By electron-beam (e-beam) melting, we prepared 0.4 wt% carbon-infused copper (CuCv4), and a copper control without carbon addition (CuCv0). Scanning electron microscopy and helium ion microscopy (HIM) were performed on the as-solidified surface, fracture surface, and ion-polished surface of the CuCv4 sample. The results revealed that graphitic carbon flakes cover the as-solidified surface, and carbon nanoparticles and clusters exist in the fracture and ion-polished surfaces. HIM on the ion-polished surface revealed a unique ripple-shaped feature, which is possibly associated with the infusion of carbon nanoribbons in the copper matrix. The bulk densities were measured to be 8.86 and 8.53 g/cm3, which correspond to relative densities of 98.9% and 96.4% for the CuCv0 and CuCv4 samples, respectively. In addition, apparent electrical conductivities were measured to be 56.9 and 57.5 MS/m, respectively, for the e-beam melted CuCv0 and CuCv4 samples. These values correspond to true electrical conductivities of 100.5% IACS (International Annealed Copper Standard) and 107.4% IACS after correction for the porosity. Our results reveal remarkable promise of using covetic copper for the next generation conductors in energy applications from microelectronic devices to high-power transmission cables.

Bulk samples of a novel cermet (ceramic/metal composite) hydrogen transport membrane (HTM) were subjected to thermal cycling in the temperature range between 25-850°C to study phase transformations and microstructural changes under thermal shock. Scanning electron microscopy (SEM) and electron probe micro analyzer (EPMA) with energy dispersive spectroscopy (EDS) were used to characterize the microstructural and chemical changes in the membrane upon thermal cycling. SEM & EPMA analyses indicated that the temperature gradient during thermal cycling produced more micro-cracks inside the HTM disc, whereas, the chemical reaction between Pd and oxygen to form PdO disturbed the continuity of the metal palladium (Pd) - Yttria Stabilized Zirconia (YSZ) dual phases interconnection system from surface down. The agglomerates of un-crystallized YSZ grains found to be the inherent in the cracks of the as-received HTM. A combination of trans-granular and inter-granular crack propagation results around the YSZ grains and the new precipitates. Based on the electron fractography analyses by both SEM and EPMA, the micro voids coalescence develops ahead of the crack tips in the cross-section of the HTM after 500 thermal cycles.

Antiferroelectric (AFE) Pb0.92La0.08Zr0.95Ti0.05O3 (PLZT) films were grown on nickel foils with lanthanum nickel oxide buffer by chemical solution deposition. We observed field-induced AFE-to-ferroelectric (FE) phase transition. The electric field for the AFE-to-FE phase transition (EAF ≈ 270 kV/cm) and that for the reverse phase transition (EFA ≈ 230 kV/cm) were measured at room temperature on samples with PLZT films of ≈1-µm thickness. Relative permittivity of ≈560 and dielectric loss of <0.05 were measured near zero DC bias field. Hysteresis loop analysis showed that energy densities of ≈53 and 37 J/cm3 can be stored and recovered from the film-on-foil capacitors at 25 and 150 °C, respectively. Highly accelerated life tests were conducted. The projected mean time to failure is >5000 h when the capacitors are operated at room temperature with an applied field of ≈300 kV/cm.

Ferroelectric film-on-foil capacitors hold special promise to replace discrete passive components in the development of electronic devices that require greater performance and smaller size. We have grown ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films on nickel substrates by chemical solution deposition. The dielectric properties were determined for samples of ≈1.15-μm-thick PLZT film grown on LaNiO3-buffered nickel substrates. Measurements on these samples yielded a dielectric constant of ≈1300, dielectric loss (tan δ) of ≈0.05, and leakage current density of ≈7 × 10-9 A/cm2. An energy density of ≈74 J/cm3 was measured at room temperature with 250-μm-diameter capacitors. Highly accelerated lifetime tests were conducted at 100°C to determine the reliability of the ≈1.15-μm-thick film-on-foil capacitors under field stress conditions (with applied electric field from 8.7 × 105 V/cm to 1.3 × 106 V/cm). The breakdown behavior of the PLZT film-on-foil capacitors was evaluated by Weibull analysis. A voltage acceleration factor of ≈-6.3 was obtained. From the test results, a mean time to failure of >3000 hr was projected for capacitors operated at 100°C with ≈2.6 × 105 V/cm dc electric field.

