YSZ Films Research Articles

Characterization of Thin-Film YSZ Deposited via EB-PVD Technique in Anode-supported SOFCs

An anode-supported solid oxide fuel cell (SOFC) based on yttria-stabilized zirconia (8YSZ) electrolyte that was deposited via an electron-beam physical vapor deposition (EB-PVD) technique, was investigated. A NiO-8YSZ plate was used as both an anode substrate and as a substrate for the deposition of 8YSZ. An additional buffering layer was coated on the anode substrate via a screen printing before the deposition of YSZ film in order to enhance the surface smoothness for the film deposition. In this study, we controlled various experimental variables for the film deposition and subsequent heat treatment process to obtain highly dense and impervious electrolyte film. Consequently, we were able to obtain a large area and dense YSZ film with a uniform thickness of . The surface and cross-sectional microstructure and the corresponding phase of deposited film were thoroughly analyzed by scanning electron microscopy and X-ray diffraction. The electrochemical performance of the EB-PVD unit cell was investigated using dc current-voltage load testing, a dc current interruption technique, and an ac-impedance spectroscopy. Peculiar microstructural features of the deposited film, such as the columnar structure of grains along the growing axis, and the film’s microstructural effect on unit cell performance, were addressed.

Conductivity Switching Behaviors in ZrO<sub>2</sub> and YSZ Films Deposited by Pulsed Laser Depositions

Polycrystalline ZrO2 and yttria-stablilized ZrO2 thin films have been deposited on Pt/Ti/SiO2/Si substrates by pulsed laser deposition methods. Pt/ZrO2/Pt and Pt/YSZ/Pt capacitor structures show giant conductivity switching behaviors which can be utilized for nonvolatile memory devices. Maximum on/off ratio of 106 and good endurance even after 105 times conductivity switching are observed in a typical Pt/ZrO2/Pt whose ZrO2 film has been deposited at 100 °C and an oxygen pressure of 50 mTorr. The Pt/ZrO2/Pt structure exhibits two ohmic behaviors in the low voltage region (V < 1.4 V) depending on the value of previously applied high voltage and Schottky-type conduction in the high voltage region (1.4 V < V < 8.9 V). It seems that conductivity switching behaviors in our Pt/ZrO2/Pt structure result from the changes in both the Schottky barrier and the bulk conductivity controlled by applied voltages. A Pt/YSZ/Pt capacitor structure has more stable reset voltage and current state than a Pt/ZrO2/Pt capacitor structure. Moreover, a Pt/YSZ/Pt capacitor structure shows higher Conductivity than a Pt/ZrO2/Pt capacitor structure, which may result from substitution of Y3+ ions for Zr4+ ions.

Growth and electrical conductivity of thin film YSZ by puled laser deposition

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Screen-printed thin YSZ films used as electrolytes for solid oxide fuel cells

A thin yttria-stabilized zirconia (8 mol% YSZ) film was successfully fabricated on a NiO-YSZ anode substrate by a screen-printing technique. The scanning electron microscope (SEM) results suggested that the YSZ film thickness was about 31 μm after sintering at 1400 °C for 4 h in air. A 60 wt% La 0.7Sr 0.3MnO 3 + 40 wt% YSZ was screen-printed onto the YSZ film surface as cathode. A single cell was tested from 650 to 850 °C using hydrogen as fuel and ambient air as oxidant, which showed an open circuit voltage (OCV) of 1.02 V and a maximum power density of 1.30 W cm −2 at 850 °C. The OCV was higher than 1.0 V, which suggested that the YSZ film was quite dense and that the fuel gas leakage through the YSZ film was negligible. Screen-printing can be a promising method for manufacturing YSZ films for solid oxide fuel cells (SOFCs).

전자빔 물리증착을 이용한 고체 산화물 연료전지의 제조 : I. YSZ 박막 전해질의 제조

Electron Beam Physical Vapor Deposition (EB-PVD) was applied to fabricate a thin film YSZ electrolyte with large area on the porous NiO-YSZ anode substrate. Microstructural and thermal stability of the as-deposited electrolyte film was investigated via SEM and XRD analysis. In order to obtain an optimized YSZ film with high stability, both temperature and surface roughness of substrate were varied. A structurally homogeneous YSZ film with large area of 12 × 12 ㎠ and high thermal stability up to 900℃ was fabricated at the substrate temperature of T s /T m higher than 0.4. The smoother surface was proved to give the better film quality. Precise control of heating and cooling rate of the anode substrate was necessary to obtain a very dense YSZ electrolyte with high thermal stability, which affords to survive after post heat treatment for fabrication a cathode layer on it as well as after long time operation of solid oxide fuel cell at high temperature.

