Yttria-stabilized Zirconia Phase Research Articles

Grazing-incidence synchrotron radiation diffraction studies on irradiated Ce-doped and pristine Y-stabilized ZrO2 at the Rossendorf beamline.

In this work, Ce-doped yttria-stabilized zirconia (YSZ) and pure YSZ phases were subjected to irradiation with 14 MeV Au ions. Irradiation studies were performed to simulate long-term structural and microstructural damage due to self-irradiation in YSZ phases hosting alpha-active radioactive species. It was found that both the Ce-doped YSZ and the YSZ phases had a reasonable tolerance to irradiation at high ion fluences and the bulk crystallinity was well preserved. Nevertheless, local microstrain increased in all compounds under study after irradiation, with the Ce-doped phases being less affected than pure YSZ. Doping with cerium ions increased the microstructural stability of YSZ phases through a possible reduction in the mobility of oxygen atoms, which limits the formation of structural defects. Doping of YSZ with tetravalent actinide elements is expected to have a similar effect. Thus, YSZ phases are promising for the safe long-term storage of radioactive elements. Using synchrotron radiation diffraction, measurements of the thin irradiated layers of the Ce-YSZ and YSZ samples were performed in grazing incidence (GI) mode. A corresponding module for measurements in GI mode was developed at the Rossendorf Beamline and relevant technical details for sample alignment and data collection are also presented.

Optimizing infiltration parameters of nanostructured anode electrode in solid oxide fuel cells

This study focuses on the development and optimization of nanostructured anode electrodes for solid oxide fuel cells (SOFCs) by infiltration method. Ni (nickel) catalyst in the form of a nickel nitrate solution is infiltrated into porous YSZ (yttria stabilized zirconia) backbone fabricated by tape casting. Numerous electrolyte-supported cells are fabricated to investigate the effects of several significant infiltration fabrication parameters such as catalyst loading and infiltration sintering temperature. Conventional cell with screen printed Ni-YSZ anode is also fabricated for comparison. Electrochemical performances and microstructural properties of the cells are examined and evaluated. The best peak performance of 0.398 W/cm2 at 800 °C is obtained from the cell, which is infiltrated 9 times with 2 M solution followed by firing at 800 °C. The conventional cell, on the hand, exhibits only 0.174 W/cm2 under the same testing conditions in spite of the relatively higher Ni catalyst content in the anode. Furthermore, the optimized cell produces 0.169 W/cm2 maximum power density at 700 °C. The overall results reveal that nickel catalyst infiltration is a very effective method to improve the cell performance by providing increased number of electrochemical reaction zones within the anode electrode due to nanostructured nickel catalyst formed around the main YSZ phase.

Effect of Dy2O3 doping on phase compositions, microstructures, thermophysical properties and fracture toughness of YSZ coatings

Yttria-stabilized zirconia (YSZ) coatings with different Dy2O3 doping contents were prepared via plasma spraying. The effects of phase compositions, microstructures and lattice defects on the thermal conductivity, fracture toughness and thermal shock resistance were analyzed. The result indicates that the Dy2O3 doping significantly affects thermophysical properties of YSZ coatings. The Dy2O3 doping can improve the insulation performance of the YSZ coating and the minimum thermal conductivity of the coating has reached 0.89 W/K·m. A decrease in thermal conductivity with increasing Dy2O3 doping content can be attributed to the lattice distortion, ions substitution, oxygen vacancies and reducing grain size. Meanwhile, the Dy2O3 doping causes the fracture toughness of YSZ coatings to decrease. Consequently, the Dy2O3-doped YSZ coatings exhibit weaker thermal shock resistance because the Dy2O3 doping promotes the formation of the cubic YSZ phase. The tetragonal phase in plasma-sprayed coatings is beneficial for service lifetime owing to its phase transformation and ferroelasticity-induced toughening under stress. Although the Dy2O3-doped YSZ coatings undergo more severe sintering owing to a decrease in the activation energy of grain growth caused by lattice distortion, they exhibit better phase stability than the YSZ coating under high temperatures because the Dy2O3 doping inhibits the diffusion of Y. Finally, a Dy2O3-doped ZrO2 coating composed mainly of the tetragonal ZrO2 phase was designed, which exhibited a better thermal shock resistance.

