Zirconia Films Research Articles

The Production and Characterization of Ytterbium‐Stabilized Zirconia Films for SOFC Applications

(ZrO2)1–x(Yb2O3)x binary systems were investigated in the doping range of 0.02 ≤ x ≤ 0.12. Ytterbium‐doped zirconia powders were synthesized using the Pechini method. X‐ray diffraction (XRD) measurements showed that fcc ZrO2 was stabilized for 8–12 mol% Yb‐doping rate. The produced Yb‐stabilized Zr (YbSZ) films were characterized; their thickness and homogeneity properties depended on the nature of the YbSZ slurry. All coating parameters were optimized and determined with precoating treatments. The samples were characterized by differential thermal analysis/thermal gravimetry (DTA/TG), scanning electron microscopy (SEM) and ac impedance measurements.

Structure and Electroactivity of Tungsten Oxides in Acid Medium: Enhancement of Charge Propagation Rates through Nanostructuring and Formation of Mixed-Metal Oxide Systems

Electrochromism in tungsten oxides and related systems has been recognized for long time and has been still of interest for display applications. Redox transitions and related reversible coloration of thin WO3 films are believed to be controlled by simultaneous injection or removal of electrons and protons. The dynamics of partial reduction (in acid medium) of transparent tungsten(VI) oxides to blue hydrogen tungsten(VI,V) oxide bronzes or lower tungsten(VI,IV) oxides is largely dependent of the oxide morphology, nanostructuring, degree of hydration, or population of colored W(VI,V) or W(VI,IV) sites. For example, by depositing nanorods of tungsten oxide, rather than conventional tungsten oxide, on the ITO conducting glass (or the inert glassy carbon) substrate, the enhancement in the degree of the system's voltammetric reduction in acid medium (0.5 M H2SO4) has been observed. Tungsten oxide nanorods seem to be partially and reversibly reduced not only to nonstoichiometric hydrogen tungsten(VI,V) oxide bronzes (HxWO3, 0<x<1) but also substoichiometric lower tungsten (VI,IV) oxides (WO3-y, 0<y<1). Another important issue is the mobility and availability of protons within the tungsten oxide film. We have found that by controlled admixing of tungsten oxide with zirconia nanoparticles both nanostructured morphology and high mobility of protons can be adjusted. The resulting mixed (hybrid or composite) system is well-behaved: redox reactions (which are characteristics of WO3) are fast and reversible despite the presence of semiconducting zirconia (ZrO­2). While ZrO2 is not electroative, WO3 undergoes redox reactions leading to formation of partially reduced hydrogen bronzes (H x WO3) in which mobility of H+ is coupled to electron transfers. The composite material is stabilized through electrostatic attraction between positively charged zirconium oxo cations (ZrO2+, ZrOH3+, [Zr3(OH)4]3+) and anionic tungstates (WO4 2- in WO3*H2O or H2WO4). Among important issues are: high population of hydroxyl groups and high mobility of protons at surfaces of zirconia (ZrO2) nanostructures in addition to the existence of fast electron transfers coupled to proton displacements in partially reduced tungsten oxides (HxWO3). In a different series of chronocoulometric experiments, diffusion coefficients (for charge propagation) have been determined, and they have been found typically higher for hybrid mixed metal (tungsten(VI)/zirconium(IV) oxide films (close to 10-7 cm s-1). Mechanistic considerations and the results of spectroelectrochemical and diagnostic spectroscopic (e.g. FTIR) experiments will also be provided. We acknowledge collaboration with Christian Perruchot and Mohamed Jouini from ITODYS, Université Paris Diderot, France.

Study of thin films of yttria-stabilized zirconia (YSZ) for the oxidation of some volatile organic compounds

Thin films of YSZ and 1%Pt/YSZ were deposited onto stainless steel tubes by an electrophoretic deposition technique. O2-TPD from r.t. to 600°C using induction heating was used to characterize the two films considering (i) the amount of oxygen desorbed (5.1 and 1.4×10−2μmolO2·g−1 for 1%Pt/YSZ and YSZ respectively) and (ii) the apparent activation energy of desorption Eapp. Finally, complete oxidation of some VOCs (isopropanol and toluene) in air was studied on both films. From r.t. to 400°C, oxidation of isopropanol can be achieved with either YSZ or 1%Pt/YSZ but only this last catalyst can achieve the complete oxidation of toluene.

