Yttria-stabilized Zirconia Films Research Articles

Preparation of thin film YSZ electrolyte by using electrostatic spray deposition

Yttria-stabilized zirconia (YSZ) thin film was successfully deposited onto Ni–YSZ anode disk by the electrostatic spray deposition (ESD) technique. To deposit a dense YSZ thin film onto porous Ni–YSZ substrate, the influence of process parameter variables were examined. The relationship between process parameters and morphologies of YSZ films coated by ESD was investigated by means of SEM photography and X-ray diffraction (XRD). The result showed that dense YSZ film of average 10–15 μm thickness was deposited on the porous Ni–YSZ substrate with temperature of 400 °C, the precursor solution concentration of 0.05 M, nozzle-to-substrate distance of 30 mm, applied electric field of 18 kV, and deposition time of 90 min.

Flow and Temperature Effect on Thin Films of Yttria-Stabilized Zirconia by Sputtering.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Granular nanocrystalline zirconia electrolyte layers deposited on porous SOFC cathode substrates

Thin granular yttria-stabilized zirconia (YSZ) electrolyte layers were prepared by chemical vapor synthesis and deposition (CVD/CVS) on a porous substoichiometric lanthanum–strontium–manganite (ULSM) solid oxide fuel cell cathode substrate. The substrate porosity was optimized with a screen printed fine porous buffer layer. Structural analysis by scanning electron microscopy showed a homogeneous, granular nanocrystalline layer with a microstructure that was controlled via reactor settings. The CVD/CVS gas-phase process enabled the deposition of crack-free granular YSZ films on porous ULSM substrates. The electrolyte layers characterized with impedance spectroscopy exhibited enhanced grain boundary conductivity.

Measurement of mixed conductivity in thin films with microstructured Hebb–Wagner blocking electrodes

Determination of the ionic and electronic contributions to the total conductivity in mixed ionic–electronic conductors (MIEC) is central to understanding their properties, particularly in nanostructured ionic solids. The Hebb–Wagner blocking technique, commonly used to deconvolute ionic and electronic contributions in bulk MIECs, is susceptible to misinterpretation when applied to thin films. In this work, microfabricated electronic blocking electrodes consisting of porous Pt on dense thin yttria-stabilized zirconia (YSZ) films were applied to nanocrystalline CeO 2 thin films. The validity of the blocking structure was expressly considered with respect to alternate current and gas phase reaction pathways, with criteria developed to aid in identifying spurious effects. The ionic partial conductivity in nanocrystalline CeO 2 thin films was confirmed to be pO 2-independent while the electronic partial conductivity was found to be pO 2 dependent with a power dependence of − 0.31 ± 0.02. These results are compared with theoretical predictions of extrinsically-compensated ceria and previous results on bulk nanocrystalline ceria.

Substrate surface treatment and YSZ buffer layers by IBAD method for coated conductors

In this work, an Ion Beam Assisted Deposition (IBAD) system was utilized to fabricate Yttria-Stabilized Zirconia (YSZ) template films for coated conductors. The surface of the Hastelloy C276 substrate was modified by rolling and electropolishing. The effect of the electropolishing parameters of the substrate on the texture of the YSZ buffer layers was studied. The electropolishing current and time were optimized for short samples of 1 cm×1 cm square shape as 1 A and 60 s, respectively. And the relationship between the roughness of the substrate surface and the texture of the YSZ layer is discussed. Reel-to-reel metal tape moving apparatus was installed and used to produce meter-long buffer layer for coated conductors. The YSZ template film was deposited by IBAD method on meter-long Hastelloy tape with tape shifting speed of 15–20 m/h, and the thickness of the buffer layer was up to about 1.7 μm. The Hastelloy substrate surface was measured by Atomic Force Microscope. The thickness of the YSZ films over length was measured by Thermal Field Emission Scan Electronic Microscopy. X Ray Diffraction Ω-scan and ϕ-scan measurements were performed in order to examine the out-of-plane and in-plane texture of the YSZ buffer layers, respectively.

