Über die Polymorphie der Perowskite Ba2SE0,67WVIO6. II. Die Systeme Ba2Nd0,67(1−x) Y0,67xWO6 und Ba2Nd0,67W1−xUxO6

Polymorphism of Perovskite Compounds Ba₂SE_0.67W^VIO₆. II. The Systems Ba₂Nd_0.67(1?x)Y_0.67xWO₆ and Ba₂Nd_0.67W_1?xU_xO₆ In the system Ba₂Nd_0.67(1?x)Y_0.67xWO₆ the formation of a continuous series of mixed crystals with cubic 1:1 ordered perovskite structure is observed. The existence of a hexagonal modification is confined to the Y-rich side (x ≥ 0,9). In the Ba₂Nd_0.67W_1?xU_xO₆ series only for x ? 0,25 homogeneous cubic perovskites are obtained. In contrast to systems with other rare earths the Nd series show uncommon optical properties.     

Über Das System Ba2Gd2/3□1/3U1−xWxO6 sowie hexagonale Perowskite vom 18-

On the System Ba₂Gd_2/3□_1/3U_1?xW_xO₆ and Hexagonal Perovskites of an 18-Layer Type In the system Ba₂Gd_2/3□_1/3U_1?xW_xO₆ the formation of a continuous solid solution series is observed. With x ? 0.9 the mixed crystals have a cubic 1:1 ordered perovskite structure. With x ≥ 0.95 the compounds are polymorphic: besides an cubic 1:1 ordered perovskite type for x = 0.95; 0.99 and 1.00 one hexagonal layer structure exists. This lattice is in all cases rhombohedral (space group R3 m) and represents an 18 L-type. Likewise the compounds Ba₂B□_1/3W^VIO₆ with B^III = Tb-Lu and Y belong to the 18 L-type.     

Thermal analysis of Y1−xCaxBa2Cu3O7−y

TG and DTA analysis of Y_1?xCa_xBa₂Cu₃O_7?y suggests that the stability of the 123 phase increases with increasing Ca contents. The O(1) in the Cu(1)-O chain is unstable but O(2) and O(3) in Cu(2)-O planes are very stable. There are hardly any oxygen vacancies in the Cu(2)-O plane. The replacement of Y by Ca does not make oxygen vacancies in Cu(2)-O planes but leads to an increase in the oxidation number of copper in Cu(2)-O planes.     

Über Perowskitphasen des Systems Ba2Y0,67U1−xWxO6

On Perovskite Phases of the System Ba₂Y_0,67U_1?xW_xO₆ A solid solution series is formed between the polymorphic perovskites Ba₂Y_0.67UO₆ and Ba₂Y_0.67WO₆ (cubic: a = 8.37₂ Å; hexagonal: a = 4× 5.88₁ Å and c = 4× 7.77₈ Å). The structure is cubic between x = 0.1 and 0.99 and for x > 0.95 hexagonal as well. Strong deviations from the ideal behaviour are detectabel with spectroscopic methods. The shape of the UO₆ and WO₆ octahedrons experiences only minor changes within the series.     

Ceramic electrolytes based on (Ba1 − x Ca x )(Zr0.9Y0.1)O3 solid solution

The aim of this work was to study the electrical and electrochemical properties of the (Ba_1???x Ca _x )(Zr_0.9Y_0.1)O₃ solid solutions. The powders of different calcium content (x?=?0, 0.05, 0.1, and 1) were prepared by a thermal decomposition of organo-metallic precursors containing ethylenediaminetetraacetate acid. X-ray diffraction analysis showed that a small substitution of calcium for barium caused formation of cubic solid solutions with the decreasing cell parameters. Electrical conductivity measurements were performed by the d.c. four-probe method in controlled gas atmospheres containing Ar, air, H₂, and/or H₂O at temperature from 300 to 800 °C. It was found that the conductivity depended on a chemical composition of the samples and the atmosphere. Overall, the electrical conductivity was higher in wet atmospheres that contained oxygen that was in accordance with the model of a proton transport in perovskite structure which assumed the presence of the oxygen vacancies. The solid solution containing 5 mol% of calcium showed the highest conductivity and the lowest activation energy of conductivity regardless of the atmospheres; this can be attributed to the local changes in the cubic perovskite structure. Test results for CaZr_0.9Y_0.1O₃ used as an electrolyte in solid oxide galvanic cells involving CaCr₂O₄ as a reference electrode are also reported.     