Synthesis and characterization of nanocrystalline (Zr0.84Y0.16)O1.92–(Ce0.85Sm0.15)O1.925 heterophase thin films

A new type of nanocrystalline samarium-doped-ceria/yttrium-stabilized-zirconia (SDC/YSZ) heterophase thin film electrolytes was synthesized on MgO and Si substrates by spin coating and thermal treatment of SDC-nanoparticle-incorporated polymeric precursors. In the heterophase films, SDC nanoparticles were uniformly dispersed in a nanocrystalline YSZ matrix. The heterophase structure was stable when fired in air at temperatures up to 850 °C. The nanocrystalline heterophase thin films exhibited electrical conductivities significantly higher than that of the phase-pure YSZ and SDC nanocrystalline thin films at reduced temperatures. The effects of SDC grain size and volume fraction on the electrical conductivity of the heterophase films were also studied.

Mixed potential NO x sensors using thin film electrodes and electrolytes for stationary reciprocating engine type applications

Mixed potential sensors using dense, thin film metal oxide working electrodes, Pt counter electrodes, and thin film YSZ electrolytes on Al 2O 3 polycrystalline and sapphire substrates were prepared and studied between 450 and 650 °C. Their response to NO, NO 2, CO, and C1 and C3 hydrocarbons in 10.4% O 2/N 2 balance and in air atmospheres was characterized. The lanthanum chromite-based sensors showed preferential sensitivity to NO 2 with cross sensitivity to CO and non-methane hydrocarbons such as C 3H 6 and C 3H 8 with the highest NO x sensitivity and minimal CO/HC cross sensitivity exhibited by a sensor prepared with a La 0.8Sr 0.2CrO 3 working electrode. Studies of the Mg-doped LaCrO 3 devices conducted for up to 800 h at 600 °C showed minimal aging in these devices. In contrast, sensors fabricated with spinel NiCr 2O 4 or ZnFe 2O 4 working electrodes showed preferential sensitivity to HCs and minimal sensitivity to NO 2. Sensors fabricated with Y 0.16Tb 0.3Zr 0.54O 2− ∂ working electrodes required operating temperatures in excess of 600 °C and, like the spinels, showed minimal NO x sensitivity. A prototype three-electrode mixed potential device for the detection of multiple gases was also demonstrated. The use of a heated Pt black pre-catalyst upstream to the sensor was demonstrated to effectively remove the CO and hydrocarbon response.

Fabrication of Crystallized Si Film Deposited on a Polycrystalline YSZ Film/Glass Substrate at 500°C

AbstractWe used a polycrystalline YSZ film deposited on the quartz substrate as a seed layer to enhance crystallization of the Si film deposited on it. The YSZ film was deposited by reactive sputtering at less than 50°C and the preferential orientation was (111). The 60-nm-thick Si film was deposited by e-beam evaporation method on the substrate with and without the YSZ film. It was found that the crystallization of the Si film deposited on the YSZ film occurs but not without the YSZ film at the temperature of 515°C. The SEM image of the Secco-etched Si film showed that the crystallized Si film consisted of ~50-nm-size grains and, from the TEM image, it is supposed that the Si grains are grown directly from the YSZ film.

Effect of starting powder on screen-printed YSZ films used as electrolyte in SOFCs

Screen-printing technology was developed to fabricate dense YSZ electrolyte films onto NiO–YSZ porous anode substrates. A single fuel cell of Ni-YSZ/YSZ (31 μm)/LSM-YSZ was successfully prepared by screen-printing technology. Using humidified hydrogen as fuel and ambient air as oxidant, the fuel cell provided the maximum power densities of 0.18, 0.33, 0.58, 0.97 and 1.3 W/cm 2 at 650, 700, 750, 800 and 850 °C, respectively. The properties of the starting YSZ powder exerted a significant effect on the characteristics of the screen-printed YSZ electrolyte films. The aggregates of the powder could be partially broken by ball milling. The YSZ powder with a small particle size and a narrow particle size distribution helped to obtain dense YSZ films. The films prepared from the YSZ powder with high aggregates were very porous, which resulted in a low open circuit voltage, a high ohmic resistance, a high polarization resistance and thus a poor cell performance.

R.F. SPUTTERING DEPOSITION OF BUFFER LAYERS FOR Si/YBCO INTEGRATED MICROELECTRONICS

The aim of the present work is the optimization of the Si /buffer-layer/YBCO multilayer deposition process so as to grow superconducting films of quality suitable for device applications. The structural properties of the Si/CeO 2 system, obtained by RF magnetron sputtering of CeO 2 targets in Ar atmosphere, have been studied. More than 50 films have been deposited and some of them submitted to post-deposition annealing treatments both in N 2 and O 2 atmospheres. The presence of an unwanted amorphous SiO 2 layer at the Si/CeO 2 interface compromises the YBCO c-axis orientation, and therefore the sharpness of the R versus T transition. A newly designed deposition system has been realized: it has been specially conceived for obtaining bi- and tri-layers, adopting two targets in YSZ and CeO 2, respectively. Results on YSZ/Si and CeO 2/ YSZ/Si systems obtained with the new machine are presented and discussed: (100) oriented YSZ films with nominal thickness of 40 nm have been obtained. The CeO 2 film subsequently deposited has the desired (100) orientation. The YBCO film, in the final YBCO/YSZ/CeO 2/ Si configuration, is c-axis oriented.