Ferroelectric film-on-foil capacitors hold special promise to replace discrete passive components in the development of electronic devices that require greater performance and smaller size. We have deposited Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films on base metal foils to form film-on-foil capacitor sheets that can be embedded into printed circuit boards. The rootmean-square surface roughness was determined to be ≍3 nm for 1.15-μm-thick PLZT films on LaNiO3-buffered Ni foils. The following dielectric properties were measured: relative permittivity of ≍1300 and dielectric loss (tan δ) of ≍0.05, leakage current density of 6.6 × 10−9 A/cm2 at 25°C and 1.4 × 10−8 A/cm2 at 150°C, and mean breakdown strength >2.5 MV/cm. A remnant polarization (Pr) of ≍33 μC/cm2 and coercive field strength (Ec) of ≍50 kV/cm were observed with a maximum voltage of 300 V applied during the P-E loop measurement. The energy storage capability of the dielectric film is ≍45 J/cm3.

Development of electronic devices with higher performance and smaller size requires the passive components to be embedded within a printed wire board (PWB). The “film-on-foil” approach is the most viable method to fabricate suitable passive components. We have deposited high-permittivity thin films of ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) on base metal foils by chemical solution deposition. These capacitors could be embedded into PWBs. However, formation of a parasitic low-permittivity interfacial layer of nickel oxide during thermal processing of the PLZT films considerably reduces the capacitance density. Two approaches were taken to overcome the problem. In the first, a conductive buffer layer of lanthanum nickel oxide (LNO) was inserted between the PLZT film and the nickel foil to hinder the formation of deleterious interfacial oxide. In the second, high temperature processing was done under low oxygen partial pressure such that no interfacial oxide was formed. By these approaches, we have grown high-quality ferroelectric PLZT films on nickel and copper foils. With samples of PLZT grown on LNO-buffered Ni, we measured a dielectric constant of 1300 (at 25°C) and 1800 (at 150°C), leakage current density of 6.6 × 10−9 A/cm2 (at 25°C) and 1.4 × 10−8 A/cm2 (at 150°C), and breakdown field strength >1.2 MV/cm. With samples of PLZT on Cu, we obtained encouraging initial results of dielectric constant >450 and dielectric loss tan(δ) ≈0.04.

Evolution of electronic devices towards higher performance and smaller size requires the passive components to be embedded within a printed wire board (PWB). A “film-on-foil” approach is the most viable fabrication method. A high permittivity of lead lanthanum zirconate titanate (PLZT) thin film was coated on nickel foil by chemical solution deposition. Such a prefabricated capacitor sheet can be embedded into a PWB. However, formation of a parasitic low-permittivity interfacial layer of nickel oxide during thermal processing of the PLZT films considerably reduces the capacitance density. To eliminate this parasitic effect, conductive buffer layer of lanthanum nickel oxide (LNO) was coated by chemical solution deposition on nickel foil. We produced PLZT film-on-foil capacitors with capacitance densities as high as 1.5 μF/cm2 and breakdown field strength >1.4 MV/cm. With the desirable volumetric character, PLZT film-on-foil capacitors hold particular promise for use in high voltage embedded passives.

