YSZ Films Research Articles

The Effect of Anode Thickness in SOFCs with Anode Supported YSZ Film

The Effect of Anode Thickness in SOFCs with Anode Supported YSZ Film

Development of Y-123-coated conductors by IBAD process

Scale-up of the ion-beam-assisted deposition (IBAD) method was surveyed on both YSZ buffer layer and Y-123 film depositions with a few meters sample length. Repeated depositions of YSZ films were performed with varied tape-shifting speed. Three-meter-long YSZ textured template layers were formed by IBAD on Ni–Cr alloy tapes with an in-plane mosaic spread of 17°–19° in whole length. The pulsed laser deposition (PLD) process for Y-123 formations was improved in the lifetime of Y-123 targets, and over 2-m-length samples were formed without recognizable thickness variations of Y-123. I c of 25.3 A and J c of 2.4×10 5 A/cm 2 were obtained in 2.1-m-length samples at 77 K, 0 T.

Structural characterisation of thermal barrier coatings deposited using electrostatic spray assisted vapour deposition method

Abstract Gas turbine engines provide one of the harshest environments for engineering components today. Thermal barrier coatings (TBCs) such as 8wt.% Y2O3–ZrO2 (YSZ) are able to protect the blades and can lead to further increases in operating temperature by providing an effective thermal barrier on the blades. YSZ coatings were deposited using a novel and cost-effective electrostatic spray-assisted vapour deposition (ESAVD) technique. This method involves spraying atomised precursor droplets across an electric field, where they undergo decomposition and/or chemical reactions in the vapour phase near the vicinity of the heated substrate. A solution containing zirconium and yttrium alkoxide precursors was used for the deposition of YSZ films. The coatings were characterised using a combination of scanning electron microscopy, X-ray diffraction (XRD) and Raman spectroscopy. Thick and uniform YSZ films with columnar growth features were successfully deposited using the ESAVD method. The Raman investigations showed the presence of carbon in the as-deposited coatings. However, the carbon was removed when the YSZ coating was heat-treated at 1000°C for 2 h to improve the adhesion of the TBC coating to the bond coat.

A STUDY OF NO.2 SERIES ZrO2(Y2O3) THIN FILM BY SLOW POSITRONS BEAM

The ZrO2(Y2O3) thin film materials are studed b y slow positron beam.The ZrO2(Y2O3) thin film m aterials are made by r f puttering without biasing,heat treatment of liner being at 300℃ in pure Ar atmosphere.We discovered that the defects distribute themse lves in different depths of the thin film.The tempearture influences the distril ution of defects in the YSZ thin films.And we discuss briefly the method to make dense and high-quality YSZ films.

Growth of oxide buffer layers and YBCO films on various substrates by pulsed injection CVD

Bilayers composed from a YSZ or CeO 2 buffer layer and a YBCO film were in situ grown on monocrystalline sapphire, MgO. silicon, vicinally polished sapphire and MgO substrates by single source pulsed injection CVD. Zr. Ce. Y. Ba and Cu 2,2,6,6-tetramethyl-3,5-heptandionates dissolved in organic solvent were used for film deposition. CeO 2 /YBCO bilayers on sapphire were grown epitaxially and exhibited critical current densities up to 10 6 A/cm 2 at 77 K. YSZ and CeO 2 buffer layers on MgO substrates did not improved the properties of YBCO layers compared with YBCO films deposited directly on MgO surface; however, interesting microstructural properties of these heterostructures were found. Homogeneous YSZ films were also deposited on large Si substrates (3 inches in diameter).

Processing dependence of biaxial texture in yttria-stabilized zirconia by ion-beam-assisted deposition

Biaxially textured yttria (8 mol%)-stabilized zirconia (YSZ) thin films were deposited on randomly oriented Hastelloy C and Stainless Steel 304 at room temperature as a buffer layer for subsequent deposition of oriented YBa/sub 2/Cu/sub 3/O/sub x/ films. The 0.16-1.3 /spl mu/m thick YSZ films were deposited by e-beam evaporation at rates of 1.2-3.2 /spl Aring//sec. Biaxially textured films were produced with an Ar/O/sub 2/ ion beam directed at the substrate during film growth. X-ray diffraction was used to study in-plane and out-of-plane orientation as a function of ion bombardment angle, film thickness, ion-to-atom flux ratio, and substrate material. In-plane and out-of-plane average-misorientation angles on these YSZ films that were deposited by ion-beam-assisted deposition were as low as 17 and 5.4/spl deg/, respectively, on as-received substrates.