CERAMIC THIN FILMS REALIZED BY MEANS OF PULSED PLASMA DEPOSITION TECHNIQUE: APPLICATIONS FOR ORTHOPEDICS

Joint prosthesis are usually subjected to several failing mechanisms, including wear of the ultra-high molecular weight polyethylene (UHMWPE) insert. The main goal of this study was to assess the possibility to improve the tribological properties of titanium component by depositing zirconia thin films on its surface by pulsed plasma deposition (PPD) method. Zirconia-coated titanium spheres were tested against UHMWPE disks, both in dry and wet conditions. Zirconia films exhibited a homogenous sub-micrometric grain size distribution and low roughness. Interestingly, zirconia-coated titanium spheres showed lower wear rate of the UHMWPE component, compared to uncoated titanium spheres, supporting the feasibility of the proposed approach.

Defective interfaces in yttrium-doped barium zirconate films and consequences on proton conduction.

Yttrium-doped barium zirconate (BZY) thin films recently showed surprising electric transport properties. Experimental investigations conducted mainly by electrochemical impedance spectroscopy suggested that a consistent part of this BZY conductivity is of protonic nature. These results have stimulated further investigations by local unconventional techniques. Here, we use electrochemical strain microscopy (ESM) to detect electrochemical activity in BZY films with nanoscale resolution. ESM in a novel cross-sectional measuring setup allows the direct visualization of the interfacial activity. The local electrochemical investigation is compared with the structural studies performed by state of art scanning transmission electron microscopy (STEM). The ESM and STEM results show a clear correlation between the conductivity and the interface structural defects. We propose a physical model based on a misfit dislocation network that introduces a novel 2D transport phenomenon, whose fingerprint is the low activation energy measured.

The effects of deuteration on the nanostructured zirconium films deposited by pulsed laser deposition for nuclear fusion applications

In this paper, zirconium films have been deposited on Al2O3 (0001) substrates by pulsed laser deposition (PLD) and then transferred to deuterium atmospheres. We find that the formation of Zr0.38D0.62 is under the deuterated temperatures of 923K. The surface morphologies, electrical features and optical properties of as-grown zirconium films and zirconium deuteride films are systematically investigated as a function of three pulse repetition rates. It is found that the zirconium films show very smooth surfaces and high specular reflectivity. Moreover, exposure of the as-deposited zirconium films to deuterium atmospheres revealed that some pits formed on the surface of films. These defects induced by deuterium make the specular reflectivity and resistance of films change. The results of our investigation will be useful to optimize the environmental conditions for the First Mirror application in fusion devices.

Structural and Mechanical Properties of Zirconia Film Deposited by Plasma Focus Device

Nano-crystalline ZrO2/ZrSiO4 composite films are deposited on Si by the irradiation of energetic oxygen ions by plasma focus operation. The XRD patterns confirm the development of different phases (ZrO2 and ZrSiO4) which grow along various orientations and their peak intensities strongly depend on increasing focus shots and sample angular positions. The average crystallite size of the films deposited at 0° angular position is increased with increasing focus shots while it is decreased for the films deposited at 10° angular position. The dislocation density in ZrSiO4 (2 0 4) plane is increased from 3.51 × 10−5 to 8.67 × 10−5 (nm)−2 while it is decreased from 8.85 × 10−5 to 0.011 × 10−5 (nm)−2 in m-ZrO2 (1 2 3) plane when the samples are treated at 0° and 10° angular positions for five focus shots respectively. The FESEM analysis confirms the formation of rounded nano-particles, complicated network of nano-rods, formation of compact, uniform and smooth multi-layers. The EDS analysis confirms the presence of Si, Zr and O in the composite films deposited for different focus shots and sample angular positions. The maximum microhardness of the composite film deposited for 25 focus shots is found to be 10.56 ± 0.51 GPa which definitely will improve the life time of the coated material.

