B. Ma

Inclined-substrate deposition of biaxially textured magnesium oxide thin films for YBCO coated conductors

Highly textured MgO films were grown by the inclined-substrate deposition (ISD) technique at a high deposition rate. A columnar grain with a roofing-tile-shaped surface was observed in these MgO films. X-ray pole figure, and /and x-scan were used to characterize in-plane and out-of-plane textures. MgO films deposited when the incline angle a was 55 and 30 exhibited the best in-plane and out-of-plane texture, respectively. High-quality YBCO films were epitaxially grown on ISD-MgO-buffered Hastelloy C substrates by pulsed laser deposition. Tc ¼ 88 K, with sharp transition, and jc values of � 2 � 10 5 A/cm 2 at 77 K in zero field were observed on films 5 mm wide and 1 cm long. This work has demonstrated that biaxially textured ISD MgO buffer layers deposited on metal substrates are excellent candidates for fabrication of high-quality YBCO coated conductors. 2002 Elsevier Science B.V. All rights reserved.

Stability of the cubic perovskite SrFe0.8Co0.2O3−δ

Abstract Dense ceramic bars of the perovskite material SrFe 0.8 Co 0.2 O 3− δ have been synthesized by solid-state reaction and studied by in-situ neutron diffraction through the range of oxygen partial pressure ( p O 2 ) from 10 −0.68 to 10 −13.3 atm at 900 °C. Over the complete range, the material retains the cubic perovskite structure and is stable even when δ >0.5. Between air and log p O 2 =−2.3, δ increases from 0.35 to 0.44 and the lattice expands. Lowering the p O 2 further leads to an oxygen content “plateau” at δ ≈0.5, through a log p O 2 range of −3.5 to −8.6. Below this, the lattice undergoes further expansion, as oxygen is lost, most likely when Co 3+ undergoes reduction to Co 2+ . Rietveld analysis indicates that there is no deviation from the Fe/Co 80:20 ratio over the entire p O 2 range. The behavior of this perovskite is compared to that of the perovskite phase of similar composition found in a SrFeCo 0.5 O y ceramic membrane material studied under similar conditions.

Development of coated conductors by inclined substrate deposition

Abstract Inclined substrate deposition (ISD) offers the potential for rapid production of high-quality biaxially textured buffer layers suitable for YBa 2 Cu 3 O 7− δ (YBCO)-coated conductors. We have grown biaxially textured magnesium oxide (MgO) films on Hastelloy C276 (HC) substrates by ISD at deposition rates of 20–100 A/s. Scanning electron microscopy of the ISD MgO films showed columnar grain structures with a roof-tile-shaped surface. X-ray pole figure analysis revealed that the c -axis of the ISD MgO films is titled at an angle ≈32° from the substrate normal. A small full-width at half maximum of ≈9° was observed for the φ -scan of MgO films. YBCO films were grown on ISD MgO buffered HC substrates by pulsed laser deposition and were determined to be biaxially aligned with the c -axis parallel to the substrate normal. The orientation relationship between the ISD template and the top YBCO film was investigated by X-ray pole figure analysis and transmission electron microscopy. A transport critical current density of J c =5.5×10 5 A/cm 2 at 77 K in self-field was measured on a YBCO film that was 0.46-μm thick, 4-mm wide, 10-mm long.

Phase stability of SrFeCo0.5Oy under synthesis and annealing conditions

Dense ceramic tubes of the multi phase mixed ionic/electronic conductor SrFeCo0.5Oy (SFC2) have been .synthesized by solidstate reaction. Stability of the component phases of SFC2 was studied by insitu neutron diffraction in the temperature range of 900– 1200 � C in air and Ar environments. In air between 900 and 1050 � C, the material is stable, with Sr2(Fe,Co)3Oy (236) being the major phase. Above 1050 � C, 236 undergoes decomposition into perovskite and rocksalt phases, and at 1200 � C, only a small fraction of the 236 phase is stable. In Ar, the 236 phase is completely stable at 900 � C but is completely decomposed by 1100 � C, whereupon only the perovskite and rocksalt phases remain. Rietveld analysis indicates that the 236 and perovskite phases become more Fe-rich as decomposition occurs, while the perovskite phase lattice parameter and oxygen content vary readily as temperature and gas environment are changed. # 2002 Published by Elsevier Science Ltd.

