E. A. Giess

Superconducting oxide films with high transition temperature prepared from metal trifluoroacetate precursors

Superconducting thin films of Y‐Ba‐Cu oxide have been prepared on yttria‐stabilized zirconia substrates using metal trifluoroacetate spin‐on precursors. The films exhibit an extremely sharp resistive transition with zero resistance at temperatures as high as 94 K. The superconducting phase is formed by a three‐step process: (a) decomposition of the spun‐on trifluoroacetate film to the fluorides, (b) conversion of the fluorides to oxides by reacting with water vapor, and (c) annealing followed by slow cooling in oxygen. The properties of the films depend on the amount of conversion of the fluorides by reaction with water. Films which show the presence of some unreacted barium fluoride have strong c‐axis normal preferred orientation, with a sharp resistive transition. When all the barium fluoride is converted, the film is more randomly oriented and exhibits a broader transition to zero resistance.

Epitaxial films of YBa2Cu3O7−δ on NdGaO3, LaGaO3, and SrTiO3 substrates deposited by laser ablation

Frequency‐doubled Nd:YAG laser (532 nm) pulses of 1.7 J/cm2 and 10 ns duration were used to deposit thin films of YBa2 Cu3 O7−δ by laser ablation on NdGaO3 , LaGaO3, and SrTiO3 substrates held at 725±5 °C in 0.2 Torr of O2 ambient. Electrical resistivities versus temperature of all films show normal metallic behavior and sharp superconducting transitions with Tc (R=0) at 92–93 K. Critical current densities in 0.3–0.6 μm thick, 200 μm long, and 10–30 μm wide strips were measured to be 106 A/cm2 at 60, 77, and 80 K in the films on LaGaO3, NdGaO3, and SrTiO3, respectively. X‐ray diffraction patterns show that all films grew epitaxially, with domains of only two crystalline orientations rotated 90° with respect to each other in the a‐b plane (consistent with twins), and the c axis perpendicular to the substrates. The closely matched lattice constants of the film and substrates (0.8–2.1%) result in epitaxial growth of the films.Frequency-doubled Nd:YAG laser (532 nm) pulses of 1.7 J/cm/sup 2/ and 10 ns duration were used to deposit thin films of YBa/sub 2/ Cu/sub 3/ O/sub 7-//sub delta/ by laser ablation on NdGaO/sub 3/ , LaGaO/sub 3/, and SrTiO/sub 3/ substrates held at 725 +- 5 /sup 0/C in 0.2 Torr of O/sub 2/ ambient. Electrical resistivities versus temperature of all films show normal metallic behavior and sharp superconducting transitions with T/sub c/ (R = 0) at 92--93 K. Critical current densities in 0.3--0.6 ..mu..m thick, 200 ..mu..m long, and 10--30 ..mu..m wide strips were measured to be 10/sup 6/ A/cm/sup 2/ at 60, 77, and 80 K in the films on LaGaO/sub 3/, NdGaO/sub 3/, and SrTiO/sub 3/, respectively. X-ray diffraction patterns show that all films grew epitaxially, with domains of only two crystalline orientations rotated 90/sup 0/ with respect to each other in the a-b plane (consistent with twins), and the c axis perpendicular to the substrates. The closely matched lattice constants of the film and substrates (0.8--2.1%) result in epitaxial growth of the films.

Epitaxial films of YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ on NdGaO/sub 3/, LaGaO/sub 3/, and SrTiO/sub 3/ substrates deposited by laser ablation