Ionic conductivity and thermal stability of magnetron-sputtered nanocrystalline yttria-stabilized zirconia

Thermally stable, stoichiometric, cubic yttria-stabilized zirconia (YSZ) thin-film electrolytes have been synthesized by reactive pulsed dc magnetron sputtering from a Zr–Y (80/20 at. %) alloy target. Films deposited at floating potential had a ⟨111⟩ texture. Single-line profile analysis of the 111 x-ray diffraction peak yielded a grain size of ∼20 nm and a microstrain of ∼2% regardless of deposition temperature. Films deposited at 400 °C and selected bias voltages in the range from −70 to −200 V showed a reduced grain size for higher bias voltages, yielding a grain size of ∼6 nm and a microstrain of ∼2.5% at bias voltages of −175 and −200 V with additional incorporation of argon. The films were thermally stable; very limited grain coarsening was observed up to an annealing temperature of 800 °C. Temperature-dependent impedance spectroscopy analysis of the YSZ films with Ag electrodes showed that the in-plane ionic conductivity was within one order of magnitude higher in films deposited with substrate bias corresponding to a decrease in grain size compared to films deposited at floating potential. This suggests that there is a significant contribution to the ionic conductivity from grain boundaries. The activation energy for oxygen ion migration was determined to be between 1.14 and 1.30 eV.

Epitaxial films of metals from the platinum group (Ir, Rh, Pt and Ru) on YSZ-buffered Si(1 1 1)

In the present work we have grown twin-free single crystal metal films of iridium (Ir), rhodium (Rh), platinum (Pt) and ruthenium (Ru) on silicon (1 1 1) substrates via an yttria-stabilized zirconia (YSZ) buffer layer. A prerequisite for the realisation of heteroepitaxial metal films without additional texture components was the twin-free deposition of the YSZ films by pulsed laser deposition (PLD). For the metal films on top, a novel two-step growth process was applied with an extremely low deposition rate for the first 20 nm. For all metals, a drastic texture improvement by up to a factor of 9 could be observed compared to the oxide buffer layer. Minimum values were 0.18° (Ir) and 0.12° (Rh) for tilt and twist, respectively. For all four metals investigated, twin-free epitaxial films could be grown on YSZ/Si(1 1 1) whereas the twinning problem for platinum films was solved by decoupling the Pt-YSZ interface via an additional iridium interlayer. The grown metal/YSZ/Si(1 1 1) multilayer samples offer the possibility to integrate a variety of interesting nanostructures and functional materials on silicon. They are now available in 4 in wafer size.

A novel design and performance of cone-shaped tubular anode-supported segmented-in-series solid oxide fuel cell stack

Abstract A novel design of cone-shaped tubular segmented-in-series solid oxide fuel cell (SOFC) stack is presented in this paper. The cone-shaped tubular anode substrates are fabricated by slip casting technique and the yttria-stabilized zirconia (YSZ) electrolyte films are deposited onto the anode tubes by dip coating method. After sintering at 1400 °C for 4 h, a dense and crack-free YSZ film with a thickness of about 7 μm is successfully obtained. The single cell, NiO–YSZ/YSZ (7 μm)/LSM–YSZ, provides a maximum power density of 1.78 W cm −2 at 800 °C, using moist hydrogen (75 ml min −1 ) as fuel and ambient air as oxidant. A two-cell-stack based on the above-mentioned cone-shaped tubular anode-supported SOFC is fabricated. Its typical operating characteristics are investigated, particularly with respect to the thermal cycling test. The results show that the two-cell-stack has good thermo-mechanical properties and that the developed segmented-in-series SOFC stack is highly promising for portable applications.