Chemical spray deposition of YSZ and GCO solid electrolyte films

The chemical deposition of YSZ and GCO solid electrolyte films by spraying of precursor solutions onto heated substrates was investigated using ultrasonic atomisation. Various precursors (chlorides, acetylacetonates and alcoxides of the corresponding metals) and solvents (ethanol, diethylene glycol, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate and triethylene glycol monobutyl ether) were tested. The experimental results are presented and the mechanism of the film formation is discussed. It is shown that dense thin films of YSZ and GCO are formed from liquid droplets spreading on the substrate surface. A novel technology for thin film electrolyte solid oxide fuel cells which uses etched metallic meshes as an electrolyte support and current collector is demonstrated.

The process, structure and performance of pen cells for the intermediate temperature SOFCs

The paper is principally concerned with strategic investigations based on the development of planar supported thin film electrolyte (STEF) configurations for intermediate temperature SOFC applications. A novel and cost effective electrostatic assisted vapour deposition process has been used to deposit dense YSZ film onto the porous anode substrates. Several approaches were investigated to deposit a dense and crack-free YSZ film onto the porous anode substrate during the fabrication of PEN structure. The use of an amorphous YSZ thin film followed by a crystalline YSZ film deposition using the continuous EAVD process seem to be able to produce a dense and crack-free YSZ film onto the porous NiO–YSZ substrate with a well defined interface. Individual dense/porous films and PEN assembly were characterised using XRD, SEM, and I–V test techniques for structural examination and electrical measurements.

Y2O3-Stabilized ZrO2 Thin Films Prepared by Metalorganic Chemical Vapor Deposition

Zirconia films stabilized by Y2O3 were deposited by metal-organic chemical vapor techniques onto various crystalline substrates. Y2O3, ZrO2 and mixtures of these two were deposited and characterized. The deposition rate, the film composition and the structure could be systematically varied through the Y(C11H19O2)3, Zr(O·t-C4H9)4 and O2 source gas ratios and the substrate temperature. The Y/Zr ratio could be adjusted by controlling the ratio in Y(C11H19O2)3 to Zr(O·t-C4H9)4 partial pressures. However, the Y/Zr ratio was found to be smaller than that estimated based on the deposition rates of unmixed Y2O3 and ZrO2 films. The activation energy of the Y2O3 component in YSZ film growth was similar to that of the ZrO2 component in YSZ films. These YSZ values were more than 4 times larger than those of unmixed Y2O3 or ZrO2 films.

Growth mechanism of biaxially textured YSZ films deposited by ion-beam-assisted deposition

Biaxially textured YSZ films have a large technical relevance for power or electronic applications of HTS films. The YSZ serves as a diffusion barrier and as a template for an epitaxial growth of the HTS. On polycrystalline substrates the biaxial alignment is achieved by using an ion-beam-assisted deposition method. The best obtained textures were characterized by a full width at half maximum of 7° in an 〈111〉 x-ray diffraction Φ scan. The FWHM decreases with increasing film thickness. The growth mechanism is investigated with respect to three important effects: nucleation, growth selection, and homoepitaxial growth. It could be shown that during nucleation at the beginning of deposition the angle between the assisting beam and the substrate normal has to be fixed at 55°, whereas during the growth selection this angle can be varied. Especially the homoepitaxial effects allow changes in the deposition conditions without destroying the already achieved texture quality.

Growth structure of yttria-stabilized-zirconia films during off-normal ion-beam-assisted deposition

Biaxially aligned YSZ thin films with strong [100] fiber texture were formed on a polycrystalline Ni-based alloy by off-normal ion-beam-assisted deposition. Growth structures were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), etc., and the alignment mechanism was discussed using a selective growth model. Peculiar structural evolution of the crystalline orientation was observed and its development was well described by an exponential equation. It was explained as a collaboration of an anisotropic growth condition and epitaxial crystallization. The [100] fiber texture was formed by columnar structures of diameter of 30–100 nm, which were composed of 5–10 nm diameter crystallites. Very smooth surfaces were observed by AFM imaging with a roughness of 2–3 nm and a peculiar ripple structure. The origin of the azimuthal alignment was discussed with emphasis on the surface structure of YSZ films produced using ion-beam-assisted deposition (IBAD) and the etching rate measurements of (100) surfaces of YSZ single crystals.