Frequency‐doubled Nd:YAG laser (532 nm) pulses of 1.7 J/cm2 and 10 ns duration were used to deposit thin films of YBa2 Cu3 O7−δ by laser ablation on NdGaO3 , LaGaO3, and SrTiO3 substrates held at 725±5 °C in 0.2 Torr of O2 ambient. Electrical resistivities versus temperature of all films show normal metallic behavior and sharp superconducting transitions with Tc (R=0) at 92–93 K. Critical current densities in 0.3–0.6 μm thick, 200 μm long, and 10–30 μm wide strips were measured to be 106 A/cm2 at 60, 77, and 80 K in the films on LaGaO3, NdGaO3, and SrTiO3, respectively. X‐ray diffraction patterns show that all films grew epitaxially, with domains of only two crystalline orientations rotated 90° with respect to each other in the a‐b plane (consistent with twins), and the c axis perpendicular to the substrates. The closely matched lattice constants of the film and substrates (0.8–2.1%) result in epitaxial growth of the films.Frequency-doubled Nd:YAG laser (532 nm) pulses of 1.7 J/cm/sup 2/ and 10 ns duration were used to deposit thin films of YBa/sub 2/ Cu/sub 3/ O/sub 7-//sub delta/ by laser ablation on NdGaO/sub 3/ , LaGaO/sub 3/, and SrTiO/sub 3/ substrates held at 725 +- 5 /sup 0/C in 0.2 Torr of O/sub 2/ ambient. Electrical resistivities versus temperature of all films show normal metallic behavior and sharp superconducting transitions with T/sub c/ (R = 0) at 92--93 K. Critical current densities in 0.3--0.6 ..mu..m thick, 200 ..mu..m long, and 10--30 ..mu..m wide strips were measured to be 10/sup 6/ A/cm/sup 2/ at 60, 77, and 80 K in the films on LaGaO/sub 3/, NdGaO/sub 3/, and SrTiO/sub 3/, respectively. X-ray diffraction patterns show that all films grew epitaxially, with domains of only two crystalline orientations rotated 90/sup 0/ with respect to each other in the a-b plane (consistent with twins), and the c axis perpendicular to the substrates. The closely matched lattice constants of the film and substrates (0.8--2.1%) result in epitaxial growth of the films.

Lanthanum gallate substrates for epitaxial high‐temperature superconducting thin films

We demonstrate that lanthanum gallate (LaGaO3) has considerable potential as an electronic substrate material for high‐temperature superconducting films. It provides a good lattice and thermal expansion match to YBa2Cu3O7−x, can be grown in large crystal sizes, is compatible with high‐temperature film processing, and has a reasonably low dielectric constant (e≂25) and low dielectric losses. Epitaxial YBa2Cu3O7−x films grown on LaGaO3 single‐crystal substrates by three techniques have zero resistance between 87 and 91 K.

The tungsten bronze field in the system K2O|Li2O|Nb2O5

A limited portion of the liquidus field and the entire subsolidus stability region has been determined for tungsten bronze-type solid solutions in the K2O|Li2O|Nb2O5 system. The tungsten bronze phase does not occur with completely filled alkali cation sites at the composition K3Li2Nb5O15, but exists exclusively in the high niobia region above the KNbO3|LiNbO3 pseudojoin. Equilibrium relationships defining conditions for the growth of electrooptic crystals, and dielectric, optical, and x-ray measurements establishing the influence of composition on structure and properties are presented and discussed.