Pulsed laser deposition of YBCO films on ISD MgO buffered metal tapes

Biaxially textured magnesium oxide (MgO) films deposited by inclined-substrate deposition (ISD) are desirable for rapid production of high-quality template layers for YBCO-coated conductors. High-quality YBCO films were grown on ISD MgO buffered metallic substrates by pulsed laser deposition (PLD). Columnar grains with a roof-tile surface structure were observed in the ISD MgO films. X-ray pole figure analysis revealed that the (002) planes of the ISD MgO films are tilted at an angle from the substrate normal. A small full-width at half maximum (FWHM) of ≈9° was observed in the -scan for ISD MgO films deposited at an inclination angle of 55°. In-plane texture in the ISD MgO films developed in the first ≈0.5 μm from the substrate surface, and then stabilized with further increases in film thickness. Yttria-stabilized zirconia and ceria buffer layers were deposited on the ISD MgO grown on metallic substrates prior to the deposition of YBCO by PLD. YBCO films with the c-axis parallel to the substrate normal have a unique orientation relationship with the ISD MgO films. An orientation relationship of YBCO100∥MgO111 and YBCO010∥MgO110 was measured by x-ray pole figure analyses and confirmed by transmission electron microscopy. A Tc of 91 K with a sharp transition and transport Jc of 5.5 × 105 A cm−2 at 77 K in self-field were measured on a YBCO film that was 0.46 μm thick, 4 mm wide and 10 mm long.

Study of the mixed conducting SrFeCo0.5Oy ceramic membrane material by in-situ neutron powder diffraction

Abstract Dense ceramic tubes of the multi-phase mixed ionic/electronic conductor SrFeCo0.5Oy have been synthesized by solid-state reaction, and the stability of its component phases studied using in-situ neutron diffraction over the oxygen partial pressure (pO2) range 10−0.68 to 10−15.0atm at 900°C. This being the likely conditions to which membranes are exposed in operational methane conversion reactors. This material is stable between air and log pO2 = −2.3, with Sr2(Fe,Co)3Oy (236) being the majority phase. When the oxygen partial pressure is lowered, 236 starts decomposing into perovskite and rocksalt phases. The small fraction of remaining 236 rapidly undergoes decomposition at log pO2 = −12.2, leaving only SrFeO2.5 and CoO. Rietveld analysis indicates that the oxygen content of the perovskite phase does not drop below O = 2.5 when log pO2 = −15.0, while there is an indication that CoO is reduced to cobalt metal. This decomposition at low partial pressures may be reversed when the gas is switched back to air, i.e., SrFeO2.5 + CoO re-form Sr2(Fe,Co)3Oy, to an extent that is seemingly dependent on sample and thermal history.

Growth and properties of YBCO-coated conductors on biaxially textured MgO films prepared by inclined substrate deposition

YBa2Cu3O7?? (YBCO) films were fabricated on SrRuO3 (SRO)-buffered MgO templates grown on Hastelloy C276 metallic substrates, on which the MgO layers had been deposited by inclined substrate deposition (ISD) using electron beam evaporation. YBCO and SRO films were deposited by pulsed laser deposition (PLD). ISD-MgO substrates fabricated with two different substrate inclination angles (? = 35? and 55?) were used to grow YBCO films. High transport critical current density, Jc = 1.4 ? 106?A?cm?2, has been measured at 77?K in self-field for YBCO film grown on ISD-MgO with ? = 35?, whereas YBCO film grown on ISD-MgO with ? = 55? had a lower Jc = 0.5 ? 106?A?cm?2. X-ray pole figure patterns revealed a cube-on-cube orientation relationship among YBCO, SRO, and ISD-MgO films, with the c-axis of the YBCO film being tilted. X-ray ? and -scans revealed good in-plane and out-of-plane textures of YBCO film grown on ISD-MgO substrate. The YBCO film grown on ISD-MgO with substrate inclination angle ? = 35? had a YBCO(005) -scan full width at half maximum (FWHM) = 5.8? and a YBCO(007) ?-scan FWHM = 2.8?, while YBCO film with ? = 55? had YBCO(005) -scan FWHM = 5.4? and YBCO(007) ?-scan FWHM = 2.6?.

