprate. XI. Zur Kenntnis von Ba3Cu2O4Cl2

On Osocuprates. XI. Ba₃Cu₂O₄Cl₂ A new oxohalogenocuprat, Ba₃Cu₂O₄Cl₂ mas prepared and investigated by X-ray single crystal methods. The hitherto unknown compound has orthorhombic symmetry (Space group: D_2h⁵—Pmma; a = 6.653, b = 6.000, c = 10.563 Å). It shows angled chains of O^2?-squares around Cu²⁺. One of the Cu²⁺ positions is completed by Cl^minus; to a tetragonal pyramid. The coordination polyhedrals of Ba_I–III and the connection with the Cu/O-chains are described and discussed.     

Phases in the System Ba2M2-xCuxO4+δ, M = In,Sc: Structure and Oxygen Stoichiometry

Members of the series Ba₂M_2-x,Cu_x O_4+δ, M = In, Sc (0 ≤ x ≤ 1), have been synthesised by solid-state reaction methods and products characterized by powder X-ray diffraction (PXD). Selected compounds have been annealed under oxygen at 1 atm and oxygen stoichiometries for unannealed and oxygen annealed samples have been calculated following thermogravimetric analysis (TGA). Structures for M = In, x = 0, 0.5, 1 and M = Sc, x = 1 were determined by Rietveld analysis of PXD data. Ba₂In₂O₅ has been shown to crystallize in the orthorhombic space group Ibm2 (Brownmillerite structure) with a = 6.0956(1) Å, b = 16.7112(3) Å c = 5.9601(1) Å. The copper-containing phases adopt a tetragonal "doubled perovskite" structure built up of copper-substituted BaInO_2.5 cubes. The copper coordination and oxidation state can be controlled by varying the oxygen level of the structure.     

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).     

Spectrophotometric determination of oxygen content in calcium substituted RBCO (R=Eu,Gd, Er) superconductors

The oxygen stoichiometry in R_1−x Ca _x Ba₂Cu₃O _y (R=Eu, Er, Gd; x=0, 0.2, 0.25, 0.3) superconducting bulk samples was determined spectrophotometrically. The dependence of the critical temperature on the y-oxygen coefficient and the x-coefficient of the included calcium was studied.     

Phase formation and microstructure in Re1-x CaxBa2Cu3Oz (Re=Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics

We have investigated the influence of Ca-substitution and different rare earths on the microstructure of RE_1-x Ca_xBa₂Cu₃O_7-δ (RE= Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics. Scanning electron microscopy, X-ray microanalysis and energy dispersive spectroscopy have been used to study the microstructure and the chemical composition of the samples. A correlation was established between the polycrystalline microstructure and phase formation depending on the additive content. We observed that calcium is distributed uniformly in the crystals. The formation of minor impurity phases improved the sintering conditions.     

Ein alternativer Weg zur Darstellung von Bi2Sr2CaCu2Ox,YBa2Cu3O7−δ, und YBa2Cu3−xMxO7−δ (M  Ni,Ag und x ≤ 33 Mol%)

An Alternative Method for Preparation of Bi₂Sr₂CaCu₃O_x, YBa₂Cu₃O_7?δ, and YBa₂Cu_3?xM_xO_7?δ (M ? Ni, Ag and x ≤ 33 Mol%) Oxidation of quenched melts of metals in a well defined argon/oxygen atmosphere has been found as an alternative method to prepare hight purity samples of Bi₂Sr₂CaCu₂O_x without Pb-stabilization. A special equipment for the oxidation of powder samples will be described. By our new method it is also possible to prepare YBa₂Cu₃O_7?δ and derivatives of this compound, where Cu is substituted by high amounts of Ni or Ag.     