Electrical Conductivity of LSM—YSZ Oxygen Electrode for Determining Active Electrode Zone in Solid Oxide Cells

Solid oxide cells (SOCs) show high potential in applications related to sustainable society. The substantial contribution of the SOCs is their high efficiency in terms of the electric energy utilization due to the operating temperature up to 800 °C. The effect of high operation temperature is favorable in two ways. Firstly, it accelerates the kinetics of electrochemical reactions preventing the need of the use of Pt-based catalysts. Secondly, the high temperature offers favorable thermodynamic conditions decreasing the equilibrium potential for water splitting. This makes the SOCs technology a direct competitor to low-temperature technologies, such as alkaline or PEM electrolysis.The SOCs are composed of electrolyte, fuel electrode and oxygen electrode. The electrolyte allows transport of oxygen ions between the electrodes due to its high ionic conductivity. Yttria-stabilized zirconia (YSZ) represents a typical example of such a material. The oxygen electrode is where the oxygen reduction reaction or the oxygen evolution reaction takes place according to the operation mode of the SOC. Lanthanum strontium manganite (LSM) has been the state-of-the-art oxygen electrode material for almost 25 years and is considered as a pure electron conductor. Lack of ionic conductivity of the LSM leads to limitation of the overall reaction rate to the amount of triple phase boundary (TPB) where gaseous phase, electron-conducting phase and ion-conducting are in simultaneous contact. According to the literature it is optimal for the electrode material to be mixed in the 50:50 ratio with YSZ to increase the amount of the TPB. Thus, the active zone is extended further from the electrolyte surface into the volume of the electrode body. Even though the mixed electrode material exhibits great performance, information on the optimal thickness of the electrode is scarce in the literature. The electrode thickness is a crucial parameter since not all of the electrode volume is electrochemically active and represents just surplus resistance for the electric current impairing the overall electrode performance. The goal of our research is to determine of the extent of the active zone that we can estimate the optimal thickness of the LSM—YSZ electrode for various operation conditions.A macrohomogenous 1D model was developed to simulate the active electrode zone extent. Initial parametric study has shown that the extent of the active region of the electrode is influenced by many factors including the kinetics of the occurring reactions, the ionic and electronic conductivity of the respective domains and working conditions, such as temperature and operating current density. Even though the literature offers data on the conductivity of bulk the LSM and YSZ, the data of the respective conductivities in the LSM—YSZ are not applicable due to the electrode structure. The conductivity of the structure consisting of packed particles with a small contact area is limited by the contact resistance. This study targets to determine the electronic conductivity of the LSM phase and the ionic conductivity of the YSZ phase in the LSM—YSZ electrode framework.The LSM conductivity in the electrode framework was determined by resistance measurement of the casted layers of the LSM—YSZ using electrochemical impedance spectroscopy (EIS). The results show an exponential decrease of the LSM conductivity with decreasing LSM content. Furthermore, the 50:50 LSM—YSZ exhibits conductivity comparable to that of the bulk YSZ electrolyte. This result proves that the energy losses due to the electrical resistance of the LSM—YSZ electrode cannot be neglected in the terms of SOC performance.The determination of the ionic conductivity of YSZ in the electrode framework required the substitution of LSM with an inert material. The material of choice was CaSO4 due to its availability and its melting point being relatively close to that of the LSM. Similarly to the LSM, YSZ exhibited an exponential decrease of ionic conductivity with a decrease in YSZ volume fraction in the samples. Furthermore, the trend was compared to the Koh-Fortini relationship, showing that grain boundaries have a strong influence on the total conductivity of the material.The results of the experiments helped us to determine the extent of the active electrode zone leading to the estimation of optimal thickness of the LSM—YSZ oxygen electrode thickness.The authors acknowledge the financial support of the Czech Science Foundation (GACR), contract No: 19-142-44-J and by the Technology Agency of the Czech Republic under project no. TK04030143.

Phase Field Modeling of Cubic to Tetragonal Transformation in YSZ and its Effect on Ionic Conductivity Degradation and Mechanical Damages

During the high-temperature operation of solid oxide fuel cells (SOFCs), the degradations of electrolyte material yttria-stabilized zirconia (YSZ) in both ionic conductivity and mechanical strength can be caused by the cubic to tetragonal phase transformation. In this work, microelasticity phase field model is built to simulate the YSZ phase transformation considering the effects of grain boundary and solid morphology. The YSZ skeleton in real SOFC anode is reconstructed using focused ion beam-scanning electron microscopy (FIB-SEM) dual-beam technique. The ionic conductivity degradation and the mechanical damages under external mechanical loads of brittle YSZ phase in anode are investigated based on the phase field simulation results. The simulation results may provide theoretical guidelines for improving the SOFC anode during fabrication.

