BaO CuO Research Articles

Low-temperature growth conditions of YBa 2Cu 3O 7− δ using Ba–Cu–Ag–O–F solvent

Growth temperature of YBa 2Cu 3O 7− δ grown from the solvent which is composed of BaO–CuO–Ag–BaF 2 have been investigated in order to find the lowest temperature of the processing temperature. BaF 2 and Ag containing solvent of BaO–CuO whose molar ratio of Ba/Cu=30/70 can grow YBCO crystals at 805°C under the atmosphere of low oxygen partial pressure. The oxygenated crystals grown at 820°C show superconductivity at 92 K. Crystalline films grown on oxide and metal substrates show critical current density of about 1 MA/cm 2 and 1-cm width critical current over 50 A/cm at 77 K.

Ternary phase diagram of SmO 1.5–BaO–CuO y system for melt processing

The quasi-ternary SmO 1.5–BaO–CuO y phase diagram in air near CuO-rich corner was experimentally constructed at the temperature range of 975–1030°C. The solubility lines of Sm in Ba–Cu–O solutions with Ba/Cu ratio of 0.6/0.33 were determined. It has been found that both x in Sm 1+ x Ba 2− x Cu 3O z solid solutions (Sm123) and the width of the Sm123 primary crystallization field increases with decreasing temperature. The maximum substitution content of x=0.75 was obtained at 975°C. From the tie lines feature it could be possible to grow Sm123 with a small substitution ratio using solutions with Ba/Cu⩾0.6 in air.

TEM of ultra-thin DyBa 2Cu 3O 7–x films deposited on TiO 2 terminated SrTiO 3

Using pulsed laser deposition ultra-thin DyBa 2Cu 3O 7– x films were deposited on a single terminated (0 0 1) SrTiO 3 substrate. The initial growth was studied by high-resolution electron microscopy. Two different types of interface arrangements occur and were determined as: bulk–SrO–TiO 2–BaO–CuO–BaO–CuO 2–Dy–CuO 2–BaO–bulk and bulk–SrO–TiO 2–BaO–CuO 2–Dy–CuO 2–BaO–CuO–BaO–bulk. This variable growth sequence causes structural shifts, resulting in antiphase boundaries with displacement vector R=[0 0 1 3 ] , as well as local chemical variations.

Carbon incorporated YBa 2Cu 3O 7−d crystal; growth, phase separation and enhancement of irreversibility field

Carbon incorporated YBa 2Cu 3O 7−d (YBCO) crystalline films have been grown from a high temperature solution of BaOCuO containing barium carbonate. Superconducting properties of YBCO crystal containing carbon have been measured. Transition temperature significantly decreases from about 90K both in transport and magnetic measurements when the carbon content exceeds 0.06wt%. Hysteresis loop has a peak at 1–2T for the sample with the carbon concentration of 0.045wt%. The irreversibility field increases as the carbon concentration decrease.

Study of the rate-limiting processes in liquid-phase epitaxy of thick YBaCuO films

Liquid-phase epitaxy was used to grow c-axis YBa 2Cu 3O 7−δ thick films on NdGaO 3 (1 1 0) substrates in an Y supersaturated BaO–CuO solvent. In the case of stationary substrates, the familiar √ t growth kinetics is found. Substrate rotation was employed in order to induce forced convection in the liquid, thereby reducing the thickness of the diffusion boundary layer. The resulting growth kinetics showed transient and steady-state growth regimes. The transient regime extends to about 200 s with √ t growth kinetics. In the steady-state regime, diffusion across an established diffusion boundary layer led to a linear increase of film thickness with time. This diffusion boundary layer was estimated to be ∼35 μm for a substrate rotating at 200 rpm. Detailed study of the film growth suggested the presence of an interface kinetics that limited the growth on a competitive basis with volume diffusion in the liquid. The phenomenological kinetic coefficient is found to be ∼2.5×10 −6 m s −1, which is significantly higher than theoretically predicted. The diffusion coefficient of Y in the solution was estimated from viscosity (Stokes–Einstein and Sutherland relations) to be around 2.9–4.3×10 −10 m 2 s −1 at 990°C, while the growth data gave a value of ∼4×10 −10 m 2 s −1.