Mixed-conducting oxides, possessing both ionic and electronic charge carriers, have found wide application in recent years in solid-state electrochemical devices that operate at high temperatures, e.g., solid-oxide fuel cells, batteries, and sensors. These materials also hold promise as dense ceramic membranes that separate gases such as oxygen and hydrogen from mixed-gas streams. We are developing Sr-Fe-Co oxide (SFC) as a membrane that selectively transports oxygen during partial oxidation of methane to syngas (mixture of CO and H2) because of SFC's high combined electronic and ionic conductivities. We have evaluated extruded tubes of SFC for conversion of methane to syngas in a reactor that was operated at ≈900°C. Methane conversion efficiencies were >90%, and some of the reactor tubes were operated for >1000 h. We are also developing dense proton-conducting oxides to separate pure hydrogen from product streams that are generated during methane reforming and coal gasification. Hydrogen selectivity in these membranes is nearly 100%, because they are free of interconnected porosity. Although most studies of hydrogen separation membranes have focused on proton-conducting oxides by themselves, we have developed cermet (i.e., ceramic-metal composite) membranes in which metal powder is mixed with these oxides in order to increase their hydrogen permeability. Using several feed gas mixtures, we measured the nongalvanic hydrogen permeation rate, or flux, for the cermet membranes in the temperature range of 500-900°C. This rate varied linearly with the inverse of membrane thickness. The highest rate, ≈32 cm3(STP)/min-cm2, was measured at 900°C for an ≈15-μm-thick membrane on a porous support structure when 100% H2 at ambient pressure was used as the feed gas.

We have fabricated a solid oxide fuel cell (SOFC) using BaCe0.8Y0.2Ox (BCY) proton conductor as the electrolyte. An ≈ 15-μm-thick dense BCY film was prepared on a porous Ni/BCY cermet (i.e., ceramic/metal composite) substrate by a colloidal spray deposition technique. The gas permeable Ni/BCY cermet substrate backed with nickel mesh was used as the anode, and platinum paste backed with platinum mesh served as cathode. The current-voltage characteristics of the BCY-based SOFC were measured in the temperature range 600-800°C using wet air on the cathode side and wet hydrogen on the anode side. The open circuit voltage was close to the theoretical value at all operating temperatures. The power density of the fuel cell was ≈240 and ≈875 mW/cm2 at 600 and 800°C, respectively.

Thin films of BaCe0.8Y0.2O3-δ (BCY) were prepared by colloidal spray deposition. Dense, crack-free BCY films having a grain size of 2–7 μm were successfully deposited on NiO/BCY substrates. Electrochemical hydrogen pumping with the BCY films showed that the maximum current density increased with temperature. The maximum current density was sensitive to the moisture in the cathode gas; the value obtained with a dry cathode gas was only half that with a wet cathode gas. A very high hydrogen-pumping current density of 3.4 A/cm2 was measured at 700°C with an applied voltage of 1.5 V.

Dense ceramics with composition Ba(Ce0.7Zr0.2Yb0.1)O3-β (BCZY) were synthesized by solid state reactions, and their structures were characterized by Rietveld refinements of time-of-flight (TOF) neutron diffraction data collected for the samples at high-temperature and controlled atmospheres. The structure phase transition from orthorhombic Imma to cubic Pm3m was observed at the temperature between 500 and 700°C and in flowing 100ppm H2/Ar gases. At 900°C, the sample was subsequently exposed to different oxygen partial pressures (pO2, ranging from ∼10−17 to ∼10−23 atm) and water vapor pressures (pH2O) up to ∼0.18 atm. The expansion of lattice parameters of BCZY, instead of following the normally expected relationship with pO2, was actually correlated with the increase of pH2O, implying proton incorporation into the structures. The presence of H-containing species in the structure was confirmed by comparing both inelastic neutron scattering spectra and neutron diffraction data collected for dry and “wet” samples at 10K. The observed vibrational peaks at 104 and 150 meV and absence of a peak around 420 meV indicate the hydrogen occupation in the structure but the absence of any hydroxyl groups (hydrogen covalently bonded to oxygen). Electrical conductivities of BCZY were investigated at different temperatures in both dry and wet conditions.