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.     

Ba2Cu3O5+δ as an intermediate phase during the synthesis of YBa2Cu4O8

We propose a reaction model for the synthesis of YBa₂Cu₄O₈ under normal pressure conditions, which contains 4 partial reaction steps. In a first step bariumnitrate and copperoxide react to Ba₂Cu₃O_5+δ. This substance will be formed for each mixtures Ba:Cu=2∶3...3∶2. The following two partial reaction steps are connected to Ba₂Cu₃O_5+δ, which reacts with Y₂O₃ and CuO to YBa₂Cu₄O₈ or decomposes to BaCuO₂ and CuO. In a last step parts of BaCuO₂ reacts with Y₂O₃ and CuO to YBa₂Cu₄O₈.     

Magnetic studies on (U,La)O2+x solid solutions

Magnetic susceptibilities of La_yU_1−yO_2+x solid solutions with fluorite structure were measured from 4.2 K to room temperature. An antiferromagnetic transition was observed for the solid solutions with lanthanum concentration0 ≤ y ≤ 0.3 in both stoichiometric (x = 0) and hypostoichiometric oxygen range (x < 0). From comparison of the magnetic properties of solid solutions with different oxygen amounts (x < 0, x = 0, x > 0), both oxygen vacancies and interstitial oxygens were found to weaken the magnetic exchange interactions between uranium ions. The Ne´el temperature decreased with decreasing uranium concentration. The variation of the Ne´el temperature of (U, La)O₂ solid solutions with uranium concentration was different from that of (U, Th)O₂ solid solutions. The magnetic moment decreased with decreasing uranium concentration. Its rate was larger than that of (U, Th)O₂ solid solutions and was comparable with that of (U, Y)O₂ solid solutions. The oxidation state of uranium in the solid solutions was examined from the magnetic susceptibility data. The uranium ions were found to be in either the tetravalent or the pentavalent state. The effect of magnetic dilution was larger with La₂O₃ than with Y₂O₃ and/or Sc₂O₃.     

Complex copper(II) fluorides. XV. The Ternary System BaF2?CuF2?ScF3

The liquid-solid phase diagram of the binary system BaF₂? ScF₃ is established by D.T.A. and radiocrystallography. Three fluorides are disclosed: Ba₃Sc₂F₁₂, Ba₅Sc₃F₁₉ and a cubic high temperature phase Ba_1?xSc_xF_2+x (x = 0.17), the structure of which derives from that of BaF₂. A solid solution between BaF₂ and ScF₃ is also evidenced at high temperature. The ternary system BaF₂? CuF₂? ScF₃ is investigated by radiocrystallography and an isothermal section at 670°C is given. It shows the existence of four phases: a complex quaternary fluoride Ba₁₀Cu₁₂ScF₄₇, two “polytypic” phases the structure of which derives from that of BaCuF₄ and a tetragonal solid solution Ba₅Sc_3?xCu_xF_19?x with 0 ≤ x ≤ 1.     

Mechanochemical synthesis and thermal stability of phases in the Y2O3–Yb2O3 system

Substitutional, continuous solid solution of the general formula Y_2–xYb_xO₃ was obtained from the mixture of Y₂O₃ and Yb₂O₃ oxides, for the first time by the mechanochemical method in a high-energy ball milling. The monophasic samples of nanocrystalline solid solution for x?>?0.00 and x?<?2.00 were examined by the methods: XRD, DTA, SEM, IR and UV–Vis–DR. As follows from the results, the solid solution crystallizes in cubic system and is isostructural with Y₂O₃ and Yb₂O₃. The solution is stable in the air atmosphere up to at least 900°C, and its decomposition temperature decreases with the increase in x, that is, with decreasing number of Yb³⁺ ions replacing Y³⁺ ions in the crystal lattice of Y₂O₃. The energy band gap estimated for the solid solution varies from?~?5.30 eV for x?=?0.50 to?~?4.90 eV for x?=?1.50, which means that it is an insulator.