Material Properties of Heteroepitaxial Ir and Pb(ZrxTi1-x)O3 Films on (100)(ZrO2)1-x(Y2O3)x/(100)Si Structure Prepared by Sputtering

We investigated the crystalline quality and electrical properties of heteroepitaxial Ir and Pb(ZrxTi1-x)O3 films deposited by sputtering on an epitaxial (100)(ZrO2)1-x(Y2O3)x film/(100)Si substrate structure. The Ir(100) and Ir(111) orientations were enhanced and reduced, respectively, by decreasing the deposition rate. The φ scan pattern of X-ray diffraction showed that the (100) oriented film was the heteroepitaxial film on the epitaxial (100)YSZ film with a cube on cube relationship. On this epitaxial (100)Ir film, a heteroepitaxial (001)PZT film was obtained by reactive sputtering. The P–E hysteresis loop of the 200-nm-thick epitaxial PZT film showed a well-saturated square shape at the ac amplitude of 3 V, and the remanent polarization 2Pr and the coercive field 2Ec were 83 µC/cm2 and 131 kV/cm, respectively. The leakage current was about 1×10-7 A/cm2 at ±5 V.

Electron microscopy study of interfacial structure and reaction of Yba2Cu3O7/Y-ZrO2 films on LaAlO3 substrates

The detailed structure and interfacial reaction of epitaxial Yba2Cu3O7/Y-ZrO2 (YBCO/YSZ) films grown by chemical vapor deposition (CVD) on LaAlO3 (LAO) substrates are investigated by means of high-resolution electron microscopy (HREM), analytical transmission electron microscopy, and scanning transmission electron microscopy (STEM). The epitaxial relations of YBCO/YSZ/LAO are [100]YBCO // [110]YSZ // [100]LAO and (001)YBCO // (001)YSZ // (001)LAO. The optimum atomic configuration at the YSZ/LAO interface, in which oxygen is the first atomic layer on LAO, is proposed by using HREM combined with image simulation based on the atomic structure models of the interface. Near the YBCO/YSZ interface, two localized interfacial reaction products are formed: (i) a Y-rich modulated ZrO2 structure at the surface of the YSZ film, which may be caused by the diffusion of Y into the YSZ grains; (ii) an intergranular BaZrO3 phase formed by the diffusion of Ba along the columnar grain boundaries of the YSZ film during YBCO growth.

Amperometric oxygen sensors based on dense Tb–Y–Zr–O electrodes

The fabrication and operation of a new type of amperometric linear response oxygen sensor is demonstrated that utilizes a 16 μm thick, dense Tb–YSZ film of composition Y 0.2Tb 0.24Zr 0.56O 2− y as a solid state chemical oxygen diffusion barrier. The device exhibits a near linear response between 750 and 850°C between 0.2 and 4.5% O 2 in nitrogen. The effective linear range of operation at 800°C is extended to above 8.0% O 2 with the application of albite (Na–Al–Si–O) glass to limit leakage at the edges (gas–substrate-diffusion barrier interface) of the device. Thin film high temperature cyclic voltammetry performed on Tb–YSZ films of similar stoichiometry indicate thermodynamic stability to below 10 −30 atm pO 2 at 750°C. The initial performance of this device taken together with the inherent chemical stability of the diffusion barrier suggests that devices of this type may be suitable for use as control sensors for lean-burn internal combustion engines.

High-Resolution Studies of Grain Boundary Structure in Yttria-Stabilized Cubic Zirconia Thin Films Grown by MOCVD

Polycrystalline cubic-phase YSZ films with a colummar grain morphology were sunthesized by MOCVD. Under suitable growth and annealing conditions highly (001) textured films were obtained and used for investigations of [001] tilt grain boundaries (GBs) by TEM, AEM and HREM. Individual primary GB dislocations in low-angle GBs were imaged by Fresnel contrast and HREM techniques. Both low and high-angle GBs were well structured at the atomic scale. No amorphous GB phases were found in any of the GBs. However, yttria segregation to GBs after high-temperature anneals was indicated by EDS. The atomic-scale structures, although in detail quite different from previously investigated oxide GBs, such as the Σ5, (210) GB in NiO, share a number of structural features with other oxide GBs. These include the tendency toward coherence between low-index planes crossing the GB, misfit localization, and the formation of many types of asymmetric facets that include low-index planes. The fact that well-structured GBs free of secondary phases can be produced in YSZ is of technological importance, especially for fast-ion conduction applications, such as in high temperature fuel cells.