Application of 8YSZ Nanopowder Synthesized by the Modified Solvothermal Process for Anode Supported Solid Oxide Fuel Cells

Thin electrolyte yttria-stabilized zirconia (8YSZ) films were coated on the porous solid oxide fuel cell (SOFC) anode substrates for the use at an intermediate temperature range. Nano-8YSZ powder with a particle size of about 5 nm was synthesized using the modified solvothermal process. The electrolyte suspension was prepared by dispersion the synthesized 8YSZ nanopowder in ethanol, with PVB and 1,3-propanediol as a binder and a charging agent respectively. The 8YSZ suspension was subsequently deposited on the pre-sintered NiO-YSZ porous substrates by the electrophoretic deposition (EPD) technique. In order to obtain high quality electrolyte films, preparation process was optimized through two strategic approaches; (i) adjustment of suspension's rheological property and (ii) compatibility of anode-electrolyte sintering shrinkage. Rheological property of the suspension was improved with an addition of 1,3-propanediol. The zeta potential of this suspension was increased and reached the value of +24 mV so the well-dispersed slurry was finally obtained. The second approach was achieved by using a proper composite anode powders. Dense and uniform 8YSZ electrolyte films with a thickness of about 1 thickness successfully be formed on the NiO-YSZ porous substrates after co-sintering at 1400 °C for 2 h.

Investigation of deposition rate, liquid droplets and surface morphology of zirconium films deposited by pulsed laser ablation

The effects of laser fluence on the surface morphology of zirconium films grown onto Si (100) by pulsed laser deposition are investigated. We found that the average nanoparticle size and the root mean square (RMS) roughness of Zr films increase with increasing laser fluence. The presence of droplets on the surface of deposited films, which is one major shortcoming of pulsed laser deposition (PLD), was studied at different laser fluences, pulse repetition rates, and substrate temperatures. In this paper, the distribution of droplets was well investigated in detail. In order to have more control of the deposition process, we investigate the influence of deposition time, laser fluence, and pulse repetition rate on the deposition rate. The research work in this paper lays the foundation for further obtaining the fine characteristics of Zr thin films.

Blister defect formation within partially stabilized zirconia film during constrained sintering

Yttria stabilized zirconia (YSZ) film has been screen printed and sintered on a rigid substrate. The constrained sintering caused the formation of multiple microcracks and most critically large “blister” defects. The morphology of such defects has been characterized by scanning electron microscopy (SEM). It was revealed that the film surface exhibits noticeable roughness. Microhardness testing revealed little variation in green density distribution. Rheological measurement, however, showed that some agglomerations are present in the YSZ ink. The existence of agglomerations in the screen printing ink in combination with debonding at the film/substrate interface is potentially the cause for the formation of blister defects.

Growth of an Ultrathin Zirconia Film on Pt3Zr Examined by High-Resolution X-ray Photoelectron Spectroscopy, Temperature-Programmed Desorption, Scanning Tunneling Microscopy, and Density Functional Theory.

Ultrathin (∼3 Å) zirconium oxide films were grown on a single-crystalline Pt3Zr(0001) substrate by oxidation in 1 × 10–7 mbar of O2 at 673 K, followed by annealing at temperatures up to 1023 K. The ZrO2 films are intended to serve as model supports for reforming catalysts and fuel cell anodes. The atomic and electronic structure and composition of the ZrO2 films were determined by synchrotron-based high-resolution X-ray photoelectron spectroscopy (HR-XPS) (including depth profiling), low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. Oxidation mainly leads to ultrathin trilayer (O–Zr–O) films on the alloy; only a small area fraction (10–15%) is covered by ZrO2 clusters (thickness ∼0.5–10 nm). The amount of clusters decreases with increasing annealing temperature. Temperature-programmed desorption (TPD) of CO was utilized to confirm complete coverage of the Pt3Zr substrate by ZrO2, that is, formation of a closed oxide overlayer. Experiments and DFT calculations show that the core level shifts of Zr in the trilayer ZrO2 films are between those of metallic Zr and thick (bulklike) ZrO2. Therefore, the assignment of such XPS core level shifts to substoichiometric ZrOx is not necessarily correct, because these XPS signals may equally well arise from ultrathin ZrO2 films or metal/ZrO2 interfaces. Furthermore, our results indicate that the common approach of calculating core level shifts by DFT including final-state effects should be taken with care for thicker insulating films, clusters, and bulk insulators.