Research on hydrogen separation membranes is motivated by the increasing demand for an environmentally benign, inexpensive technology for separating hydrogen from gas mixtures. Although most studies of hydrogen separation membranes have focused on proton-conducting oxides by themselves, the addition of metal to these oxides increases their hydrogen permeability and improves their mechanical stability. This study began by determining the electrical and hydrogen permeation properties of SrCe0.8Yb0.2O3−δ (SCYb). The results showed that the hydrogen permeation rate is limited by electron flow at the investigated temperatures (600 – 900°C). To further enhance hydrogen permeability, a cermet (i.e., ceramic-metal composite) membrane was made by adding Ni to the SCYb. The cermet showed no phase change after sintering in a reducing atmosphere. At 900°C, with 20% H2 /balance He as a feed gas (pH2O = 0.03 atm), the hydrogen permeation rate was 0.113 cm3/min-cm2 for Ni/SCYb (0.43-mm thick) and 0.008 cm3/min-cm2 for SCYb (0.7-mm thick). The dependences of hydrogen permeability on temperature, thickness, and hydrogen partial pressure gradients are also determined. The results demonstrate that adding Ni to SCYb considerably increases its hydrogen permeability by increasing its electron conductivity.

The inclined-substrate deposition (ISD) method for growth of biaxially textured MgO is of interest due to its applications in coated conductors based on high-temperature superconductor (HTS). The ISD method is especially attractive since it offers the potential to produce a high–quality biaxially textured layer in a simple and efficient process. In this work, Yba2Cu3O7-x (YBCO) coated conductors based on two-step deposited MgO buffer layers (ISD and homoepitaxial) on Hastelloy tapes were examined by high-resolution electron microscopy (HREM) to study both the structure of individual layers and, especially, the interfaces between them. Special attention was paid to the MgO buffer layer because of its importance to biaxial YBCO formation. TEM investigation shows the MgO [111] direction is not parallel to the substrate normal but tilted slightly toward the deposition direction. The second layer of MgO has a good epitaxial relationship with the first layer, while dislocations were found near the interface area of the MgO layers. Twin boundaries, which are in the (111) plane, were found between the ISD MgO columns. The multi-buffer layers gave better growth of epitaxial YBCO.

Inclined substrate deposition (ISD) offers the potential for rapid production of high-quality biaxially textured buffer layers suitable for YBCO-coated conductors. We have grown biaxially textured MgO films by ISD at deposition rates of 20–100 Å/sec. Columnar grain structures with a roof-tile-shaped surface were observed in the ISD-MgO films. X-ray pole figure analysis revealed that the (002) planes of the ISD-MgO films are titled at an angle from the substrate normal. A small phi-scan full-width at half maximum (FWHM) of ≈9° was observed on MgO films deposited at an inclination angle of 55°. YBCO films were also grown on ISD-MgO-buffered Hastelloy C276 substrates by pulsed laser deposition. We obtained a critical current density of ≈2 × 105 A/cm2 at 77 K in self-field on 0.5-μm-thick, 0.5-cm-wide, 1-cm-long samples. This work has demonstrated that biaxially textured ISD MgO buffer layers deposited on metal substrates are promising candidates for fabrication of high-quality YBCO-coated conductors.

Oxide high-Tc superconducting wires and tapes with high critical current density (Jc) are essential to future electrical power applications. Recently, YBa2Cu3O7−x (YBCO) thin films grown on Ni-based alloy tapes have attracted intense interest because of their promise for these applications. To achieve high Jc, buffer layers are necessary for fabricating biaxially aligned YBCO thin films. In our studies, yttria-stabilized zirconia (YSZ) layers were deposited on Ni- based alloy substrates by ion-beam assisted deposition, and CeO2 buffer layers were subsequently deposited on the YSZ layer by pulsed laser deposition (PLD) or electron beam evaporation. In addition, MgO layers were deposited on Ni-based alloy substrates by inclined substrate deposition. Finally, biaxially textured YBCO thin films were deposited on these buffered metallic substrates by PLD under optimized conditions. The orientation and in-plane textures of YBCO and the buffer layers were characterized by X-ray diffraction Ø/2Øscans, ø- scans, and pole figure analysis. The superconductive transition features were examined by measuring inductive Tc and transport Jc.