Property characterization and formation mechanism of anticorrosion film coated on AZ31B Mg alloy by SNAP technology

Despite tremendous efforts in research and development after the discovery of high-temperature perovskite-type layered superconductors, and high expectations expressed in market projection potential electrical commercial applications of these materials, the popularity of these superconductors is taking off very slowly. One of the biggest hurdles facing the widespread application of the (RE)Ba₂Cu₃O₇ is developing a manufacturing process of flexible multifilamentary coated conductors, comprised of a buffered metallic substrate and a superconducting layer (Glowacki, in Frontiers in Superconducting Materials. Springer, New York, 2005), that will produce it in long lengths and at prices competitive with copper for applications such as motors, generators, transmission cables, and other power systems (Lectures on Superconductivity, University of Cambridge, Cambridge, 2008). The low-cost powder-in-tube or screen-printing processes, that are successful in the manufacturing of medium temperature superconductor MgB₂ and high-temperature Bi-family superconductors cannot be used for (RE)Ba₂Cu₃O₇ conductors due to their granularity and ceramic-like mechanical bulk properties. Deposition of a (RE)Ba₂Cu₃O₇ coating using physical deposition techniques is too expensive to provide low-cost highly textured coated conductor for AC applications (Lectures on Superconductivity, University of Cambridge, Cambridge, 2008). Therefore, the obvious choice is the chemical route and the sol gel deposited using ink-jet printing (Glowacki, in Frontiers in Superconducting Materials. Springer, New York, 2005; Lectures on Superconductivity, University of Cambridge, Cambridge, 2008) is currently recognised as potentially the best way to manufacture 3D multifilamentary high temperature superconductor (Glowacki, in Frontiers in Superconducting Materials. Springer, New York, 2005). In this paper the perspective of deposition of buffer layer and multifilamentary (RE)Ba₂Cu₃O₇ superconducting layer by sol gel ink-jet printing is discussed with respect to best conductor AC performance, and also addresses the future research that is required.     

Ba2Ca2Cu3Ox Precursor Effects on Synthesis of (Hg,Pb)Ba2Ca2Cu3O8+δ Superconductor

The influence of Ba₂Ca₂Cu₃O_x precursor on the synthesis and properties of (Hg,Pb)Ba₂Ca₂Cu₃O_8+δ has been examined. Fine homogeneous Hg-free precursor powder of Ba₂Ca₂Cu₃O_x of desirable phase composition was prepared by sol-gel method using EDTA acid as a complexing agent. A reproducible superconducting sample of Hg_0.8Pb_0.2Ba₂Ca₂Cu₃O_8+δ with fine-grained, dense microstructure, composed predominantly of (Hg,Pb)-1223 phase and with advantageous magnetic properties, was synthesized by high pressure crystallization in mercury environment of well-calcined Ba₂Ca₂Cu₃O_x precursor. This revised version was published online in July 2006 with corrections to the Cover Date.     

Les oxydes A2BaCuO5 (A = Y,Sm, Eu,Gd, Dy,Ho, Er,Yb)

A series of new phases, A₂BaCuO₅ (A = Y, Sm, Eu, Gd, Dy, Ho, Er, Yb), has been isolated. These compounds are orthorhombic, with $\text{a ? 7.1, b ? 12.2}$, and $\text{c ? 5.6}$Å. The probable space groups deduced from the electron diffraction patterns are Pbnm and Pbn2₁. The structure has been resolved from X-ray powder patterns. The framework can be considered as built up from distorted monocapped trigonal prisms AO₇ which share one triangular face forming A₂O₁₁ blocks. The edge-sharing A₂O₁₁ blocks form a three-dimensional network which delimits cavities where Ba²⁺ and Cu²⁺ are located. Barium is coordinated to 11 oxygen atoms, while the coordination polyhedron of copper is a distorted tetragonal pyramid CuO₅.     

Thermodynamic properties and oxygen stoichiometry of Ba2Cu3O5 + δ

The thermodynamic properties and oxygen stoichiometry of Ba₂Cu₃O_{5 + δ} are studied by means of the electromotive force (EMF) with a fluoride electrolyte, dissolution calorimetry, and thermogravimetry. It is shown that the temperature dependence of the Gibbs energy of the formation of barium cuprate from simple oxides and oxygen in the temperature range of 860–1120 K can be described by the polynomial Δ_{f, ox} G ^°(Ba₂Cu₃O_{5 + δ}) ± 0.1 (kJ/mol) = ?291.78 + 1.127T ? 0.13207 TlnT (kJ/mol).     