Initial growth mechanism of YBCO films in liquid phase epitaxy process

The initial stage of growth for YBa 2Cu 3O x (Y123) films on (100) MgO substrates by liquid phase epitaxy (LPE) was investigated. In the initial stage, Y123 seed films partially dissolved into BaO–CuO solution, and Y123 islands were epitaxially grown from the undissolved seed grains on an MgO substrate within 1 s. It was found by XRD analysis that the LPE films with grain orientation of fourfold symmetry on the surface of MgO substrate were grown from not only a fourfold symmetrical seed film but also an eightfold symmetrical one. This phenomenon cannot be fully explained by the coarsening mechanism due to the curvature difference. The difference in the interface energies between Y123 and MgO should be considered to understand the preferential dissolution and growth.

Effect of oxygen partial pressure on quasi-ternary phase diagram of NdO 1.5–BaO–CuO system

Quasi-ternary phase diagrams of the NdO 1.5–BaO–CuO system under low and high oxygen partial pressure atmospheres ( P O 2 =0.01, 1.00 atm) were constructed. Liquidus curves, solidus lines, and the equilibrium tie-lines in the two-phase field of liquid and Nd 1+ x Ba 2− x Cu 3O 6+ δ were determined experimentally. As the oxygen partial pressure of atmosphere increased, liquidus curves were shifted to the Nd-rich region and the Nd solubility in the solvent with lower BaO/CuO ratio was further increased. The stable region of Nd 1+ x Ba 2− x Cu 3O 6+ δ , which was under the influence of temperature and P O 2 , was widened at lower temperature and/or higher P O 2 . Especially, its sensitivity to P O 2 was high. By investigating equilibrium tie-lines, the x value of Nd 1+ x Ba 2− x Cu 3O 6+ δ was reduced and became insensitive to the BaO/CuO ratio of liquid phase equilibrated with Nd 1+ x Ba 2− x Cu 3O 6+ δ as the BaO/CuO ratio increased and slightly reduced as temperature decreased. Those tendencies were maintained at different P O 2 . It was discussed thermodynamically why NdBa 2Cu 3O 6+ δ (Nd123) superconductors, fabricated in a reduced oxygen atmosphere, show high superconductive critical temperature. One of the reasons for this phenomenon was the decrease of the solubility of Nd 1+ x Ba 2− x Cu 3O 6+ δ with the oxygen partial pressure of atmosphere.

Phase transition and superconductivity of (Ba,Sr,La) 2YCu 3O z ( z>6.9)

A series of (Ba,Sr,La) 2YCu 3O z ( z>6.9) samples is studied to elucidate the relationship between structure, cation composition and oxygen content. The concentration of La plays an important role in the orthorhombic to tetragonal phase transition. The tetragonal structure is stabilized by increasing oxygen content and decreasing average ionic radius of cations on the Ba site. The phase transition is explained in terms of the random distribution of CuO 5 pyramids in the BaO–CuO x slab. Superconductivity does not depend significantly on the phase transition.

Cation disorder in superconducting HgBa 2CaCu 2O 6+ δ films prepared on SrTiO 3 substrates

Hg–Ba–Ca–Cu–O thin films prepared on SrTiO 3 (100) substrates generally exhibit shorter c-axis unit cell lengths and lower zero-resistance superconducting transition temperatures as compared to bulk. Microstructural studies of HgBa 2CaCu 2O 6+ δ films based on X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) revealed shorter BaO–CuO 2 interplanar distances and longer CuO 2–CuO 2 average distances as compared to those reported for bulk compounds. It is suggested that the observed cationic disorder causes smaller c-axis lattice parameter and is probably induced by the lattice mismatch between film and substrate. The observed atomic rearrangements are expected to influence superconducting properties of the Hg-based films.

Morphology and etching studies on YBCO and CuO single crystals

Single crystals of YBCO (Y123) and CuO have been grown from a BaO–CuO (28:72) flux using a low axial gradient furnace (∼1°C/cm). Growth morphology of the grown crystals was studied using an optical microscope, scanning electron microscopy and atomic force microscopy. Cell parameter values and chemical composition of the grown crystals were determined from the X-ray diffraction data and inductively coupled plasma analysis, respectively. Etching studies were done for both the crystals using different etchants. Oxygen stoichiometry of the YBCO crystal was determined by iodometry titration analysis.

Investigations on nucleation thermodynamical parameters of NdBa 2Cu 3O 7- δ (Nd123) crystallizing from high temperature solution

Theoretical investigations have been made to calculate the nucleation thermodynamical parameters like interfacial energy between the solid Nd123 and its flux BaO–CuO, metastable zone-width, volume free energy, critical energy barrier for nucleation and radius of critical nucleus from the knowledge of solubility data and by applying the classical nucleation theory. Results are discussed to understand the growth kinetics of Nd123 crystals from a high temperature solution.