     

Über das System Ba2Zn1−xCuxUO6 — ein schwingungsspektroskopischer Nachweis des Jahn-Teller-Effekts

On the System Ba₂Zn_1?xCu_xUO₆. A Vibrational Spectroscopic Proof of the Jahn Teller Effect The ordered perovskites Ba₂ZnUO₆ (cubic, space group Fm3m) and Ba₂CuUO₆ (tetragonal, space group I₄/mmm) form solid solutions. For small Cu content the lattice symmetry is cubic, with x ≥ 0.25 an increasing tetragonal distortion (c/a √2 > 1) is observed. From the vibrational spectra and in accordance with the factor group analysis the symmetry of the UO₆ octahedra is for small Cu content O_h and on the Cu-rich side D_4h. In the region of the lattice vibrations (T₂ field) the lifting of the degeneracy — due to the Jahn Teller effect of Cu²⁺ — leads to a band separation, which decreases with sinking copper content. Therefore the Jahn Teller effect is easily noticeable with vibrational spectroscopic methods. In the corresponding series with W^VI the vibrational spectroscopic investigations lead qualitatively to the same results as in the U^VI system. As further examples the stacking polytypes Ba₂ZnTeO₆ and Ba₂CuTeO₆ are considered. The vibrational spectra show, that the Jahn Teller effect in this lattice, which is strengthened by partial face-sharing of octahedra, is less pronounced than in the perovskites in which only corner-sharing is present.     

Gibt es „Wolframylgruppierungen”︁? Über Perowskitphasen im System Ba2Y0,67UO6?Ba2CaWO6

Do ? Wolframyl Groups ”? Exist? On Perovskite Phases in the System Ba₂Y_0,67UO₆ ? Ba₂CaWO₆ In the system Ba₂Y_{0.67(1? x)}Ca_xU_{1? x}W_xO₆ a solid solution series is formed up to x ? 0.85. The properties are studied by x-ray and spectroscopic methods.     

Preparation of Y2Ba4Cu7O15-δ Superconductor without High Oxygen Pressure

The synthesis of bulk Y₂Ba₄Cu₇O_15-δ superconductor at atmospheric oxygen pressure via solid state sintering is reported. Temperature ranging from 860 to 890 °C as well as time interval over 2 to 15 days were used to investigate the formation of the Y₂Ba₄Cu₇O_15-δ phase. A time-temperature profile characterizing the conditions for the preparation of Y₂Ba₄Cu₇O_15-δ phase suggests the optimal condition to be sintering at 890 °C for over 10 days. Detailed results of X-ray diffraction, electrical resistivity, iodometric titration and magnetization measurements are described.     

Characterization of phase transition of Ba2-xSrxIn2O5 by thermal analysis and high temperature X-ray diffraction

The phase transitions of Ba_2-xSr_xIn₂O₅ were investigated with various thermal analyses and high-temperature X-ray diffraction. It was clarified that crystal structure of Ba_2-xSr_xIn₂O₅ with x=0.0~0.4 varies from brownmillerite through distorted perovskite to another distorted perovskite with increase of temperature. The phase transition from brownmillerite to distorted perovskite was revealed to be first order, whereas transition from distorted perovskite to another one was second order. The specimen with x≥0.5 showed only one first order phase transition from brownmillerite to distorted perovskite. The phase diagram of Ba_2-xSr_xIn₂O₅ was established and existence of tricritical point at ~1100°C with x=0.4~0.5 was suggested. This revised version was published online in August 2006 with corrections to the Cover Date.     

The synthesis and properties of solid solutions based on Ba<Subscript>4</Subscript>Ca<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>11</Subscript>

(Ba_{1 ? x} Ca _x )₆Nb₂O₁₁ solid solutions were synthesized. The compositions were shown to be single-phase at 0.23 ≤ x ≤ 0.47 and have a double perovskite cubic structure with an incomplete oxygen sublattice. The interaction of solid solutions with water vapor and their electrical properties were studied. In dry atmosphere, these complex oxides were mixed oxygen-hole conductors. In humid atmosphere, they intercalated water and exhibited protonic conductivity. The influence of Ba/Ca isovalent substitution, the dynamics of the oxygen sublattice, and the concentration of intercalated water on the value and contribution of protonic and hole conductivity was analyzed.     

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).     