Low‐temperature operation of thin film solid oxide fuel cells prepared by RF magnetron sputtering

AbstractThin film solid oxygen fuel cells (SOFC) with yttria‐stabilized zirconia (YSZ) electrolyte films 3 to 12 μm thick, grown by RF magnetron sputtering on porous Ni‐YSZ cermet substrates for use as fuel electrodes, were studied to determine their power generation properties at lower operating temperatures in the vicinity of 700 °C. Single SOFCs with a YSZ electrolyte film thickness of 3 μm could be effectively operated at 800 °C and had a V–I performance measure of 700 mV–300 mA/cm2. The open circuit voltage (OCV) of the cells was nearly the same as the theoretical value. However, the OCV drop became larger as the thickness of the YSZ film was decreased, because grain boundaries and pores occurred in the film due to the surface roughness of the substrate. The voltage drop of the cells was due mainly to resistance loss in the YSZ film, and the dominance of this factor increased as the operating temperature decreased. The film conductivity at an operating temperature of 800 °C was two orders of magnitude smaller than the theoretical conductivity of the bulk electrolyte. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(6): 50–57, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10047

Low-temperature electrochemical characterization of dense ultra-thin lanthanum strontium cobalt ferrite (La0.6Sr0.4Co0.8Fe0.2O3) cathodes synthesized by RF-sputtering on nanoporous alumina-supported Y-doped zirconia membranes

Dense ultra-thin nanocrystalline La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3 (LSCF) films with thickness of ∼50 nm, have been sputtered on nanoporous anodic alumina-supported nanocrystalline thin film yttria-stabilized zirconia and patterned by photolithography into microelectrodes. This approach enables low-temperature (425–550 °C) electrochemical properties of dense ultra-thin nanocrystalline LSCF to be characterized. The results reveal that the electrochemical resistance of nanocrystalline ultra-thin LSCF is dominated by the oxygen surface exchange reaction at the electrode surface with an activation energy of 1.1 eV. Area-specific resistance of LSCF was obtained and the results are of potential relevance to utilizing nanostructured oxide cathodes for micro-SOFCs operated at low temperatures.

A comparative study of YBa2Cu3O7−δ/YSZ bilayer films deposited on silicon-on-insulator substrates with and without HF pretreatment

Highly epitaxial YBa2Cu3O7−δ (YBCO) and yttria-stabilized zirconia (YSZ) bilayer thin films have been deposited on silicon-on-insulator (SOI) substrates by using in situ pulsed laser deposition (PLD) technique. In the experiment, the native amorphous SiO2 layers on some of the SOI substrates are removed by dipping them in a 10% HF solution for 15s. Comparing several qualities of films grown on substrates with or without HF pretreatment, such as thin film crystallinity, general surface roughness, temperature dependence of resistance, surface morphology, as well as average crack spacing and crack width, naturally leads to the conclusion that preserving the native SiO2 layer on the surface of the SOI substrate can not only simplify the experimental process but can also achieve fairly high quality YSZ and YBCO thin films.

Enhancement of the crystalline quality of reactively sputtered yttria-stabilized zirconia by oxidation of the metallic target surface

Yttria-stabilized zirconia (YSZ) thin films were fabricated on glass substrates by direct current magnetron reactive sputtering. We found out that the crystalline quality of the YSZ film was improved by an oxidation process of the metallic target surface prior to the sputtering deposition process. It is speculated that, at the initial stage of the sputtering, the sputtered particles from the oxidized target surface form a layer with higher degree of crystallization on the substrate, compared with those particles from the metallic target surface. This crystallized layer can enhance the crystallization of the film deposited subsequently. Other sputtering conditions such as sputtering pressure, oxygen flow rate, substrate temperature, and Y 2O 3 content in the film were investigated, for optimization of the crystalline quality of the deposited YSZ film.

