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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Dependence of the critical temperature of laser-ablated YBa2Cu3O(7-delta) thin films on LaAlO3 substrate growth technique

Samples of LaAlO3 made by flame fusion and Czochralski method were subjected to the same temperature conditions that they have to undergo during the laser ablation deposition of YBa2Cu3O(7 - delta) thin films. After oxygen annealing at 750 C, the LaAlO3 substrate made by two methods experienced surface roughening. The degree of roughening on the substrate made by Czochralski method was three times greater than that on the substrate made by flame fusion. This excessive surface roughening may be the origin of the experimentally observed lowering of the critical temperature of a film deposited by laser ablation on a LaAlO3 substrate made by Czochralski method with respect to its counterpart deposited on LaAlO3 substrates made by flame fusion.

Warner, Joseph D.↗
NASA NTRS1992

Crystalline orientations of Tl2Ba2Ca2Cu3O(x) grains on MgO, SrTiO3, and LaAlO3 substrates

Crystalline orientations of Tl2Ba2Ca2Cu3O(x) grains in magnetron sputtered films on MgO (001), SrTiO3 (001), and LaAlO3 (001) substrates were investigated by scanning electron microscopy. In contrast to the nearly single crystalline films on the lattice matched substrates SrTiO3 and LaAlO3, films on the MgO (001) substrate, being polycrystalline in nature, exhibit several preferred in-plane grain orientations. These orientations agree well with a simplified theory of near-coincidence site lattices between Tl2Ba2Ca2Cu3O(x) and MgO.

Liou, S. H.↗
NASA NTRS1992

Conductor-backed coplanar waveguide resonators of Y-Ba-Cu-O and Tl-Ba-Ca-Cu-O on LaAlO3

Conductor-backed coplanar waveguide (CBCPW) resonators operating at 10.8 GHz have been fabricated from Tl-Ba-Ca-O (TBCCO) and Y-Ba-Cu-O (YBCO) thin films on LaAlO3. The resonators consist of a coplanar waveguide (CPW) patterned on the superconducting film side of the LaAlO3 substrate with a gold ground plane coated on the opposite side. These resonators were tested in the temperature range from 14 to 106 K. At 77 K, the best of our TBCCO and YBCO resonators have an unloaded quality factor (Qo) 7 and 4 times, respectively, larger than that of a similar all-gold resonator. In this study, the Qo's of the TBCCO resonators were larger than those of their YBCO counterparts throughout the aforementioned temperature range.

Miranda, F. A.↗
NASA NTRS2002

A Comparison of MOCLD With PLD Ba(x)Sr(1-x)TiO3 Thin Films on LaAlO3 for Tunable Microwave Applications

Historically, tunable dielectric devices using thin crystalline Ba(x)Sr(1-x)TiO3 (BST) films deposited on lattice-matched substrates, such as LaAlO3, have generally been grown using pulsed laser deposition (PLD). Highly oriented BST films can be grown by PLD but large projects are hampered by constraints of deposition area, deposition time and expense. The Metal-Organic Chemical Liquid Deposition (MOCLD) process allows for larger areas, faster turnover and lower cost. Several BST films deposited on LaAlO3 by MOCLD have been tested in 16 GHz coupled microstrip phase shifters. They can be compared with many PLD BST films tested in the same circuit design. The MOCLD phase shifter performance of 293 deg. phase shift with 53 V/micron dc bias and a figure of merit of 47 deg./dB is comparable to the most highly oriented PLD BST films. The PLD BST films used here have measured XRD full-width-at-half-maxima (FWHM) as low as 0.047 deg.. The best FWHM of these MOCLD BST films has been measured to be 0.058 deg.

VanKeuls, F. W.↗
DOE OSTI2020

Materials Data on LaAlO3 by Materials Project

LaAlO3 crystallizes in the trigonal R-3c space group. The structure is three-dimensional. La3+ is bonded to twelve equivalent O2- atoms to form distorted LaO12 cuboctahedra that share corners with twelve equivalent LaO12 cuboctahedra, faces with six equivalent LaO12 cuboctahedra, and faces with eight equivalent AlO6 octahedra. There are a spread of La–O bond distances ranging from 2.49–2.92 Å. Al3+ is bonded to six equivalent O2- atoms to form AlO6 octahedra that share corners with six equivalent AlO6 octahedra and faces with eight equivalent LaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 13°. All Al–O bond lengths are 1.92 Å. O2- is bonded in a 2-coordinate geometry to four equivalent La3+ and two equivalent Al3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaAlO3 by Materials Project