Pulsed laser deposition of YBCO thin films on IBAD–YSZ substrates

High-quality YBa2Cu3O7−x (YBCO) films were fabricated on yttria-stabilized zirconia (YSZ)-buffered Hastelloy C276 substrates by pulsed laser deposition. YSZ was grown by ion-beam-assisted deposition. A thin (≈10 nm) CeO2 layer was deposited before the deposition of YBCO. The crystalline structure and biaxial texture of the YBCO film and the buffer layer were examined by x-ray diffraction 2θ-scan, -scan and pole-figure analysis. Epitaxial growth of the YBCO film on the buffer layer was observed. Full width at half maximum (FWHM) value of 7.4° was measured from the -scan of YBCO(103). Raman spectroscopy showed compositional uniformity and phase integrity in the YBCO films. Surface morphologies of the YBCO films were examined by scanning electron microscopy. Comparative studies indicated that the CeO2 buffer layer significantly improves the structural alignment and superconducting properties of YBCO films. Tc = 90 K, with sharp transition, and transport Jc = 2.2 × 106 A cm−2 at 77 K in zero-external field were obtained on the 0.5 μm thick YBCO films. The dependence of Jc on the FWHM of the YBCO(103) -scan indicated that high Jc is associated with low FWHM.

YBCO-coated conductors fabricated by inclined substrate deposition technique

Inclined substrate deposition (ISD) is an attractive technique for rapid production of high-quality template layers for YBCO-coated conductors. We have grown biaxially textured magnesium oxide (MgO) films on metallic substrates by ISD at rapid deposition rates, 20–100 A s−1. Scanning electron microscopy of the ISD MgO films showed columnar grain structures with a roof-tile-shaped surface. X-ray diffraction pole figure analysis revealed that the ISD MgO film is biaxially aligned with the c-axis tilted from its substrate normal. Tilt angles of and were measured on ISD MgO films deposited at 55° and 35° inclination angles, respectively. A full width at half maximum (FWHM) of was observed in the -scan for short-length ISD MgO films. A 1 m long tape of ISD MgO grown on a metallic substrate was fabricated by a reel-to-reel method. This tape has an average -scan FWHM of 16.1° with a standard deviation of 2.6°. YBCO films were grown on strontium ruthenium oxide (SRO)-buffered ISD MgO substrates by pulsed laser deposition. A superconducting critical transition temperature Tc = 91 K and critical current density Jc = 1.1 × 106 A cm−2 were measured at 77 K in self-field for a sample that is 0.3 µm thick, 2.9 mm wide, and 1.0 cm long.

Growth and properties of YBCO thin films on polycrystalline Ag substrates by inclined substrate pulsed laser deposition

Fully c-axis-oriented YBCO films were directly deposited on polycrystalline silver substrates by inclined substrate pulsed laser ablation. The orientation and microstructure of the YBCO films were characterized by x-ray diffraction 2?-scans, ?-scans and pole figure analysis. Surface morphology was examined by scanning electron microscopy. Irregular-mosaic-shaped supergrains were observed in the films. Raman spectroscopy was used to evaluate the quality of the YBCO films. The superconducting transition temperature (Tc) and the critical current density (Jc) of the films were determined by inductive and transport measurements, respectively. Tc = 91 K with sharp transition and Jc = 2.7 ? 105 A cm?2 at 77 K in zero field were obtained on a film that was 0.14 ?m thick, 5 mm wide and 10 mm long. This work demonstrated a promising approach to obtain high-Jc YBCO films on nontextured polycrystalline silver substrate.