Stress and Phase Engineered ZrO2/Ge for High-k Dielectric Applications

ABSTRACTZrO2/Ge is potential high-k dielectric candidate to replace silicon based devices. Controlling stress in zirconia film and stabilizing high dielectric constant phase is crucial for high-k application. A precise control of stress and phase selectivity in high-k thin films is demonstrated. Thin films of ZrO2 were grown by reactive sputter deposition. Wide range of growth stress in thin films from -0.3 to -2.8 GPa can be tuned by growth rate control. Adatom incorporation into grain boundary was the dominant source of observed stress. Phase selectivity in zirconia was achieved by tuning growth parameters.

ALD Zirconium Oxide (ZrO2) Thin Films Mechanical/Structural Properties for High-Tech Applications

The nanomechanical and structural properties of atomic layer deposition (ALD) zirconium oxide (ZrO2) films of varying thickness deposited on p-type Si (100) substrates with 200, 300, and 500, ALD deposition cycles were investigated. The 300 ALD deposition cycles ZrO2 films were further annealed at 600°C. The nanomechanical properties of the films were tested using nanoindentation and the surface morphology was investigated using AFM. The structural and surface properties were explored using field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). We discuss the influence of the deposition technique on the structure and properties of the ZrO2 films resulting from ALD synthesis. The nanoindentation results indicate that the films become consistently softer as the number of ALD deposition cycles increase and the film grows thicker. Further annealing of the films at 600°C slightly enhanced the hardness and fracture toughness of the films. The annealed ALD films depicted shorter radial cracks compared to the films under the same applied stress, which were not annealed in forming gas.

Real-time optical studies in the UV range of the annealing of zirconium-oxide thin films in vacuum

A multichannel spectroscopic ellipsometer is developed for real-time studies of thin films in a vacuum in the UV range. This system is mounted on a vacuum chamber to study the crystallization process of zirconium-oxide (ZrO2) thin film. The optical spectra of ZrO2 thin film are collected during the elevation of temperature. From the trend in the spectrum, we find that a threshold temperature for crystallization exists. Moreover, the crystallization occurs gradually over a certain range of temperatures between the threshold temperature and a critical temperature for full crystallization. The evolution of the dielectric function shows the development of critical peaks around 6.2 eV and 7.3 eV along with a shift of the absorption edge. To the best of our knowledge, this is the first in-situ study performed by using real-time vacuum UV spectroscopic ellipsometry, and we describe the system in detail.

Formation Behavior of Multi-Layer Oxide Films on Etched Al Foil by Vacuum Infiltration and Anodization

A vacuum infiltration method was proposed to coat uniform zirconia (ZrO2) films on etched aluminum (Al) foil. The formation behavior of the composite oxide films on aluminum (Al) foils with etch pits was different from that of flat Al foils. The multi-layer structures were formed on the ZrO2-coated Al foil after being anodized. The formation mechanism of the multi-layer films on etched Al foils was discussed. The structure and composition of each layer were investigated by scanning electron microscopy and transmission electron microscopy. The multi-layer films consisted of an inner aluminum hydrate layer, middle Al2O3-ZrO2 (Al-Zr) composite layer, and outer Al2O3 layer. Many Al3+ ions passed through the coating layer and transferred into the inner layer. A particle-like and layered structure was observed in the inner layer. The formation of multi-layer films was mainly affected by the volume expansion of the outer Al2O3 layer and the dense middle Al-Zr composite oxide film. The ZrO2 coated foils exhibited 26% higher specific capacitance than foils with only Al2O3 layer when being anodized at 600 V.