Fabrication and study on Ni 1− xFe xO-YSZ anodes for intermediate temperature anode-supported solid oxide fuel cells

Bimetal oxides Ni 1− x Fe x O ( x = 0.01, 0.04, 0.08, 0.1, 0.15, 0.2, 0.4, 0.5) were synthesized and studied as anodes for intermediate temperature solid oxide fuel cells (SOFCs) based on yttria-stabilized zirconia (YSZ) film electrolyte. A single cell consisted of Ni 1− x Fe x O-YSZ anode, YSZ electrolyte film, LSM–YSZ composite cathode was prepared and tested at the temperature from 600 °C to 850 °C with humidified hydrogen (75 ml min −1) as fuel and ambient air as oxidant. It was found that the cell with Ni 0.9Fe 0.1O-YSZ anode showed the highest power density, 1.238 W cm −2 at 850 °C, among the cells with different anode composition. The promising performance of Ni 1− x Fe x O as anode suggests that bimetal anodes are worth studied for SOFCs in future.

Preparation and characterization of sol–gel derived yttria doped zirconia coatings on AISI 316L

A stable 4 mol% yttria-stabilized zirconia (YSZ) sol has been synthesized for coating stainless steel AISI 316L for biomedical applications. The sol was prepared by controlled hydrolysis of zirconium n-butoxide using acetylacetone and nitric acid as chelating agent and catalyst, respectively. X-ray diffractograms of calcined YSZ xerogel indicated a tetragonal structure at temperature as low as 400 °C. Stainless steel was dip-coated in transparent yellow YSZ sol followed by heat treatment between 400 and 600 °C for 2 h in air. A homogeneous and crack-free YSZ film was, thus, obtained on the stainless steel surface. Adhesion strength, measured by scratch test in progressive loading sequence on coated AISI 316L, showed 27 ± 3 N critical load. Corrosion performance of the surface coating was evaluated through open-circuit potential (OCP) measurement, impedance, polarization and chronoamperometry in Ringer's solution at 37 °C. The coating enhanced the pitting potential of the substrate. The metal ions released from AISI 316L was effectively controlled by the coating.

Study of YSZ films deposited using electron-beam sputtering onto a nickel alloy with a perfect cube texture

X-ray diffraction analysis and atomic force microscopy were used to study the effect of the state of a substrate (an Ni-11 at % Cr ribbon) and deposition conditions on the texture and roughness of an yttrium-stabilized zirconia (YSZ) buffer layer deposited by electron-beam sputtering. The presence of a sharp cube texture in the nickel-alloy ribbon was shown to be insufficient condition for obtaining a biaxial texture in the YSZ film. A two-dimensional (2 × 2) sulfur superstructure should be formed on the nickel-ribbon surface. In this case, the YSZ film with a sharp {100} 〈100〉 cube texture and surface roughness of ∼10–15 nm can be prepared at a low deposition rate of 0.005–0.008 nm/s and a substrate temperature of 700–800°C.

Performance evolution of NiO/yttria-stabilized zirconia anodes fabricated at different compaction pressures

Nickel oxide (NiO)/yttria-stabilized zirconia (YSZ) anode substrates were fabricated at four compaction pressures, 70, 200, 500 and 1000 MPa, the particle size distributions of NiO and YSZ were investigated with the powders treated at different compaction pressures, and the effects of compaction pressure on the performance of anodes with and without pore-formers were investigated by studying the effects of compaction pressure on the sintering shrinkage, compaction density, sintered density and electrical conductivity of anodes and the performance of cells. Experimental results demonstrated that the mismatch in the sintering shrinkages of YSZ films and the anodes compacted at 70 and 1000 MPa caused gas leakage across the films and thus a higher local temperature than the furnace temperature. The single cell with the anode using pore-former and compacted at 500 MPa exhibited the best output performance of 2.66 W cm −2 at 800 °C.