YBa2Cu3Ox (YBCO) thin films were fabricated by the trifluoroacetate (TFA) process on LaAlO3 (LAO) single crystal in an argon atmosphere. We focused on lowering the heat treatment temperature by decreasing the oxygen partial pressure to adopt the TFA process to metallic substrates. YBCO phase formation was checked by measuring Tc with the inductive method. In-plane and out-of-plane film textures were evaluated by phi-scan and omega scan, respectively. Raman spectroscopy was used to estimate grain connectivity, in-plane texture, and second-phase formation of the films. Although Raman spectroscopy revealed some evidence of cation disorder, the film prepared at 750°C shows a sharp superconducting transition at 91 K and critical current density of 1.3 MA/cm2 at 77 K. Optimal heat treatment temperature was 750°C in the argon atmosphere, which is consistent with the thermodynamic estimate that heat treatment temperature decreases as oxygen partial pressure decreases.

The mixed-conducting Sr-Fe-Co oxide has potential use as a gas separation membrane. Its superior oxygen transport reveals the feasibility of using oxide membranes in large-scale oxygen separation. Sr2Fe3-xCoxOy (with x = 0.0, 0.3, 0.6, and 1.0) samples were made by solid state reaction. To understand the oxygen transport mechanism in this system, conductivity and thermogravimetry experiments were conducted at high temperature in various oxygen partial pressure environments. The oxygen diffusion coefficient was determined from the time relaxation transient behavior of the specimen after switching the surrounding atmosphere. Mobility of the charge carrier was derived from relative conductivity and weight changes. X-ray diffraction experiments were carried out on these samples to determine their crystal structures.

Mixed-conducting oxides are used in many applications, including fuel cells, gas separation membranes, sesors, and electrocatalysis. This paper describes mixed-conducting ceramic membranes that are being developed to selectively remove oxygen and hydrogen from gas streams in a nongalvanic mode of operation (i.e., with no electrodes or external power supply). Because of its high combined electronic/ionic conductivity and significant oxygen permeability, the mixed-coducting Sr-Fe-Co oxide (SFC) has been developed for high-purity oxygen separation and/or partial oxidation of methane to synthesis gas, i.e., syngas, a mixture of carbon monoxide and hydorgen. The electronic and ionic conductivities of SFC were found to be comparable in magnitude are presented as a function of temperature. The oxygen flux through dense SFC tubes during separation of oxygen from air is compared with the oxygen flux during methane conversion.

Unlike SFC, in which the ionic and electronic conductivities are nearly equivalent, BaCe0.80Y0.20O3 (BCY) exhibits protonic conductivity that is significantly higher that its electronic coductivity. To enhance the electronic conductivity and increase hydrogen permeation, metal powder was combined with the BCY to form a cermet membrane. Nongalvanic permeation of hydrogen through the cermet memebrane was demonstrated and characterized as a function of membrane thickness. A sintering aid was developed to avoid interconnected porosity in and improve the mechanical properties of the cermet membrane.

The ac magnetic losses at power frequencies (60 Hz) were investigated for mono- and multifilament Ag-sheathed (Bi, Pb)2Sr2Ca2Cu3Oy (BSCCO-2223) tapes with similar Ic values at 77 K. The multifilament sample exhibited higher losses than the monofilament under the same conditions. Loss peaks are discussed in terms of intergranular, intragranular, and eddy current losses. Because of BSCCO's anisotropy, field orientation has a large effect on the magnitude of these peaks, even at relatively small angles. Losses for fields applied parallel to the c-axis of the textured BSCCO grains are larger by over an order of magnitude than those applied perpendicular.

The subsolidus phase relationships of the high-Tc 2223 superconductor in the (Bi, Pb)–Sr–Ca–Cu–O (BSCCO) system have been examined at 810–820 °C. All experiments were carried out at ambient pressure in a 7.5% O2 (92.5% Ar) atmosphere. Eleven phases were found to exist in equilibrium with the 2223 phase. These 11 phases include CuO and 10 oxide solid solutions. From among these phases, a total of 48 five-phase combinations including the 2223 and 2212 phases were investigated experimentally, and 16 equilibrium assemblages were found which define a multicomponent compositional space corresponding to the 2223 + 2212 solid-state compatibility region. The subsolidus data form a partial basis for future investigation of the Pb-2223 primary phase field.