Rapid thermal annealing of zirconia films deposited by spray pyrolysis

Zirconia (8 mol% yttria) (YSZ) amorphous layers were deposited by spray pyrolysis on Si oxidized substrates and crystallized by rapid thermal treatment in a home-made halogen lamps furnace. Uniform films were obtained by depositing up to six layers, followed by the thermal treatment. X-ray analysis showed that the cubic phase is obtained during the initial stage of the annealing process. No significant differences with increasing annealing time nor interaction between the YSZ film and the substrate were observed. Ionic conduction in air, with activation energies comparable to those of bulk YSZ ceramics, was observed. The electrical characteristics of the films make them suitable for microelectronics applications.

Preparation of YSZ Thin Film on Porous Electrode of SOFC

AbstractPorous electrode substrate of La0.7Sr0.2MnO3 was used as the support for the deposition of YSZ thin films. The porosity of the electrode substrate was controlled by sintering temperature and particle size of powders. Thin films of YSZ were fabricated on the electrode by sol-gel method. The YSZ film fabricated by 10-fold coating with 0.05M YSZ sol containing TEA was continuous and crack-free one of 5 mm in thickness. However, hydrogen permeation measurement showed that there was a very small leakage of hydrogen in the fabricated film. In addition to sol-gel method, another technique such as EVD should be employed to make the film completely gas-tight.

Room-temperature deposition of yttria-stabilized zirconia buffer layer on metallic substrates by laser ablation

We investigated the deposition of YSZ buffer layers on polycrystalline metallic substrate at low temperature and low oxygen pressure. The (100) preferred orientation can be obtained in the YSZ films and was explained by the model of growth-based orientation selection. Optimizations of oxygen partial pressure and target distance were done to offer referable values for IBAD process.

New Methods—Experimental and Theoretical—To Control Thin Film Properties for Target Fabrication

A new ion beam technology has been developed which allows the specific control of a number of material parameters not previously or easily controlled during thin film fabrication. The new device is a modified Kaufman ion source. The principal differences are in the design of the grids, and the fact that the gun has an open bottom structure. An additional grid has been added on the bottom to contain the plasma and force the gun to be “unidirectional.” The gun operates by forming an electron driven plasma in the center, while allowing evaporated material to pass through this plasma. When the material moves through the plasma, it may also be ionized by the Penning process, or by electron impact. The voltage of the plasma, referenced to the substrate, may be adjusted from ∼100 volts to ∼1000 volts. As the ionized plasma and deposit leave the chamber, they pass by a hot filament which provides electrons to create a charge neutral beam. Thus both insulating and conducting materials may be deposited on both insulating and conducting substrates.Another important property that can be controlled using the FTIG is the orientation of the crystal structure. Films of MgO and YSZ have been deposited in an oriented state. These cubic structures can be “forced” to a preferred 111, 220, 200, or random orientation, depending on the rate of deposit and gun voltage.A practical example of a solved problem using new modeling techniques and the Flow Through Ion Gun (FTIG) is described. The problem is to apply a platinum coating to aluminum which forms an oxide and makes film adhesion difficult with noble metals. The FTIG was used to pre-clean the inside surface, and subsequently deposit gold. Due to the aspect ratio of the cylinder, two cleaning and deposit cycles were required. Platinum distributions from an electron beam gun were used to compute a thickness uniformity on the inside of the cylinder. The uniformity was computed and measured to be ∼10% from end to end. The film microstructure was compared with thin film ballistic computations using SIMBAD, and the agreement found to be excellent.

Thin-film solid oxide fuel cell with high performance at low-temperature

A planar thin-film solid oxide fuel cell (SOFC) was developed at the Lawrence Berkeley National Laboratory – Materials Science Division. The thin-film SOFC is fabricated with an inexpensive and scalable technique involving colloidal deposition of YSZ on porous NiO–YSZ substrates, yielding SOFCs capable of high power density at an operating temperature of 800°C. The thickness of the YSZ film deposited onto the porous substrates is approximately 10 μm after sintering. Ni–YSZ/YSZ/LSM cells built with this technique have exhibited theoretical open circuit voltages (OCVs), high diffusion limited current densities and high power density. The cells have been tested for long periods of time (over 700 h) and have been thermally cycled from 600–800°C while demonstrating excellent stability over time.