CuO Flux Research Articles

Effect of Bi2O3-CuO Flux on the Microstructure, Soft Magnetic Properties, and Gyromagnetic Properties of NiCuZn Ferrites for LTCC Devices.

In this work, the electromagnetic properties of Ni0.22Cu0.31Zn0.47Fe2O4 (NiCuZn) ferrites doped with 0.3 wt% Bi2O3 + xCuO flux (x = 0.2, 0.4, 0.6, and 0.8 wt%) were studied. Doping resulted in a reduction in the sintering temperature to 900 °C. The doped ferrites were synthesized via the solid-state method. XRD patterns revealed that the prepared ferrites had a cubic spinel structure; thus, a moderate addition of flux did not change the crystal structure. The SEM images, as well as the density and grain size distribution of the samples, showed that the NiCuZn ferrites had densified, homogenized, and contained fully grown grains for x = 0.6 wt%. The sample exhibited good soft magnetic properties, with μ' reaching the maximum value of 245.4 for x = 0.6 wt% and ε', Ms, and Hc reaching the maximum values of 23.1, 28.06 emu/g, and 45.86 Oe for x = 0.8 wt%, respectively. Furthermore, the ferrites exhibited good gyromagnetic properties, with 4πMs reaching the maximum value of 1744 Gauss for x = 0.8 wt% and ΔH reaching the minimum value of 228 Oe for x = 0.6 wt%. NiCuZn ferrites were successfully sintered at a lower temperature (900 °C) by adding Bi2O3-CuO flux through LTCC technology and exhibited good soft magnetic properties and gyromagnetic properties. We envisage that these ferrites could be used in multilayer devices.

Low-temperature sintering of Ba(Zr,Y)O3-based proton conducting oxides using BaO–CuO eutectic flux as sintering aid

The major barrier to the practical application of Ba(Zr,Y)O3 (BZY) as an electrolyte material for proton-conducting fuel cells (PCFCs) lies in its extremely inferior sintering characteristics. In this research, flux composed of 28mol% BaO and 72mol% CuO was employed as a novel sintering aid for BZY. Incorporation of nano-crystalline BaO–CuO flux, with a eutectic point of 890°C, remarkably enhanced the sintering behavior of BZY due to the formation of a transient liquid phase, and a relative density of up to 97% of the theoretical density was obtained at 1300°C with a short soaking time of 2h.

Dielectric and piezoelectric properties of low-temperature sintered lead zirconate titanate ceramics with 0.78PbO-0.22CuO flux addition

Liquid phase sintering of lead zirconate titanate (abbreviated as PZT) ceramics with a 0.78 PbO-0.22 CuO (10:1 in weight ratio) flux was investigated. A small amount sintering flux consisting of a stoichiometrically mixed oxide of PbO-CuO with a eutectic composition successfully accelerated densification of the PZT ceramics far below the conventional sintering temperature. With the 3 wt% flux additions, full densifications of the PZT ceramics were achieved at temperatures as low as 825 °C. The results obtained in the crystal structure, microstructure, and electrical property analyses suggest that the Cu2+ impurity ion substitutes as an acceptor center for the perovskite B-site without forming isolated secondary phases. Defect associates of the Cu2+ impurities and charge compensating oxygen vacancies appear to affect dielectric and piezoelectric properties of the sintered PZT samples in both positive and negative ways by forming defect dipoles. When the Cu2+ content is small, slightly improved dielectric and piezoelectric performances were achieved, though ferroelectric relaxation was obviously developed at the higher Cu2+ contents. For the PZT samples sintered at 825 °C with 3 wt% flux addition, relative dielectric permittivity was 2200 and dielectric loss was less than 2%. Remnant polarization, coercive fields, and piezoelectric coefficient (d33) were 32 μC/cm2, 8.9 kV/cm and 373 pC/N, respectively.