Preparation of epitaxial yttria-stabilized zirconia with non-quilibrium t' phase and ferroelastic domain by pulsed laser deposition

The non-equilibrium tetragonal t' phase of yttria-stabilizedzirconia (YSZ) plays a key role in improving the toughness of YSZ ceramics owing to its own ferroelastic domain toughening mechanism. Due to the disadvantages of traditional processes for preparing the YSZ t' phase, which requires high heating temperature, difficult to control defects and inability to regulate microstructure, it is not conducive to the preparation of YSZ by these methods. We report the use of substrate clamping and non-equilibrium growth process of PLD to render stable t' epitaxial YSZ films with multiple domain structure on (0001) Al2O3 substrates. Thin film structure and epitaxial relationship with substrate were subsequently analyzed by XRD, RSM, and HRTEM. It was found that the crystal orientation of the YSZ film changes as a function of oxygen pressure during deposition. When oxygenpressure is larger than 100 mtorr, YSZ films with highly oriented ferroelastic domains are obtained. Based on the symmetry relationship, we know that the film has three in-plane domain structures. The epitaxial relationship between the film and the substrate is (002) [110] YSZ // (0001) [112¯0] Al2O3.

Linear Reciprocating Wear of Yttria-Stabilized Zirconia-Based Composite Coatings Developed by Thermal Spray

Ceramic matrix composites are the preferred material for high-temperature application due to their low density, improved strength and toughness, and high-temperature capabilities. In the present study, we report the kinetics and mechanism of linear reciprocating wear of yttria-stabilized zirconia (YSZ)-based composite coatings developed by thermal spray technique. Composite coatings with different volume fractions of CoNiCrAlY and YSZ phases were subjected to linear reciprocating wear under an applied normal load of 10 N against a WC counter-body. The kinetics of wear was investigated by measuring the wear depth over time of coated components against WC surface. Adhesive wear in the 100% CoNiCrAlY coating was responsible for increased friction in the coating which changed to a three-body abrasion in the case of 100% YSZ coating. The composition coatings had a significant effect on the wear mechanism with the ceramic coatings were fractured under reciprocating load. Microcrack propagation and fracturing of ceramic splats were the dominant modes of wear in the ceramic coatings. The 100% YSZ coating showed significant wear than 100% CoNiCrAlY and 50% YSZ + 50% CoNiCrAlY coatings. The mode of wear changed with the presence of a metallic phase in the 50% YSZ + 50% CoNiCrAlY coating. The mode of wear was further studied by the detailed microstructural observation of worn track and correlating it with the wear kinetics and coefficient of friction.

Thermo-mechanical stress analyses of solid oxide fuel cell anode based on three-dimensional microstructure reconstruction

During high-temperature operation of a solid oxide fuel cell, the stresses caused by mismatch of thermal expansion coefficients between different materials and external mechanical loads may cause the rising of damage risk of nickel-yttria-stabilized zirconia anode. It is quite difficult to quantify the mechanical characteristics of a composite anode without investigating on the stress distribution in its real microstructure. However, the high operating temperature and extremely complex microstructure in micro-scale determine the high difficulty in in-situ measurement of thermo-mechanical stress distribution. In this work, the microstructures of six different anode samples, fabricated by using identical nickel oxide-yttria-stabilized zirconia powder mixture, are reconstructed in three-dimension based on the dual-beam focused-ion-beam-scanning-electron-microscopy. The three-dimensional thermo-mechanical stress distributions of different microstructures are conducted at operating temperature based on the finite element method. The effects of both thermal expansion coefficients mismatch between nickel and yttria-stabilized zirconia and external mechanical loads are analyzed. The mechanical failure probabilities of yttria-stabilized zirconia phase in different reconstructions are estimated based on the obtained stress distributions to investigate the influence of microstructure characterizations on nickel-yttria-stabilized zirconia anode strength.

Fabrication of Solid Oxide Electrolysis Single Cell Using NiO-YSZ/YSZ/LSM-YSZ via Drop-Coating Method

Solid oxide electrolysis cell (SOEC) is a highly efficient and environmentally friendly technology for future hydrogen generation. In this study, electrolyte-supported SOEC single cell was fabricated via a simple and facile drop-coating technique. Thin film electrodes of nickel oxide/yttria stabilized zirconia (NiO-YSZ) cathode and strontium-doped lanthanum manganite/ytrria-stabilized zirconia (LSM-YSZ) anode were deposited onto yttria-stabilized zirconia (YSZ) solid electrolyte substrate. Scanning electron microscopy (SEM) with energy dispersive analysis (EDS) was used to study the microstructural properties of the heat-treated samples and revealed a successful thin film deposition of porous electrodes onto the dense YSZ substrate. XRD patterns showed the desired crystal structure of the deposited electrode thin films. Distinct phases of cubic YSZ and monoclinic LSM were observed for the LSM-YSZ anode while cubic NiO and YSZ phases were observed for the deposited cathode. Electrochemical conductivity of the cell was investigated using electrochemical impedance spectroscopy analysis (EIS) which revealed a total conductivity of about 2.0 mS/cm at 700 °C.