Noise and Electrical Oscillations Generation during the Investigation of the Resistive Switching in the Yttria Stabilized Zirconia Films by Conductive Atomic Force Microscopy

The effect of resistive switching in the yttria stabilized zirconia (YSZ) thin films on Si substrates has been studied by Conductive Atomic Force Microscopy (CAFM). The resistive switching of the YSZ films from the low conductive state to the highly conductive one has been found to be associated with the increasing of the noise with broad frequency spectrum related to the redistribution of the oxygen vacancies in YSZ. The electrical oscillations in oscillation loop connected in series to the CAFM probe, the sample, and the bias source related to the excitation of the oscillation loop by the noise in the probe-to-sample contact film have been observed. The effect discovered is promising for application in the memristor devices of new generation.

Residual Stress Measurement in Micro-region Using Digital Image Correlation Method

The residual stress of the zirconia film on a stainless steel substrate is measured using the digital image correlation (DIC) method. A lattice structure is milled by focused ion beam (FIB) and used as the deformation carrier. An annular groove is etched by FIB in order to release the residual stress. The DIC method is used to calculate the deformation caused by the release of residual stress and the residual stress is derived by mechanics equations. The results demonstrate that this method can be extended for micro-region residual stress measurement of other thin films on substrates.

The origin of 2.7 eV blue luminescence band in zirconium oxide

The luminescence spectra of non-stoichiometric zirconium oxide film series with different oxygen vacancies' concentrations show the blue photoluminescence band centered near a 2.7 eV peak. There is a broad band at 5.2 eV in the luminescence excitation spectrum for blue emission. The ab-initio quantum-chemical calculation gives a peak in the optical absorption at 5.1 eV for the oxygen vacancy in cubic ZrO2. It was concluded that the 2.7 eV blue luminescence excited near 5.2 eV in a zirconium oxide film is associated with the oxygen vacancy.

Zirconia films formed by plasma electrolytic oxidation: Photoluminescent and photocatalytic properties

In this paper, we have investigated photoluminescence and photocatalytic properties of zirconia films formed by plasma electrolytic oxidation (PEO) of zirconium foil in 0.1M water solution of citric acid. Zirconia films with diverse morphology and phase structure are formed varying the time of PEO process. Characterization by atomic force microscopy and X-ray diffraction shows that obtained zirconia films mostly consist of monoclinic ZrO2 phase, while corresponding roughness and crystallite size increases with PEO time. Diffuse reflectance spectroscopy has shown that zirconia films have a broad absorption band in the range from 200nm to 330nm, indicating that zirconia films could be used as a photocatalyst using ultraviolet radiation. Strong photoluminescence bands are present in spectra featuring four distinct peaks in the 300–600nm range. The peaks are centered at about 418nm, 440nm, 464nm, and 495nm. Apparent increase of photoluminescence intensity with PEO time is related to an increase of oxygen vacancy defects in zirconia films formed during the process. Also, higher concentration of oxygen vacancy defects in zirconia films result in higher photocatalytic activity.

Electrocatalytic oxidation of ethanol in acid medium: Enhancement of activity of vulcan-supported Platinum-based nanoparticles upon immobilization within nanostructured zirconia matrices

Composite electrocatalytic materials that utilize carbon (Vulcan) supported Pt or PtRu nanoparticles dispersed within thin films of zirconia ( ZrO 2) are considered here for oxidation of such a biofuel as ethanol in acid medium. The systems were characterized using electrochemical techniques as well as transmission electron microscopy. The enhancement of activity was clearly evident upon comparison of the respective voltammetric and chronoamperometric current densities recorded (at room temperature in 0.5 mol dm-3 H 2 SO 4 containing 0.5 mol dm-3 ethanol) using the Vulcan supported Pt and PtRu catalysts in the presence and absence of zirconia. In all cases, the noble metal loading was the same, 100 μg cm-2. Apparently, the existence of large population of hydroxyl groups (originating from zirconia) in the vicinity of Pt -based catalyst, in addition to possible specific interactions between zirconia and the ruthenium component of PtRu , facilitated the oxidative removal (from Pt ) of the passivating (e.g., CO ) reaction intermediates (adsorbates). By utilizing carbon supported, rather than bare or unsupported, Pt or PtRu nanoparticles (dispersed within the semiconducting zirconia), the overall charge distribution at the electrocatalytic interface was improved.