Local structures and roles of Fe3+ and Cr3+ in p‐type semiconductor CuAlO2

AbstractSingle crystals of the p‐type semiconductor CuAlO2, synthesized from the CuO flux method, have been investigated by electron paramagnetic resonance (EPR) spectroscopy at temperatures from 3.5 to 294 K. EPR spectra reveal an axial Cr3+ center and an axial Fe3+ center, presumably arising from impurities in the starting materials. The Cr3+ center at 294 K is characterized by g = 1.979(1) and D = − 7803(3) × 10−4 cm−1. The Fe3+ center at 294 K has g// = 1.9942(1), g⟂ = 1.9964(1), D = 261.9(3) × 10−4 cm−1, $B_{4}^{0} = 4.533(3) \times 10^{- 4} \,{\rm cm}^{- 1} $, and $B_{4}^{3} = 104.23(3) \times 10^{- 4} \,{\rm cm}^{- 1} $. These spin‐Hamiltonian parameters, evaluated by superposition model analyses and periodic density functional theory (DFT) calculations, suggest that both Cr3+ and Fe3+ occupy the Al3+ site but the latter involves distortion related to perturbation from a substitutional Cu+ ion at the nearest Al site. This difference in the local structure between Fe3+ and Cr3+ explains their contrasting effects on the p‐type conductivity in CuAlO2.

Liquid phase epitaxy growth of Ln–Ba–Cu–O (Ln=Yb, Er, Pr) films using BaZrO 3 crucibles

Ln–Ba–Cu–O (LnBCO) (Ln=Yb, Er, and Pr) films have been grown on NdGaO 3(1 1 0) by liquid phase epitaxy technique using BaZrO 3 crucibles. YbBCO films have epitaxially grown at temperatures ranging from 940 to 899 °C. The YbBCO films grown at 940 and 899 °C showed c-axis and a-axis orientations, respectively. The YbBCO films annealed in oxygen showed T c(onset) of 88–92 K. ErBCO films have grown at temperatures ranging from 999 to 938 °C, and showed T c(onset) of approximately 95 K being after annealed in oxygen. For the growth of PrBCO films, BaCuO 2–CuO flux with Ba/Cu ratios of 4/5, 3/5, and 3/7 was used. The PrBCO films with a-axis orientation have grown at temperatures ranging from 1011 to 974 °C. The annealed PrBCO films showed semiconducting behavior on R– T curves, and no superconducting transition over 77 K. The contamination of impurities to the films from the BaZrO 3 crucible was not observed by EPMA analysis.

Studies on the growth aspects of superconducting Eu 1.5Ce 0.5Sr 2Cu 2TiO 10− δ (Ti-1222) single crystals

Single crystals of superconducting Eu 1.5Ce 0.5Sr 2Cu 2TiO 10− δ (Ti-1222) have been grown from excess CuO and SrCO 3–CuO mixed fluxes by slow cooling technique. The growth temperature was determined by studying the thermal behaviour of polycrystalline Eu 1.5Ce 0.5Sr 2Cu 2TiO 10− δ with different fluxing agents. Morphology studies by SEM reveals the layer growth pattern, indicative 2D nucleation mechanism. Stoichiometric Ti-1222 crystals were obtained for CuO flux, whereas composition of SrCO 3–CuO mixed flux is different from the starting composition. Ti-1222 crystals possess tetragonal structure with a superconducting transition at 22 K. Growth aspects and phase formation of Ti-1222 for both CuO and SrCO 3–CuO flux systems have been studied in detail.

Surface studies of twinned of YBa 2Cu 3O 7−δ crystals

Single crystals of YBa 2Cu 3O 7−δ have been grown from BaO - CuO flux. Surface studies of the oxidised crystals were done using optical polarizing microscope, scanning tunnelling (STM) and atomic force microscopy (AFM). Ferroelastic properties of YBa 2Cu 3O 7−δ crystals give a possibility to interpret twins within the framework of the quasidislocation theory. Analysis of this theoretical description gave an idea for investigating morphology of the twinned surface using STM and AFM microscopy. As the result for the first time it was possible to observe by AFM the twin boundaries as convexities of the twinned surface.

Studies on the growth aspects of Eu 1.4Ce 0.6NbSr 2Cu 2O 10−δ single crystals

Growth of Eu 1.4Ce 0.6NbSr 2Cu 2O 10−δ (Nb-2122) single crystals has been investigated. The crystals were grown from excess CuO flux by a slow cooling technique. The crystallization temperature of Nb-2122 compound was determined from DTA to be 1033°C. Laue and powder X-ray diffraction studies confirm the single crystallinity and tetragonal structure of the crystals respectively. The morphologies of the crystals were analysed by SEM.