Y1Ba2Cu3O7−δ thin films grown by a simple spray deposition technique

The preparation of high Tc superconducting thin films of Y1Ba2Cu3O7−δ on (100) single crystals of MgO, ZrO2 with 9% Y2O3 (yttria stabilized zirconia, or YSZ), and SrTiO3 using a simple spray deposition technique is described. Typical film growth procedure involves (a) the spraying of a stoichiometric solution of the nitrate precursors on the heated substrate (180 °C), (b) prebaking in air of the sprayed film (20 min at 500 °C), and (c) oven annealing of the film under flowing O2 (900–950 °C followed by slow cooling to 200 °C in about 3 h). X‐ray diffraction analysis of the films after each of the growing steps mentioned above shows primarily the presence of crystalline phases of the nitrates, the oxides, and the orthorhombic superconducting phase, respectively. Resistivity versus temperature measurements show that the onset and completion of the superconductive transition occur at 92 and 87 K, respectively, in films on YSZ substrate; at 95 and 80 K, respectively, in films on SrTiO3 substrate; and at 82 an...The preparation of high T/sub c/ superconducting thin films of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-//sub delta/ on (100) single crystals of MgO, ZrO/sub 2/ with 9% Y/sub 2/O/sub 3/ (yttria stabilized zirconia, or YSZ), and SrTiO/sub 3/ using a simple spray deposition technique is described. Typical film growth procedure involves (a) the spraying of a stoichiometric solution of the nitrate precursors on the heated substrate (180 /sup 0/C), (b) prebaking in air of the sprayed film (20 min at 500 /sup 0/C), and (c) oven annealing of the film under flowing O/sub 2/ (900--950 /sup 0/C followed by slow cooling to 200 /sup 0/C in about 3 h). X-ray diffraction analysis of the films after each of the growing steps mentioned above shows primarily the presence of crystalline phases of the nitrates, the oxides, and the orthorhombic superconducting phase, respectively. Resistivity versus temperature measurements show that the onset and completion of the superconductive transition occur at 92 and 87 K, respectively, in films on YSZ substrate; at 95 and 80 K, respectively, in films on SrTiO/sub 3/ substrate; and at 82 and 77 K, respectively, in films on MgO substrate.

Liquid phase epitaxial growth kinetics of magnetic garnet films grown by isothermal dipping with axial rotation

Abstract Epitaxial magnetic films of Eu 1.1 Yb 1.9 Fe 5 O 12 have been grown under controlled isothermal conditions on (111) Gd 3 Ga 5 O 12 substrates with and without rotation. The growth kinetics are adequately described by an analytical model involving diffusion (D≅3·10 −5 cm 2 /sec) through a stagnant boundary layer ( δ ≅ 100 μ m) and subsequent integration into the film according to a first order reaction (k ≅ 3·10 −3 cm/sec). These magnetic films support bubbles with a sub-micron diameter under proper bias field conditions.

Phase equilibria in the NaNbO3BaNb2O6 system

Abstract Complete liquidus and solidus equilibria have been established by DTA and quench techniques in the system NaNbO 3 BaNb 2 O 6 , which contains the pseudo-tetragonal bronze NaBa 2 Nb 5 O 15 . While little solid solution occurs in the end member compounds, the tungsten bronze phase shows extensive solid solubility from 62 to 83 mole % BaNb 2 O 6 . These results and subsolidus DTA and dielectric measurements are discussed in relation to the crystal chemistry of the bronze structure. The essential features of the phase diagram have been confirmed by Czochralski crystal growth experiments at selected melt compositions in the bronze(ss) field.

FERROELECTRIC AND OPTICAL PROPERTIES OF KSr2Nb5O15

A new transparent tetragonal crystal, KSr2Nb5O15, of the tungsten bronze type has been found to be ferroelectric with a Curie temperature of ≈160°C. At room temperature the electro‐optic coefficient, r∥, is 1.3 × 10−8 cm/V and e∥ is approximately 1,000.

The crystallization mechanism of high-cordierite glass

The crystallization mechanism of high-cordierite (2MgO·2Al2O3·5SiO2) from a bulkglass containing B2O3 and P2O5 as nucleating agents was studied using X-ray diffraction, differential thermal analysis and a polarizing microscope. Thin glass specimens, with a mirror surface, were heated rapidly in an electric furnace in the temperature range 888 to 1363° C for a desired time and then rapidly quenched to room temperature. The normal rate of growth of precipitated cordierite crystals was measured and their morphological change was observed photographically. The growth rate increased with temperature, and the maximum rate occurred at about 1250° C. The crystal morphology was hexagonalprismatic, elongated along thec-axis. Faceted interface morphology was observed when the range of undercooling was from 7 to 174° C. Judging from the relationship between the reduced growth rate and the degree of undercooling, the crystallization mechanism in the range of lower undercooling was governed by a layer growth depending on the surface nucleation mechanism. In the range of higher undercooling, continuous growth was seen and at intermediate undercooling a transition range from a layer growth to a continuous growth was evident.