LaAlO3 is (Cubic) Perovskite structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. La3+ is bonded to twelve equivalent O2- atoms to form LaO12 cuboctahedra that share corners with twelve equivalent LaO12 cuboctahedra, faces with six equivalent LaO12 cuboctahedra, and faces with eight equivalent AlO6 octahedra. All La–O bond lengths are 2.69 Å. Al3+ is bonded to six equivalent O2- atoms to form AlO6 octahedra that share corners with six equivalent AlO6 octahedra and faces with eight equivalent LaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Al–O bond lengths are 1.91 Å. O2- is bonded in a distorted linear geometry to four equivalent La3+ and two equivalent Al3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaAlO3 by Materials Project

LaAlO3 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are two inequivalent La3+ sites. In the first La3+ site, La3+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of La–O bond distances ranging from 2.33–3.05 Å. In the second La3+ site, La3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of La–O bond distances ranging from 2.28–2.63 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to five O2- atoms to form AlO5 trigonal bipyramids that share a cornercorner with one AlO6 octahedra, corners with two equivalent AlO5 trigonal bipyramids, and edges with two equivalent AlO6 octahedra. The corner-sharing octahedral tilt angles are 34°. There are a spread of Al–O bond distances ranging from 1.78–1.90 Å. In the second Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent AlO6 octahedra, a cornercorner with one AlO5 trigonal bipyramid, and edges with two equivalent AlO5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 9°. There are a spread of Al–O bond distances ranging from 1.90–2.01 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted see-saw-like geometry to three La3+ and one Al3+ atom. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to four La3+ and two Al3+ atoms. In the third O2- site, O2- is bonded in a distorted see-saw-like geometry to one La3+ and three Al3+ atoms. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to two La3+ and three Al3+ atoms. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to three La3+ and one Al3+ atom. In the sixth O2- site, O2- is bonded to three La3+ and one Al3+ atom to form distorted corner-sharing OLa3Al tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaAlO3 by Materials Project

LaAlO3 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are three inequivalent La3+ sites. In the first La3+ site, La3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of La–O bond distances ranging from 2.47–2.72 Å. In the second La3+ site, La3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of La–O bond distances ranging from 2.30–2.69 Å. In the third La3+ site, La3+ is bonded to six O2- atoms to form distorted LaO6 octahedra that share corners with six AlO4 tetrahedra and an edgeedge with one LaO6 octahedra. There are a spread of La–O bond distances ranging from 2.39–2.55 Å. There are three inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with two equivalent LaO6 octahedra and corners with two AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 63–72°. There are a spread of Al–O bond distances ranging from 1.76–1.79 Å. In the second Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share a cornercorner with one LaO6 octahedra and corners with two AlO4 tetrahedra. The corner-sharing octahedral tilt angles are 52°. There are a spread of Al–O bond distances ranging from 1.77–1.80 Å. In the third Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with three equivalent LaO6 octahedra and corners with two AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 56–72°. There are a spread of Al–O bond distances ranging from 1.76–1.80 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to three La3+ and one Al3+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to three La3+ and one Al3+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to three La3+ and one Al3+ atom. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to three La3+ and one Al3+ atom. In the fifth O2- site, O2- is bonded to three La3+ and one Al3+ atom to form a mixture of distorted edge and corner-sharing OLa3Al tetrahedra. In the sixth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one La3+ and two Al3+ atoms. In the seventh O2- site, O2- is bonded to three La3+ and one Al3+ atom to form a mixture of distorted edge and corner-sharing OLa3Al tetrahedra. In the eighth O2- site, O2- is bonded in a bent 120 degrees geometry to two Al3+ atoms. In the ninth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one La3+ and two Al3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaAlO3 by Materials Project

LaAlO3 crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. La3+ is bonded to twelve O2- atoms to form distorted LaO12 cuboctahedra that share corners with twelve equivalent LaO12 cuboctahedra, faces with six equivalent LaO12 cuboctahedra, and faces with eight equivalent AlO6 octahedra. There are a spread of La–O bond distances ranging from 2.50–2.92 Å. Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six equivalent AlO6 octahedra and faces with eight equivalent LaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 9–13°. All Al–O bond lengths are 1.92 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to four equivalent La3+ and two equivalent Al3+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to four equivalent La3+ and two equivalent Al3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaAlO3 by Materials Project