Crystal growth and characterization of the 4-leg spin ladder compound La 2Cu 2O 5

Crystallization of La 2Cu 2O 5 has been investigated in the La 2O 3–CuO system for various starting compositions both in air and oxygen atmospheres. In air, we find that there exists a new region of crystallization of La 8Cu 7O 19 phase, just above that of La 2Cu 2O 5. However, this region vanishes completely in flowing-oxygen atmosphere. By utilizing this, large single crystals of the 4-leg spin-ladder compound La 2Cu 2O 5 have been successfully grown from CuO flux by the slow cooling method. Room-temperature resistivity parallel to the ladder direction (‖ b) of the as-grown crystals is estimated to be 1.7×10 3 Ω cm. A significant decrease in the resistivity (798 mΩ cm at 300 K) is observed upon hole doping by means of high oxygen pressure annealing (approximately 400 atm) using a hot isostatic pressing furnace. However, no transition was observed from the semiconducting behavior.

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.

Optimum crucible material for growth of Pr 2− xCe xCuO 4 crystal

With the aim of finding an optimum crucible for growth of Pr 2− x Ce x CuO 4 crystal, reactions between CuO flux and various crucible materials were studied. Among six different crucible materials, Pt, Al 2O 3, ZrO 2, Y 2O 3, CeO 2 and MgO, Pt crucible was suitable for using Ce free solution. For Ce doped solution, MgO crucible was better than other materials. The reactant between Pt crucible and CuO flux was identified as Pt 2Cu. In the case of MgO crucible, Mg 2CuO x and (Mg,Cu)O x were produced as reactants. We found a method to restrain the reaction between the crucible and the solution. Using this method for growth of Ce doped crystal, we grew a crystal of size 30 mm∅×1.5 mm.

Single-crystal growth and characterization of Zn- and Ni-substituted YBa 2Cu 4O 8

Single crystals of Zn- and Ni-substituted YBa 2Cu 4O 8 with T c=80–20 K for Zn and T c=80–0 K for Ni have been grown from a BaO–CuO flux at 1090°C under 600 bar of O 2. Crystals grown in yttrium stabilized ZrO 2 crucibles do not show contamination from the crucible material. The effective distribution coefficients for Zn and Ni are 0.3 and 1, respectively. The solubility limits are around 2% for Zn and above 6.5% for Ni. Single-crystal X-ray diffraction is used to characterize the crystal quality but it lacks the sensitivity to conclusively differentiate the site preference for small amounts of substituted ions. All crystals show sharp superconducting transitions with Δ T c gradually increasing with decreasing T c.

Liquid phase epitaxy of crystalline REBa 2Cu 3O 6+δ films on reactive substrates using the BaF 2BaOCuO flux

Phase relations concerning the crystal formation of YBa 2Cu 3O 6+δ and NdBa 2Cu 3O 6+δ phases from the BaF 2BaOCuO flux have been investigated by the liquid phase epitaxial technique on various substrates. As the amount of BaF 2 in the solution increases, the temperature of REBa 2Cu 3O 6+δ (RE = Y, Nd) formation decreases down to about 920°C not only in the Y system but also in the Nd system. The decrease of the growth temperature allows us to form liquid phase epitaxial thick films on the reactive substrates such as yttria-stabilized zirconia and SrTiO 3, which rapidly react with REBa 2Cu 3O 6+δ and the melt of barium cuprate flux at high temperatures. Our studies have also revealed that the seed layer pre-deposited on the substrates plays an important role in epitaxial growth of REBa 2Cu 3O 6+δ to form thick films on these substrates.

Growth mechanisms of YBa 2Cu 3O 7− δ single crystals grown by the flux method using alumina crucibles

The growth behaviour of large, thin, plate-like and almost cubic YBa 2Cu 3O 7− δ single crystals grown from high temperature solution (BaOCuO flux) using alumina crucibles was studied by optical microscopy. Growth spirals of various shapes were observed on both {001} and {100} surfaces while surface dendrites and hopper morphology were also observed on {100} {010} surfaces. Both the dislocation growth and two-dimensional growth mechanisms have been used to interpret the observed features, with the dislocation growth mechanism being found responsible for the formation of the {001} surfaces, and the two-dimensional growth mechanism being responsible for the formation of the lateral {100} {010} surfaces. The reason for this difference in the growth mechanisms for the two types of surfaces is considered to arise from the anistropic crystal structure.

