Rachel E. Koritala

Lead Lanthanum Zirconate Titanate Ceramic Thin Films for Energy Storage

An acetic-acid-based sol-gel method was used to deposit lead lanthanum zirconate titanate (PLZT, 8/52/48) thin films on either platinized silicon (Pt/Si) or nickel buffered by a lanthanum nickel oxide buffer layer (LNO/Ni). X-ray diffraction and scanning electron microscopy of the samples revealed that dense polycrystalline PLZT thin films formed without apparent defects or secondary phases. The dielectric breakdown strength was greater in PLZT thin films deposited on LNO/Ni compared with those on Pt/Si, leading to better energy storage. Finally, optimized dielectric properties were determined for a 3-μm-thick PLZT/LNO/Ni capacitor for energy storage purposes: DC dielectric breakdown strength of ∼1.6 MV/cm (480 V), energy density of ∼22 J/cc, energy storage efficiency of ∼77%, and permittivity of ∼1100. These values are very stable from room temperature to 150 °C, indicating that cost-effective, volumetrically efficient capacitors can be fabricated for high-power energy storage.

Temperature-dependent energy storage properties of antiferroelectric Pb0.96La0.04Zr0.98Ti0.02O3 thin films

The energy storage properties of antiferroelectric (AFE) Pb0.96La0.04Zr0.98Ti0.02O3 (PLZT 4/98/2) thin films were investigated as a function of temperature and applied electric field. The results indicated that recoverable energy density (Ure) and charge-discharge efficiency (η) of PLZT (4/98/2) depend weakly on temperature (from room temperature to 225 °C), while Ure increases linearly and η decreases exponentially with increasing electric field at room temperature. These findings are explained qualitatively on the basis of the kinetics of the temperature-induced transition of AFE-to-paraelectric phase and the field-induced transition of AFE-to-ferroelectric phase, respectively. The high Ure (≈61 J/cm3) and low leakage current density (≈3.5 × 10−8 and 3.5 × 10−5 A/cm2 at 25 and 225 °C, respectively) indicate that antiferroelectric PLZT (4/98/2) is a promising material for high-power energy storage.

Mechanism and processing dependence of biaxial texture development in magnesium oxide thin films grown by inclined-substrate deposition

Biaxially textured thin films of MgO were deposited on metal foils as epitaxial template layers for high-T/sub c/ superconducting tapes. The MgO was deposited by electron beam evaporation on substrates inclined to the atomic vapor. The processing dependence of biaxial texture on inclination angle, deposition rate, film thickness, and substrate was investigated by four-circle X ray diffraction and selected-area electron diffraction. Texturing of the MgO was a selective growth process whereby the texture improves with increasing film thickness. This growth process differs from the texturing of MgO in ion-beam-assisted deposition, which is nucleation controlled and requires an amorphous substrate. It was experimentally found that the in-plane texture of the MgO thick films was not dependent on deposition rate from 2.5 to 100 /spl Aring//s, making this technique amenable to cost-effective production. This result has important implications to manufacturing scale-up of YBa/sub 2/Cu/sub 3/O/sub x/ coated tapes. The mechanism for the creation of biaxial texture in the MgO films was determined to be from the combined effects of the cubic equilibrium crystal habit of MgO and columnar self-shadowing.

Sectioning of multilayers to make a multilayer Laue lens

We report a process to fabricate multilayer Laue lenses (MLLs) by sectioning and thinning multilayer films. This method can produce a linear zone plate structure with a very large ratio of zone depth to width (e.g., >1000), orders of magnitude larger than can be attained with photolithography. Consequently, MLLs are advantageous for efficient nanofocusing of hard x rays. MLL structures prepared by the technique reported here have been tested at an x-ray energy of 19.5 keV, and a diffraction-limited performance was observed. The present article reports the fabrication techniques that were used to make the MLLs.

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.

Compressive creep of mullite containing Y2O3

Compressive creep of mullite and mullite containing 5 and 9 wt% Y{sub 2}O{sub 3} has been investigated in the temperature range of 1300-1400 C over stresses between {approx}0.6 and 40 MPa in air. The nominally single-phase mullite deforms by diffusional flow with a stress exponent of 1 (for higher stresses) and an activation energy of 385{+-}20 kJ/mol. It is likely that the rate-controlling diffusing species is oxygen. Creep of the Y{sub 2}O{sub 3}-containing specimens was similar to that of the pure mullite at 1300 C. Near and above the temperature at which melting was observed in DTA, the Y{sub 2}O{sub 3}-containing specimens crept significantly faster than the pure mullite. Models of creep of materials that contain a glass phase can explain most, but not all, of the observed behavior. Creep rates were not significantly affected by partial crystallization of the glass to Y{sub 2}Si{sub 2}O{sub 7}, but the crystallized specimens exhibited cavitation at larger strains.

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.

Transmission electron microscopy investigation of texture development in magnesium oxide buffer layers

Biaxially textured magnesium oxide (MgO) buffer layers were grown by inclined substrate deposition and examined before YBa/sub 2/Cu/sub 3/O/sub 7-x/ deposition to optimize their texture. Transmission electron microscopy of buffer layers in both cross-sectional and plan view was used to investigate film microstructure and texture development as a function of deposition thickness (0.05-3 /spl mu/m) and substrate inclination angle (0-55/spl deg/ from the substrate normal). It was determined that the combined effects of preferential growth of the {200} equilibrium crystal habit of MgO and shadowing by columnar grains led to the development of off-axis [200]-textured films.

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.

Growth and properties of YBCO-coated conductors fabricated by inclined-substrate deposition

YBCO-coated conductors with high current-carrying capability are desirable for electric power transmission applications. Inclined-substrate deposition (ISD) is capable of producing high-quality biaxially textured template films, which are important for fabrication of YBCO-coated conductors. We have grown biaxially textured ISD-MgO template films on flexible metallic substrates at deposition rates of 2-10 nm/sec. Columnar grains with a roof-tile-shaped surface structure were observed on the ISD-MgO films. X-ray pole figure analysis revealed that the ISD-MgO film is biaxially textured and its c-axis is titled at an angle from the substrate normal. Strontium ruthenium oxide (SRO) buffer films were epitaxially grown on ISD-MgO by pulsed laser deposition prior to the deposition of YBCO. Low /spl phi/-scan full-width at half maximum (FWHM) values of 6/spl deg/ and 7/spl deg/ were observed for YBCO and SRO, respectively. T/sub c/ of 91 K with a sharp transition and transport J/sub c/ over 1.4 MA/cm/sup 2/ at 77 K in self-field were measured on YBCO coated conductors grown with ISD MgO architectures using a SRO buffer.