LaAlO3 crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. La3+ is bonded to twelve O2- atoms to form LaO12 cuboctahedra that share corners with twelve equivalent LaO12 cuboctahedra, faces with six equivalent LaO12 cuboctahedra, and faces with eight equivalent AlO6 octahedra. There are a spread of La–O bond distances ranging from 2.55–2.86 Å. Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six equivalent AlO6 octahedra and faces with eight equivalent LaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–13°. All Al–O bond lengths are 1.92 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to four equivalent La3+ and two equivalent Al3+ atoms. In the second O2- site, O2- is bonded in a distorted linear geometry to four equivalent La3+ and two equivalent Al3+ atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1989

Growth and patterning of laser ablated superconducting YBa2Cu3O7 films on LaAlO3 substrates

A high quality superconducting film on a substrate with a low dielectric constant is desired for passive microwave circuit applications. In addition, it is essential that the patterning process does not effect the superconducting properties of the thin films to achieve the highest circuit operating temperatures. YBa2Cu3O7 superconducting films were grown on lanthanum aluminate substrates using laser ablation with resulting maximum transition temperature (T sub c) of 90 K. The films were grown on a LaAlO3 which was at 775 C and in 170 mtorr of oxygen and slowly cooled to room temperature in 1 atm of oxygen. These films were then processed using photolithography and a negative photoresist with an etch solution of bromine and ethanol. Results are presented on the effect of the processing on T(sub c) of the film and the microwave properties of the patterned films.

Warner, J. D.↗
NASA NTRS1992

C-band superconductor/semiconductor hybrid field-effect transistor amplifier on a LaAlO3 substrate

A single-stage C-band superconductor/semiconductor hybrid field-effect transistor amplifier was designed, fabricated, and tested at 77 K. The large area (1 inch x 0.5 inches) high temperature superconducting Tl-Ba-Ca-Cu-O (TBCCO) thin film was rf magnetron sputtered onto a LaAlO3 substrate. The film had a transition temperature of about 92 K after it was patterned and etched. The amplifier showed a gain of 6 dB and a 3 dB bandwidth of 100 MHz centered at 7.9 GHz. An identical gold amplifier circuit was tested at 77 K, and these results are compared with those from the hybrid amplifier.

Nahra, J. J.↗
NASA NTRS1992

Conductor-backed coplanar waveguide resonators of YBa2Cu3O(7-delta) on LaAlO3

Conductor-backed coplanar waveguide (CBCPW) resonators operating at 10.8 GHz have been fabricated from laser ablated and off-axis magnetron sputtered YBa2Cu3O(7-delta) (YBCO) high-temperature superconducting (HTS) thin films on LaAlO3. These resonators were tested in the temperature range from 14 to 92 K. The unloaded quality factor at 77 K of the HTS CBCPW resonators was 3 to 4 times that of a similar gold resonator. To the authors' knowledge, these results represent the first reported measurements of HTS-based CBCPW resonators.

Miranda, Felix A.↗
NASA NTRS2003

A Comparison of MOCLD With PLD Ba(x)Sr(1-x)TiO3 Thin Films on LaAlO3 for Tunable Microwave Applications

Historically, tunable dielectric devices using thin crystalline Ba(x)Sr(1-x),TiO3 (BST) films deposited on lattice-matched substrates, such as LaAlO3 have generally been grown using pulsed laser deposition (PLD). Highly oriented BST films can be grown by PLD but large projects are hampered by constraints of deposition area, deposition time and expense. The Metal-Organic Chemical Liquid Deposition (MOCLD) process allows for larger areas, faster turnover and lower cost. Several BST films deposited on LaAlO, by MOCLD have been tested in 16 GHz coupled microstrip phase shifters. They can be compared with many PLD BST films tested in the same circuit design. The MOCLD phase shifter performance of 293 degree phase shift with 53 V/micron dc bias and a figure of merit of 47 degree/dB is comparable to the most highly oriented PLD BST films. The PLD BST films used here have measured XRD full-width-at-half-maxima (FWHM) as low as 0.047 degrees. The best FWHM of these MOCLD BST films has been measured to be 0.058 degrees.