Yttria-stabilized zirconia films of different composition as buffer layers for the deposition of epitaxial diamond/Ir layers on Si(001)

Diamond/iridium/yttria-stabilized-zirconia (YSZ)/silicon is a promising multilayer structure for the future realization of single crystal diamond wafers. In the present work we studied the heteroepitaxial growth of YSZ films on Si(001) prepared by pulsed laser deposition. Films deposited from three ablation targets with different yttrium content were compared systematically. Depending on the specific target purely c-axis oriented tetragonal or cubic films were obtained. The films were epitaxial with a low mosaicity of about 1°. Iridium layers deposited on top by e-beam evaporation showed a perfect cube-on-cube epitaxial alignment on all types of YSZ films. The iridium films exhibit a smooth surface with only few holes. All the multilayer structures were stable in subsequent diamond nucleation processes via bias enhanced nucleation (BEN).

Oxygen detection using yttria-stabilized zirconia thin films doped with platinum

Abstract Yttria stabilized zirconia (YSZ) thin films are obtained using both spray-pyrolysis and dip-coating. The ability of YSZ films incorporated with platinum nanospecies (Pt-YSZ) to detect oxygen is compared with that of pure YSZ thin films using a new experimental setup. With this system, the surface electrical resistance of the films as a function the oxygen content is measured at a fixed temperature. In addition, the effects of thermal annealing on the oxygen sensitivity of the films are observed. Platinum doped samples, Pt-YSZ, show different kinetics of carrier diffusion as compared to pure YSZ samples.

졸-겔법을 이용한 고체산화물연료전지의 전해질 박막 제조 및 가스 투과도

In this study, thin electrolyte layer was prepared by 8YSZ (8 mol% Yttria-Stabilized Zirconia) slurry dip and sol coating onto the porous anode support in order to reduce ohmic resistance. 8YSZ polymeric sol was prepared from inorganic salt of nitrate and XRF results of xerogel powder exhibited similar results (99.2±1 wt%) compared with standard sample (TZ-8YS, Tosoh Co.). The dense and thin YSZ film with 1 μm thickness was synthesized by coating of 0.7 M YSZ sol followed by heat-treatment at 600℃ for 1 h. Thin film electrolyte sintered at 1400℃ showed no gas leakage at the differential pressure condition of 3 atm.

Thick YSZ films prepared via a modified sol–gel route: Thickness control (8–80 μm)

Dip-coated suspensions were used for preparing YSZ layers on both dense and porous substrates. The microstructure of the as-obtained thick films was studied by varying the characteristics of the organic YSZ suspensions (concentration, viscosity, etc.) used as coating bath. The thickness and the microstructure of the films were found to depend on the YSZ powder content and on the polymeric sol/dispersant solution (EtOH–MEK) ratio of the suspensions. The porosity created in the films depends on the r m ratio, e.g., the volume fraction of polymeric chains in the green layers. Finally, a comparison of the film thickness on dense and porous substrates showed that films prepared on porous substrates tend to exhibit higher thicknesses. Accordingly, YSZ ceramic films with thickness varying in between 8 and 80 μm were prepared.

Electrical Properties of ZrO2 and YSZ Films Deposited by Pulsed Laser Deposition

Polycrystalline ZrO2 and yttria-stabilized ZrO2 thin films have been deposited on Pt/Ti/SiO2/Si substrates by pulsed-laser-deposition methods. Pt/ZrO2/Pt and Pt/YSZ/Pt capacitor structures show giant conductivity switching behaviors which can be utilized for nonvolatile memory devices. Maximum on/off ratio of 10 and good endurance even after 10 times conductivity switching are observed in a typical Pt/ZrO2/Pt whose ZrO2 film has been deposited at 100 ◦C and at an oxygen pressure of 50 mTorr. The Pt/ZrO2/Pt structure exhibits two ohmic behaviors in the low-voltage region (V < 1.4 V), depending on the value of previously applied high voltage, and Schottky-type conduction in the high-voltage region (1.4 V < V < 8.9 V). It seems that conductivity switching behaviors in our Pt/ZrO2/Pt structure result from changes in both the Schottky barrier and the bulk conductivity controlled by applied voltages. A Pt/YSZ/Pt capacitor structure has more stable reset voltage and current state than a Pt/ZrO2/Pt capacitor structure. Moreover, a Pt/YSZ/Pt capacitor structure shows higher conductivity than a Pt/ZrO2/Pt capacitor structure, which may result from substitution of Y ions for Zr ions.