Das Kupfer(II)-oxidphosphat Cu4O(PO4)2 in einer neuen,orthorhombischen Modifikation durch Oxidation einer Tl/Cu/P-Legierung

The Copper(II) Oxide Phosphate Cu₄O(PO₄)₂ in a New, Orthorhombic Modification by Oxidation of a Tl/Cu/P Alloy Single crystals of Cu₄O(PO₄)₂ in a new, orthorhombic modification were prepared by reaction of a Tl/Cu/P alloy with oxygen. The compound crystallizes in the space group Pnma with Z = 4 and lattice constants a = 808.8(5) pm, b = 627.0(7) pm, c = 1338.3(1) pm. It is isotypic with the orthorhombic form of Cu₄O(AsO₄)₂. The copper atoms are five-coordinated by oxygen. The distorted square-pyramidal and trigonal-bipyramidal polyhedra are connected by edges and vertices to form [Cu₈O₁₈] ribbons running along [010] and forming slabs perpendicular to the c-axis interconnected by phosphate groups.     

Ruthenium(V) Oxides from Low‐Temperature Hydrothermal Synthesis

Low‐temperature (200 °C) hydrothermal synthesis of the ruthenium oxides Ca_1.5Ru₂O₇, SrRu₂O₆, and Ba₂Ru₃O₉(OH) is reported. Ca_1.5Ru₂O₇ is a defective pyrochlore containing Ru^V/VI; SrRu₂O₆ is a layered Ru^V oxide with a PbSb₂O₆ structure, whilst Ba₂Ru₃O₉(OH) has a previously unreported structure type with orthorhombic symmetry solved from synchrotron X‐ray and neutron powder diffraction. SrRu₂O₆ exhibits unusually high‐temperature magnetic order, with antiferromagnetism persisting to at least 500 K, and refinement using room temperature neutron powder diffraction data provides the magnetic structure. All three ruthenates are metastable and readily collapse to mixtures of other oxides upon heating in air at temperatures around 300–500 °C, suggesting they would be difficult, if not impossible, to isolate under conventional high‐temperature solid‐state synthesis conditions.     

Estimation of melting (decomposition) heat of some compounds in the Y−Ba−Cu−O system

A thermodynamical method for the estimation of decomposition heat in a crystal state, incongrous and congruous melting of compounds with the use of temperature dependencies of total entropies of compounds was suggested. Entropies and heats of phase transformation of YBa₂Cu₃O₆, YBa₂Cu₃O₇, YBa₂Cu_3.5O_7.5, YBa₂Cu₄O₈, YBa₂Cu₅O₉, YBa₄Cu₃O_8.5, Y₂BaO₄, Y₂Ba₂O₅, Y₂Ba₄O₇, Y₄Ba₃O₉, YCuO₂, Y₂Cu₂O₅, Y₂BaCu₂O₅, Ba₂CuO₃, BaCuO₂, BaCu₂O₂, Ba₃Cu₅O₈ were calculated. Data, obtained by the authors earlier, are discussed.     

Preparation of YBa2Cu3O y crystals by electrolysis of YO1.5-BaO-CuO x melts

Mass transfer during the electrolysis of melts of Y_0.02Ba_0.30Cu_0.70O _y and Y_0.02Ba_0.25Cu_0.75O _y samples was studied at 950°C (for 0.5 h) and currents of 5–1050 mA. YBa₂Cu₃O_{6 + δ} (123) tetragonal oxide crystal boules were grown, and their cationic composition and structure were studied by X-ray powder diffraction and by electron diffraction and elemental analysis in a transmission electron microscope (ED/TEM and EA/TEM). The 123 oxide was found to have cationic off-stoichiometry and to have a domain structure with domain sizes of 20–50 Å. Magnetic susceptibility versus temperature curves measured in the crystals after oxygen annealing (450°C, 1 h) feature four kinks, which indicate the occurrence of four superconducting phases with T _c = 45, 52, 75, and 86 K. Electrolysis byproducts are platinum-containing oxides Ba₉Pt₄Cu₃O _y and Ba₅₀Pt₁₅Y₁₆Al₁₃Cu₇O _y unknown hitherto; we report structure data for them.     