VanKeuls, F. W.↗
NASA NTRS1993

Microwave properties and characterization of co-evaporated BSCCO thin films

An extensive characterization of Bi-Sr-Ca-Cu-O (BSCCO) thin films deposited by co-evaporation on LaAlO3 and SrTiO3 substrates was performed. The films had a T(sub c) (R = O) of approximately 78 K, and were predominantly c-axis oriented, with critical current densities (J(sub c)) at 4.5 K of 1.6 x 10(exp 6) and 1.1 x 10(exp 6) A cm(sup -2), for the samples on SrTiO3 and LaAlO3, respectively. The microwave properties of the films were examined by three techniques. The complex conductivity sigma(sub *) = sigma(sub 1) - j(sigma(sub 2)) and the magnetic penetration depth (A) were measured by power transmission at 30.6 GHz; the surface resistance (R(sub s)) was measured using a cavity resonator at 58.9 GHz, and the transmission line losses were determined by measuring the quality factor (Q) of a linear microstrip resonator at 10.4 and 20.2 GHz. The complex conductivity for the film on LaAlO3 was determined to be (2.0-j10) x 10(exp 5) S/m at 77 K. It was observed that in the superconducting state sigma(sub 1) deviates from both the Bardeen-Cooper-Schrieffer (BCS) theory and the two-fluid model. Values of lambda were found to be approximately 2.0 and 1.1 microns at 77 K and 20 K respectively, and were obtained for the film on LaAlO3. The value of lambda at 20 K was approximately three times larger than that of BSCCO single crystals. R(sub s) values of 865 and 1391 mOmega were obtained for the films on SrTiO3 and LaAlO3, respectively, at 77 K and 58.9 GHz. Unloaded Q factors at 20 K of approximately 1100 and 800 at 10.4 and 20.2 GHz respectively, were measured for the BSCCO resonator. Unloaded Q values of 290 and 405 at 20 K were obtained at 10.4 GHz and 20.2 GHz respectively, for an all gold (Au) resonator.

Miranda, F. A.↗
NASA NTRS1990

Laser ablated high T(sub c) superconducting thin YBa2Cu3O(7-x) films on substrates suitable for microwave applications

The development of high temperature superconducting YBa2Cu3O(7-x) thin films on substrates suitable for microwave applications is of great interest for evaluating their applications for space radar, communication, and sensor systems. Thin films of YBa2Cu3O(7-x) were formed on SrTiO3, ZrO2, MgO, and LaAlO3 substrates by laser ablation. The wavelength used was 248 nm from a KrF excimer laser. During deposition the films were heated to 600 C in a flowing oxygen environment, and required no post annealing. The low substrate temperature during deposition with no post annealing gave films which were smooth, which had their c-axis aligned to the substrates, and which had grains ranging from 0.2 to 0.5 microns in size. The films being c-axis aligned gave excellent surface resistance at 35 GHz which was lower than that of copper at 77 K. At present, LaAlO3 substrates with a dielectric constant of 22, appears suitable as a substrate for microwave and electronic applications. The films were characterized by resistance-temperature measurements, scanning electron microscopy, and x ray diffraction. The highest critical transition temperatures (T sub c) are above 89 K for films on SrTiO3 and LaAlO3, above 88 K for ZrO2, and above 86 K for MgO. The critical current density (J sub c) of the films on SrTiO3 is above 2 x 10(exp 6) amperes/sq cm at 77 K. The T(sub c) and J(sub c) are reported as a function of laser power, composition of the substrate, and temperature of the substrate during deposition.

Warner, J. D.↗
NASA NTRS1989

Sequentially evaporated thin Y-Ba-Co-O superconducting films on microwave substrates

The development of high T sub c superconducting thin films on various microwave substrates is of major interest in space electronic systems. Thin films of YBa2Cu3O(7-Delta) were formed on SrTiO3, MgO, ZrO2 coated Al2O3, and LaAlO3 substrates by multi-layer sequential evaporation and subsequent annealing in oxygen. The technique allows controlled deposition of Cu, BaF2 and Y layers, as well as the ZrO buffer layers, to achieve reproducibility for microwave circuit fabrication. The three layer structure of Cu/BaF2/Y is repeated a minimum of four times. The films were annealed in an ambient of oxygen bubbled through water at temperatures between 850 C and 900 C followed by slow cooling (-2 C/minute) to 450 C, a low temperature anneal, and slow cooling to room temperature. Annealing times ranged from 15 minutes to 5 hrs. at high temperature and 0 to 6 hr. at 450 C. Silver contacts for four probe electrical measurements were formed by evaporation followed with an anneal at 500 C. The films were characterized by resistance-temperature measurements, energy dispersive X-ray spectroscopy, X-ray diffraction, and scanning electron microscopy. Critical transition temperatures ranged from 30 K to 87 K as a function of the substrate, composition of the film, thicknesses of the layers, and annealing conditions. Microwave ring resonator circuits were also patterned on these MgO and LaAlO3 substrates.

Valco, G. J.↗