Phase equilibria of the Ba-Sm-Y-Cu-O system for coated conductor applications

The complex phase relationships near the BaO-poor region of the quaternary Ba-Sm-Y-Cu-O oxide system prepared in pure air (O₂p=22 kPa, 950 °C) and in 0.1% O₂ (O₂p=100 Pa, 810 °C) have been determined. This investigation also included the subsolidus compatibilities in ten subsystems (Ba-Sm-Y-O, Ba-Sm-Cu-O, Ba-Y-Cu-O, Sm-Y-Cu-O, Ba-Sm-O, Ba-Y-O, Ba-Cu-O, Sm-Y-O, Sm-Cu-O, and Y-Cu-O), and the homogeneity range of five solid solutions (Ba(Sm_xY_2−x)CuO₅, (Sm,Y)₂O₃, (Sm,Y)₂CuO₄, (Y,Sm)₂Cu₂O₅, and Ba(Sm,Y)₂O₄). The single phase range of the superconductor solid solution, (Ba_2−xSm_x)(Sm_1−yY_y)Cu₃O_6+z, and the phase compatibilities in its vicinity, which are particularly important for processing, are described in detail. The phase equilibrium data of the Ba-Sm-Y-Cu-O system will enable the improvement of the intrinsic superconducting properties of second-generation wires, and facilitate the flux-pinning process.     

Zur Kristallstruktur von Ba3In2O6

About the Crystal Structure of Ba₃In₂O₆ Single crystals of Ba₃In₂O₆ could be prepared by recrystallization of a flux and by solid state reaction in closed platinium tubes, respectively. Ba₃In₂O₆ crystallizes with tetragonal symmetry (space group 14/mmm, a = 4.1868; c = 21.7041 Å, Z = 2). Single crystal X-ray work lead to a crystal structure like La_2-xSr_1+xCu₂O_6-δ therefor Ba₃In₂O₆ is a modified member of the Sr₃Ti₂O₇-Type. The coordinations of Ba²⁺ and In³⁺ are described and the relations to the Sr₃Ti₂O₇-type are discussed.     

Ferromagnetic and dielectric properties of lead free KNbO3-CoFe2O4 composites

Multiferroic (1-x)KNbO₃-(x)CoFe₂O₄ (x = 0.0, 0.25, 0.5, 0.75 and 1.0 mol) composites were prepared by solid state reaction method. X-ray diffraction results showed that the prepared (1-x)KNbO₃-(x)CoFe₂O₄ composites belong to orthorhombic system for x = 0.0 (perovskite KNbO₃), cubic system for x = 1.0 (spinel CoFe₂O₄) and mixed phase of KNbO₃ and CoFe₂O₄ for x = 0.25, 0.5 and 0.75. Nb-O and Fe-O stretching vibrational modes were observed in the Fourier transform and Raman spectral analyses, respectively. The HR-SEM analysis showed that the morphology of KNbO₃ and CoFe₂O₄ composites was significantly modified by CoFe₂O₄ content. Energy dispersive X-ray spectroscopy results confirmed the presence of K, Nb, Fe, Co and O in (1-x)KNbO₃-(x)CoFe₂O₄ composites. The ionic state of Nb, Co, Fe and O was examined by X-ray photoelectron spectroscopy analysis. The high value of coercivity (H_c = ∼981Oe) for x = 0.5 and the enhanced dielectric constant for x = 0.5 and 0.75 were observed.     

Estimation of average heat capacities of condensed phase transformation products in the Y−Ba−Cu−O system

A method of calculation of average heat capacities of phase transformation products of complex oxides is suggested. The method takes into account the physical state of products and the increase in the heat capacities of products due to the change of entropy at a phase transformation. Average heat capacities of products formed in a congruous melting of compounds (YCuO₂ and Y₄Ba₃O₉), in an incongruous melting of compounds (Y₂Cu₂O₅, BaCuO₂, BaCu₂O₂, Y₂BaCuO₅, YBa₂Cu₃O₇, YBa₂Cu₃O₆) and in a decomposition in a crystalline state of compounds (Y₂BaO₄, Y₂Ba₂O₅, Y₂Ba₄O₇, Ba₂CuO₃, Ba₃Cu₅O₈, YBa₂Cu_3.5O_7.5, YBa₂Cu₄O₈, YBa₂Cu₅O₉) was estimated by using three methods.