PHASE DIAGRAM, CRYSTAL GROWTH AND SUPERCONDUCTIVITY OF CALABACU3O7-Y CRYSTAL

CaLaBaCu3O7−y (CLBCO) is a high Tc superconductor with unique tetragonal structure and cross-cationic substitution sites. In this paper, we present our study on the BaO—CuO—CLBCO phase diagram and its application to the crystal growth of CLBCO. The eutectic composition of BaO—CuO system is confirmed by the improved thermogravimetric analysis 〈ITGA〉 and is used for the crystal growth as a self-flux system. A pseudo-phase diagram of CLBCO—eutectic flux system is established by differential thermal analysis 〈DTA〉 which enables the selection of a suitable starting composition and temperature program for the crystal growth. We explore the relation between crystal growth, cell parameters and the main superconducting transition temperatures Tc. The Tc of CLBCO crystals depends strongly on the Ca/La ratio in the starting materials. As for YBa2Cu3O7−y 〈YBCO〉, a small amount of BaF2 additive greatly increases the main transition temperature of CLBCO crystals. This can be understood by the cluster model we proposed previously for YBCO crystal growth. Based on the research on the phase diagram, crystal growth and the superconductivity, high Tc crystals of CLBCO with size up to 6.5 × 6.5 × 0.43 have been grown from the eutectic self-flux system with BaF2 as additive. Tc was determined by an a.c. susceptibility measurement, which shows the main transition temperature up to 60 K for the as-grown crystals. After annealing in flowing oxygen at 600 to 400 °C for two days, Tc increased to 73 K.

ChemInform Abstract: Construction of the Quasi‐Ternary Phase Diagram in the NdO1.5—BaO—CuOx System in an Air Atmosphere. Part 1. Equilibrium Tie Lines in the Nd1+xBa2‐xCu3O6+δ (Nd 123) Solid Solution and Liquid Region.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

New type 2212 structure discovered in Tl–Hg–Ba–Cu–O system

A new type 2212 phase is discovered in a Tl–Hg–Ba–Cu–O sample, in which the M site, located in the so-called infinite-layer block of CuO 2/M/CuO 2, is occupied by (Tl,Hg) rather than AE/Y/RE elements (AE: alkaline earth elements; RE: rare earth elements). By transmission electron microscope studies, it is found that this phase has a space group of I4/mmm and the lattice parameters of a=3.88 Å and c=29.1 (3) Å. The atomic ratio determined by energy dispersive X-ray analysis is Tl:Hg:Ba:Cu=25.14:13.74:31.40:29.72. High resolution transmission electron microscope observations and simulations revealed that this phase has a so-called 2212 structure and a stacking order of {(Tl,Hg)O 1− δ –BaO–CuO 2–(Tl,Hg)–CuO 2–BaO–(Tl,Hg)O 1− δ }.

Growth of high quality YBCO single crystals using BaZrO 3 crucibles

High density BaZrO 3 ceramic crucibles have been successfully fabricated and used to grow high quality YBa 2Cu 3O 7− x (YBCO) single crystals by the BaO–CuO self flux method. The ceramic crucibles are inert and insoluble in the Y 2O 3–BaO–CuO melt, have a long lifetime, and can be used repeatedly for crystal growth runs. The crystals grown using the crucibles have not only high chemical purity (99.99–99.995%), but also a high degree of crystalline perfection as characterized by an extremely sharp X-ray rocking curve (FWHM=0.007°), very weak magnetic flux pinning and a magnetic irreversibility line that lies about 20 K below the line for the best YSZ crucible grown crystals.

Thermochemistry of 1 : 2 : 4 phases in the Ho 2O 3–CuO–BaO, Dy 2O 3–CuO–BaO systems

Thermochemical investigations of 1 : 2 : 4 phases in the Ho(Dy)–Ba–Cu–O systems were performed by solution calorimetry in 6 N HCl at 323 K. On the basis of direct dissolution enthalpies of Ho 2O 3, Dy 2O 3, BaCO 3, HoBa 2Cu 4O 8, DyBa 2Cu 4O 8 and CuO thermodynamic data were obtained for the formation of 1 : 2 : 4 phases: 1 – from the oxides; 2 – from the mixture including BaCuO 2; and 3 – from the mixture including BaCO 3. The data obtained showed that the abovementioned phases were thermodynamically stable with respect to the mixture with BaCuO 2, namely, with respect to the reaction: 1/2Ln 2O 3+2CuO+2BaCuO 2+1/4O 2=LnBa 2Cu 4O 8.