Raman and weak ferromagnetism in Eu 2CuO 4

We show that there is a subtle instability of the T′ structure for the R 2CuO 4 (R = rare earth) compounds at the center of the R series with the boundary at R = Eu. Crystals grown in Pt crucibles and PbO flux show weak ferromagnetism (WF) and two temperature-dependent forbidden Raman peaks. Crystals grown in alumina crucibles and CuO flux do not show WF and the forbidden Raman peaks are much weaker. The WF and forbidden Raman peaks in Eu 2CuO 4 suggests that the instability of the T′ structure is associated with O(1) displacement in the CuO 2 planes.

Raman-scattering and weak-ferromagnetism studies in Eu2CuO4.

We show that there is a subtle instability of the ${\mathit{T}}^{\ensuremath{'}}$ structure for the ${\mathit{R}}_{2}$${\mathrm{CuO}}_{4}$ (R=rare earth) compounds at the center of the R series with the boundary at ${\mathrm{Eu}}_{2}$${\mathrm{CuO}}_{4}$. Crystals grown in Pt crucibles and PbO flux show weak ferromagnetism (WF) and two strongly temperature-dependent forbidden Raman peaks. However crystals grown in alumina crucibles and CuO flux do not show WF and the forbidden Raman peaks are much less intense. The observation of WF and forbidden Raman peaks for ${\mathrm{Eu}}_{2}$${\mathrm{CuO}}_{4}$ compounds suggests that the instability of the ${\mathit{T}}^{\ensuremath{'}}$ structure may be associated with O(1) displacement in the ${\mathrm{CuO}}_{2}$ planes. \textcopyright{} 1996 The American Physical Society.

Single-crystal growth and characterization of the Pb0.5Sr2.5Y1−xCaxCu2Oy system

Two kinds of methods such as spontaneous nucleation from flux-free stoichiometric melt and CuO flux method have been used for the growth of Pb0.5Sr2.5Y1−xCaxCu2Oy single crystals. The morphologies, phases, and compositions occurring in the crystals grown from the two kinds of methods were compared systematically. Optimum conditions for the growth of larger 1212 phase single crystals are x =0.15, 0.25, and 0.35. The lattice parameters of the crystals with the 1212 phase were found to be increasing upon Ca doping. The resistivity behavior of the PbSrYCaCuO single crystals with the 1212 phase both in the state of as-grown and after extended annealings under various oxygen partial pressure was also discussed briefly.

Synthesis, transport, and magnetic properties of Ln 2− xCe xCuO 4− y single crystals (Ln = Nd, Pr, Sm)

Single crystals Ln 2- x Ce x CuO 4- y (Ln = Nd, Pr, Sm; 0⩽ x⩽0.2) were grown in CuO flux and characterized by means of X-ray diffraction and microprobe analysis, electrical resistivity, and magnetic susceptibility. There is a large variation of the Ce content from crystal to crystal within a given batch and the distribution width decreases with increasing Ce starting composition. The temperature dependence of the normal-state electrical resistivity determined superconducting critical temperature T c are very sensitive to the heat treatment. The magnetic susceptibility of Ln 2- x Ce x CuO 4- y single crystals, measured f or two orientations of the crystals with respect to the applied field H, reveals a high anisotropy and indicates the presence of crystalline electric-field (CEF) effects.

Growth of large size single crystals and whiskers of Bi2Sr2CaCu2O8 by step-cooling method

Single crystals of large surface area with dimensions of 10×3×0.2 mm3 have been grown from excess CuO flux by adopting a step-cooling method. Crystals have also been grown from a stoichiometric melt and are thicker and smaller in size (2×1.5×0.5 mm3). Laue and powder X-ray diffraction studies confirm the single crystallinity and orthorhombic structure of the crystals, respectively. Single crystalline whiskers of length 4–6 mm, which are highly deficient in Sr and Ca, and platelet crystals of the Ca-free phase have also been observed for excess CuO flux. AC susceptibility studies show superconducting transition of about 82 and 78 K for crystals grown from CuO flux and stoichiometric melt, respectively.

Iron stabilization of the 2223 PbBiSrCaCuO superconducting phase

Complete stabilization of crystals of the high- T c superconducting oxide (PbBi) 2Sr 2Ca 2Cu 3O 10, which is characterized by a T c of 110 K and space group of A2aa, has been achieved by synthesizing the material in an FeO-doped CuO flux. The resulting crystals formed with a chemically inert FeO surface layer appear resistant to further etching or degradation at room temperature and atmosphere.