Nanostructure characterization in single and multi layer yttria stabilized zirconia films using XPS, SEM, EDS and AFM

Single and multiple layers of yttria partially stabilized zirconia (6Y-TZP) nanostructured films were deposited on 304 stainless steel substrate by an electrochemical deposition method. This technique is considered to be an important tool in the formation of nanostructured materials, including monolayer and multilayer films, powders and composites. The aim of the work reported in this paper is the codeposition of two hydroxides, Zr(OH) 4 and Y(OH) 3, in order to obtain yttria partially stabilized ziconia film, and the preparation of monolayer and multilayer ceramic film of 6Y-TZP. To examine the structure and composition of one layer and three layers of 6Y-TZP deposited on 304 stainless steel, several experimental techniques were used: XPS, XRD, SEM, TEM, EDS and AFM. The XPS technique revealed that zirconia and yttria were present in solid solution. This result was corroborated by XRD. SEM and TEM showed that nanostructured uniform and homogeneous films were obtained. AFM results verified that no deep cracks reached the substrate surface and that little roughness was present on the films.

Pulsed laser deposition of the yttria-stabilized zirconia films

Yttria-stabilized zirconia (YSZ) films are of considerable interest in optical, electronic and aerospace community and multitude of fabrication techniques are reported in the literature. This paper reports the characteristics of the YSZ films produced by pulsed laser deposition technique using a KrF excimer laser with yttria-stabilized zirconia targets. Morphological characteristics of the YSZ films were investigated by atomic force microscope (AFM) and scanning electron microscope. Distinct peak and valley structures with height differences in the range of 10–30 nm were observed in AFM images of the YSZ film surfaces, and measured roughness was 3.5–6.5 nm. A nanoindenter was used to investigate mechanical properties of the films deposited at different chamber pressure. Measured hardness and Young's modulus were about 10–11 GPa and 86–95 GPa respectively. Elemental composition and structural characteristics of the YSZ films were analyzed by electron prove micro-analyzer and X-ray diffraction, respectively.

Thin porous Ni–YSZ films as anodes for a solid oxide fuel cell

Porous Ni–YSZ (YSZ—yttria-stabilized zirconia) films were fabricated by reactive co-sputtering of a Ni and a Zr–Y target, followed by sequentially annealing in air at 900 °C and in vacuum at 800 °C. The Ni–YSZ films comprised small grains and pores that were tens of nanometers in size. The porous Ni–YSZ films were used as an anode on one side of a YSZ electrolyte disc and a La 0.7Sr 0.3MnO 3 thick film was used as a cathode on the other side of the disc to form solid oxide fuel cells (SOFCs). The voltage–current curves of the SOFCs with single- and a triple-layered porous anodes were measured in a single-chamber configuration, in a mixture of CH 4 and air (CH 4:O 2 volume ratio=2:1). The maximum power density of the SOFC using the single-layered porous Ni–YSZ thin films as the anode was 0.38 mW cm −2, which was lower than that of 0.76 mW cm −2, obtained using a screen-printed Ni–YSZ thick anode. The maximum power density of the SOFC with a thin anode was increased, but varied between 0.6 and 1.14 mW cm −2 when a triple-layered porous Ni–YSZ anode was used.

Microstructure of Nanocrystalline Yttria‐Doped Zirconia Thin Films Obtained by Sol–Gel Processing

Nano‐ and microcrystalline yttria‐stabilized zirconia (YSZ) thin films with a dopant concentration of 8.3±0.3 mol% Y2O3 were prepared with a variation in grain size by two orders of magnitude. A sol–gel‐based method with consecutive rapid thermal annealing was applied to fabricate YSZ films, resulting in about 400 nm YSZ on sapphire substrates. The average grain sizes were varied between 5 nm and 0.5 μm by heat treatment in the temperature range of 650°–1350°C for 24 h. High‐resolution (HRTEM) and conventional transmission electron microscopy analyses confirmed specimens—irrespective of the thermal treatment—consisting of cubic (c‐)ZrO2 grains with nanoscaled tetragonal precipitates coherently embedded in the cubic matrix. Energy‐dispersive X‐ray spectroscopy and HRTEM on a large number of specimens yielded a homogeneous yttria concentration within the grains and at the grain boundaries with the absence of impurities, i.e. silica at the grain boundaries.