NdBa 2Cu 3O 7− δ stoichiometry control (at pO 2=0.21 atm) and enhancement of superconductivity

In the air atmosphere, high superconducting transition temperature ( T c) Nd 1+ x Ba 2− x Cu 3O 7− δ (NdBCO) single crystals were grown by top-seeded solution-growth (TSSG). Two controllable thermodynamical parameters, i.e. liquid composition and growth temperature were focused on. Using the ratio of Ba to Cu (Ba:Cu) at 0.78 in the liquid, the grown NdBCO crystal displays onset T c of 94.6 K with a sharp transition width Δ T less than 1.5 K. The Ba-rich liquid leads to the lower substitution of Ba with Nd in grown crystals, resulting in the higher T c. This finding suggests that the Ba:Cu ratio in the liquid is a very important processing parameter for obtaining higher T c of the NdBCO superconductors. In addition, the higher T c as well as the lower Nd substitution can be achieved when using the lower growth temperature. These results are consistently interpreted by the NdO 1.5–BaO–CuO ternary phase diagram.

The influence of CuOBaO mixture addition on the grain growth and dielectric characteristics of BaTiO 3 ceramics

Densification, grain growth, and dielectric characteristics of BaTiO 3 during liquid-phase sintering of BaTiO 3 ceramics was investigated for CuOBaO (molar ratio, CuO BaO = 1, 2, and 2.5 ) mixture addition. Sintering in air for 1 to 16 h at 950 to 1250 °C was studied. The grain growth for CuO-BaO mixtures fluxed BaTiO 3 was analysed from the kinetic growth equation: G n = kot ∗exp(− Q/ RT). The average grain growth exponents are about 5.3, 5, and 4.3 and grain growth activation energy are 290 ± 60, 314 ± 40, and 348 ± 19 kJ mol −1 for BaTiO 3 fluxed with CuO BaO = 1, 2, and 2.5 , respectively. For the same sintering condition as the CuO BaO ratio increases, the maximum dielectric constant (revealed at Tc) increases, the tetragonal-cubic phase transition (Tc) is shifted to lower temperature, and the orthorhomic-tetragonal phase transition is moved to higher temperature.

EFFECT OF CUO-BAO MIXTURE CONTENT ON THE GRAIN GROWTH OF BATIO3

The present work has been aimed at studying the effect of processing variables such as amount of additions, sintering temperature, and duration on the density, microstructure, and grain growth of BaTiO3/CuO–BaO ceramics. Grain growth of BaTiO3 during liquid-phase sintering is investigated for CuO–BaO (mole ratio, CuO/BaO=2.5) mixture additions from 0.5 wt% to 2 wt%. Sintering in air for 1 to 16 h at 950 °C to 1250 °C is studied. BaTiO3 with 0.5 wt%, 1 wt%, 1.5 wt%, and 2 wt% CuO–BaO mixture additions, the average grain growth exponents are 5.3, 4.3, 5.9, and 9.2 and the activation energies are 605±60, 348±19, 650±50, and 810±110 kJ mol-1, respectively. For all compositions, the grain growth exponents decrease with increasing sintering temperature. © 1998 Chapman & Hall

Equilibrium tie-line in PrOy–BaO–CuO ternary phase diagram around peritectic temperature of Pr1+xBa2−xCu3O7−δ

This paper presents tie-lines between Pr1+xBa2−xCu3O7−δ and liquid on a PrOy –BaO–CuO ternary phase diagram at 965, 970, 975, 980, and 990 °C in air atmosphere, for which knowledge is necessary to fabricate composition controlled Pr1+xBa2−xCu3O7−δ single crystals by the solution growth method. Liquidus faces have been investigated by dipping MgO single crystal rods into the thermal equilibrium melt at various temperatures and analyzing the composition of the adhering melt by ICP. The compositions of Pr1+xBa2−xCu3O7−δ solid solution coexisting with various compositions of liquids were obtained by quantitative EPMA analysis of quenched melts. Tie-lines were calculated by applying the lever rule to these experimental data for solid compositions and liquidus faces. Furthermore, the relationships between solid solubilities and peritectic temperatures of Pr1+xBa2−xCu3O7−δ are reported.