Hot corrosion mechanism of yttria-stabilized zirconia powder in the presence of molten Na2SO4 + V2O5 salts

The hot corrosion behavior of yttria-stabilized zirconia (YSZ) powder specimens exposed to Na2SO4/V2O5 salts mixtures at high temperature was evaluated. Initial tests were carried out at 1000 °C for 10 h, the salt concentrations varied from 0.1 wt% to 1.00 wt%, and the Na2SO4/V2O5 mass ratios were between 0.20 and 0.44 following a factorial design 22. X-ray diffraction (XRD) analyses of the tested samples showed with a confidence of 95% that the mixture composed of 32 wt% Na2SO4 + 68 wt% V2O5, and 1.00 wt% salt concentration led to high destabilization of the t′-YSZ phase and formation of YVO4 products. A second set of experiments were conducted to assess the influence of temperature on the hot corrosion response of the YSZ in the range between 490 and 1100 °C. Thermogravimetric analysis (TGA) experiments and Rietveld adjustments of XRD patterns showed that the mass loss of the samples varied with testing temperature and also that the major destabilization of tetragonal phase occurred at 900 °C.

X-ray diffraction analysis of the yttria stabilized zirconia powder by mechanical alloying and sintering

In the present work, monoclinic zirconia was mechanically alloyed with yttria (6–14 mol%) via ball milling at the different ball-to-powder mass ratios (BPMRs) for 3–24 h, and then, the mixed powders were sintered at 1100 °C and 1500 °C. Line profile analysis of the X-ray diffraction (XRD) patterns, using the Alexander-Klug, Adam-Cox, Rietveld, and Scherrer methods, was systematically used to investigate the effects of the milling time, BPMRs, sintering temperature, sintering time and zirconia-to-yttria ratio. The experimental results indicate that the yttria-stabilized zirconia (YSZ) appears in the mixed powder after a milling time longer than 8 h. In addition, the ZrO2 content will decrease with the milling time or amount of BPMRs. The XRD patterns demonstrate that the intensity of the YSZ diffraction peaks was greatly improved after sintering. However, even if sintering at 1100 °C for 10 h, m-ZrO2 still remained in the mixed powder. When the temperature rose to 1500 °C, only the cubic phase of YSZ (c-YSZ) was found in the zirconia-14 mol% yttria powder. Based on the above results, combined with other related research, the possible mechanism of the phase transformation in the ball milling and sintering process is discussed in this paper.

YSZ nanoparticles and thin films prepared in a single crystallization step at low temperature

Yttria Stabilized Zirconia (YSZ) are among the most versatile materials of the modern age, but their preparation requires high temperatures and several crystallization steps. Here we report how YSZ nanoparticulated powders and thin films have been obtained in a single crystallization step at lower temperatures than others reported before. Solid precursors with different molar ratios between ammonium nitrate and Zr-Y-citrate were studied to approach an optimal fuel/oxidizer ratio that guarantees a complete autocombustion of the precursor, so that cubic 10.5% mol YSZ nanoparticles are synthetized in one step at 400 °C. A solid precursor optimized as described before was employed for the fabrication of dense and granular YSZ thin films combining, for the first time, the Ultrasonic Spray Pyrolysis with an autocombustion reaction. The samples were structurally, thermally, morphologically, optically and electrically characterized. The cubic 10.5% mol YSZ nanoparticles exhibit an ionic conductivity close to 0.2 S cm−1 at 620 °C. The cubic 12.5% mol YSZ phase predominates in the micrometric particles agglomerates observed in the granular film, where the impedance response was very resistive. Nanoparticles of 7.5% mol YSZ with a two-phase mixture (tetragonal/cubic) predominate in the dense film. In this film refractive index as high as 1.98 and conductivity around 0.1 S cm−1 at 600 °C were measured. These results are promissory for applications at low temperatures.