Evaluation of crystallinity and film stress in yttria-stabilized zirconia thin films

Yttria (3 mol %)-stabilized zirconia (YSZ) thin films were deposited using radio frequency (rf) magnetron sputtering. The YSZ thin films were deposited over a range of temperatures (22–300 °C), pressures (5–25 mTorr), and gas compositions (Ar∕O ratio). Initial studies characterized a select set of properties in relation to deposition parameters including: refractive index, structure, and film stress. X-ray diffraction (XRD) showed that the films are comprised of mainly monoclinic and tetragonal crystal phases. The film refractive index determined by prism coupling, depends strongly on deposition conditions and ranged from 1.959 to 2.223. Wafer bow measurements indicate that the sputtered YSZ films can have initial stress ranging from 86 MPa tensile to 192 MPa compressive, depending on the deposition parameters. Exposure to ambient conditions (25 °C, 75% relative humidity) led to large increase (∼100MPa) in the compressive stress of the films. Environmental aging suggests the change in compressive stress was related to water vapor absorption. These effects were then evaluated for films formed under different deposition parameters with varying density (calculated packing density) and crystal structure (XRD).

Free-standing epitaxial La1−x(Sr,Ca)xMnO3 membrane on Si for uncooled infrared microbolometer

Ar ion beam etching and inductively coupled SF6 and C4F8 plasma-etching processes have been employed to fabricate free standing membrane from the heteroepitaxial La1−x(Sr,Ca)xMnO3(50nm)∕Bi4Ti3O12(100nm)∕CeO2(40nm)∕YSZ(30nm) film structure pulsed laser deposited on Si(001) wafer. We demonstrate feasibility to use epitaxial colossal magnetoresistive manganite film as thermally isolated self-supporting membrane for uncooled infrared microbolometer applications.

Spray pyrolysis deposition of YSZ and YSZ–Pt composite films

In the present paper procedures are described for spray pyrolysis deposition of YSZ films (0.1–30 μm in thickness) with 8 or 15 mole % of YO 1.5 on different substrates. Aqueous or ethylene glycol solutions of Y–Zr-citrates were used as starting material and O 2 as carrier gas. The crystal structure and the morphology of the films were studied. The optimal deposition and post-deposition annealing conditions were defined, taking into account the desired film thickness and characteristics. Substrate temperatures of 250 °C during the deposition followed by heating for 10 min to 400 °C after every spraying and to 590 °C after every three sprayings with final annealing at 590 °C for 2 h in static air atmosphere were found to be suitable for the production of dense, uniform and cracks-free films.

Effect of NiO/YSZ compositions on the co-sintering process of anode-supported fuel cell

Effect of NiO/YSZ compositions on the co-sintering process of anode-supported fuel cell was researched. The green YSZ layer was fabricated by modifying electrostatic powder coating, and the relative density is about 52%. After co-firing at 1400 °C for 5 h, the sample of YSZ film based on the 1000-NY support (pre-calcinated NiO 60 wt.%, YSZ 40 wt.%) is concave due to the mismatch of shrinkages between the YSZ film and anode support and there exist cracks on the film. Dense YSZ films based on the NY-20P (NiO 48 wt.%, YSZ 32 wt.% and graphite 20 wt.%) support were fabricated after co-firing at 1400 °C for 2 h. The OCV and the peak power density of a single cell with a 15 μm thick YSZ film based on the NY-20P support are 1.09 V and 315 mW/cm 2 at 800 °C, respectively.

Fabrication, characterisation and application of (8 mol% Y2O3) ZrO2 thin film on Na3Zr2Si2PO12 substrate for sensing CO2 gas

A planar type CO2 gas sensor employing (8 mol% Y2O3) ZrO2 (YSZ) thin film on Na3Zr2Si2PO12 (Nasicon) substrate with Na2CO3 as an auxiliary electrode has been fabricated and tested in laboratory environment between 700–900 K. The YSZ thin film was fabricated on Nasicon and alumina substrate using radio frequency (RF) magnetron sputtering. The film was examined using SEM and X-ray diffraction (XRD) after treating the Nasicon-YSZ bi-layer structure at 1300 K for 2 h. The results indicate that a crack free YSZ film was produced on Nasicon surface that was well bonded to the substrate. The conductivity of sputtered YSZ thin film measured by ac-impedance spectroscopy has been found to be higher than that of YSZ pellet by approximately half an order of magniture. The bi-electrolyte planar sensor displays rapid response (t95≤ 200 s) to CO2 compared to the tube type sensor (t95≤ 700 s) and the measured open circuit voltage of the electrochemical CO2 sensor has been found to be Nernstian at all temperatures.