Electronic structure and properties of isolectronically substituted compounds Y1Ba2−m M m Cu3O7 and Y1Ba2−m M m Cu4O8 (M=Be,Mg, Ca,Sr, Ba,Ra)

According to cluster calculations, the electronic structures of compounds based on Y₁Ba₂Cu₃O₇ and Y₁Ba₂Cu₄O₈ with isoelectronically substituted barium have some qualitative distinctions. These compounds behave differently upon barium substitution by other elements due to differences in the character of their highest occupied and lowest unoccupied molecular orbitals. Substitution of barium by radium is expected to lead to an increase in oxygen stability without a significant decrease in the critical temperature of superconduction transition T_s. In order to raise T_s, it is of interest to study the systems YBa_2−m(Be or Mg)_mCu₃O_x and YBa_2−m(Ca, Sr)_mCu₃O_x. On partial substitution of barium by calcium in YBa₂Cu₄O₈, the mechanism of T_s elevation may involve contraction of the forbidden band due to oxygen sublattice distortions in the vicinity of Ba centers. D. I. Mendeleev Russian Chemical Engineering University, Novomoskovsk Branch. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 2, pp. 24–31, March–April, 1994. Translated by O. Kharlamova     

Oxygen non-stoichiometry and diffusion in RBA2CU3O6+x (R=Y, Gd, Ho) investigated by TG method

By means of thermogravimetry (TG) and chemical analysis equilibrium dependencies of oxygen content in GdBa₂Cu₃O_6+x and HoBa₂Cu₃O_6+x on temperature and were studied. It is found that at equal temperature and the oxygen content in RBa₂Cu₃O_6+x increased in order Ho-Y-Gd.On the basis of Fick 2nd law mathematical procedures to determine diffusion coefficients of oxygen from TG data were developed. The oxygen diffusion coefficients in RBa₂Cu₃O_6+x (R=Y, Gd, Ho) were evaluated in a wide temperature (300–900°C) range (at =0.21 bar). The developed model rather satisfactory decribes oxygen diffusion processes in phases under investigation. It is found that for all studied compounds oxygen diffusion in orthorhombic phase happened faster than in tetragonal one. The values of diffusion coefficients increase in order Ho-Y-Gd with increasing of ionic radius of the rare earth element.     

Das erste Alkali-Erdalkali-Oxocuprat(II,III): NaBa2Cu22+Cu3+O6

The first Alkaline Alkaline-Earth Oxocuprate (II, III): NaBa₂Cu₂²⁺Cu³⁺O₆ The compound NaBa₂Cu₃O₆ was prepared by heating of Na₂O₂, BaO₂, Cu₂O in closed Ag-tubes. X-ray single crystal investigations led to orthorhombic symmetry, space group D-Fmmm; a = 8.4229; b = 11.4418; c = 14.4063 Å; Z = 8. Cu²⁺ and Cu³⁺ show square planar polygones of four and Na⁺ trigonal prisms of six O^2?. The two barium point positions show coordination numbers C.N. = 8 and 6 + 4. The crystal structure is discussed.     

High Pressure Synthesis and Characterization of New Members of the RuSr2(RE,Ce)2Cu2O10 Family (RE = Y,Dy)

New members of the RuSr₂(RE_2?x, Ce_x)Cu₂O₁₀ family of magnetically ordered phases have been synthesized under high pressure / high temperature conditions for RE = Y (x = 0.5, 0.7) and Dy (x = 0.5). All compounds show tetragonal symmetry with cell parameters a ≈ 3.82 Å and c ≈ 28.4 Å. Magnetic susceptibility vs temperature measurements show ferromagnetic behaviour of these compounds with T_M = 120–140 K, depending on Ce content. These compounds are semiconducting and tend to transform into insulator, by increasing Ce content, as observed by the temperature dependence of the resistance.