Confined Transformation of UiO‐66 Nanocrystals to Yttria‐Stabilized Zirconia with Hierarchical Pore Structures for Catalytic Applications

AbstractSolid acids as a substitution for hazardous liquid acids (e.g., HF and H2SO4) can promote many important reactions in the industry, such as carbon cracking, to proceed in a more sustainable way. Starting from a zirconium‐based metal‐organic framework (UiO‐66 nanocrystals), herein a transformative method is reported to prepare micro/mesoporous yttria‐stabilized zirconia (YSZ) encapsulated inside a mesoporous silica shell. It is then further demonstrated that the resultant reactor‐like catalysts can be used for a wide range of catalytic reactions. The acidity of the YSZ phase is found with rich accessible Lewis acid and Brønsted acid sites and they display superior performances for esterification (acetic acid and ethanol) and Friedel‐Crafts alkylation (benzylation of toluene). After being loaded with different noble metals, furthermore, hydrogenation of CO2 and a one‐pot cascade reaction (nitrobenzene and benzaldehyde to N‐benzylaniline) are used as model reactions to prove the versatility and stability of catalysts. Based on the findings of this work, it is believed that this class of reactor‐like catalysts can meet future challenges in the development of new catalyst technology for greener heterogeneous catalysis.

Thermal Stability of YSZ Coatings Deposited by Plasma Spray–Physical Vapor Deposition

The plasma spray–physical vapor deposition (PS–PVD) process has received considerable attention due to its non-line of sight deposition ability, high deposition rates, and cost efficiency. Compared with electron beam–physical vapor deposition (EB–PVD), PS–PVD can also prepare thermal barrier coatings (TBCs) with columnar microstructures. In this paper, yttria-stabilized zirconia (YSZ) coatings were fabricated by PS–PVD. Results showed that the as-deposited coating presented a typical columnar structure and was mainly composed of metastable tetragonal (t′-ZrO2) phase. With thermal exposure, the initial t′ phase of YSZ evolved gradually into monoclinic (m-ZrO2) phase. Significant increase in hardness (H) and the Young’s modulus (E) of the coating was attributed to the sintering effect of the coating during the thermal exposure, dependent on exposure temperature and time. However, the values of H and E decreased in the coatings thermally treated at 1300–1500 °C for 24 h, which is mainly affected by the formation of m-ZrO2 phase.

Effects of YSZ powder properties on its corrosion behaviour for solid oxide membrane (SOM) electrolysis process

The solid oxide membrane (SOM) process is an environmentally friendly and innovative technology that can produce valuable metals directly from their oxides. In the SOM process, a yttria-stabilized zirconia (YSZ) tube is normally immersed the molten salt containing dissolved metal oxides and oxygen anions that move to the SOM tube where they are reduced without any emission. However, the YSZ phase transition and yttrium dissolution by the reaction with the flux reduce the SOM stability and lifetime. Here, we investigated the effect of powder characteristics on YSZ stability in the SOM electrolysis environment. Thus, powder with good formability such as high flowability and tap/untap density showed a 2% decrease in electrical conductivity, but a 17% decrease in low formability powders. The cause of the degradation is the penetration of salt ions into the lattice and the elution of yttrium ions, which results in a phase transition.

Evaluation of electrochemical performance of solid-oxide fuel cell anode with pillar-based electrolyte structures

Among the gas, ion, and electron diffusion processes in solid-oxide fuel cell (SOFC) electrodes, it is generally known that ionic conduction has the most impact on their electrochemical performance. Therefore, enhancement of the effective ionic conductivity of electrodes is a useful approach to reduce the overpotential. Yttria-stabilized zirconia (YSZ) pillars can be effective solutions to enhance the effective ionic conductivity of SOFC anodes. In this study, the influence of YSZ pillar structures on the electrochemical performance of SOFC anodes was evaluated by numerical simulation and experiments. First, to reveal the electrochemical reaction kinetics of anodes with pillar structures, a three-dimensional electrochemical simulation was conducted by the lattice Boltzmann method. The microstructure without pillars obtained by a focused ion beam scanning electron microscopy (FIB-SEM) measurement was used as the reference structure. Then, the original structure was replaced with YSZ phase to obtain virtual microstructures with YSZ pillars. With YSZ pillars, predicted area specific resistance became smaller than that of the reference structure, in spite of decrease in percolated TPB density. The electrochemical potential distribution of oxide ion and charge-transfer currents clearly show increase in the effective ionic conductivity. Relationships between overpotential and pillar geometries were parametrically discussed. Then, electrochemical performance of Ni-YSZ anode with the YSZ pillar structure formed by modifying the YSZ electrolyte surface was evaluated. By sputtering Ni-YSZ on pillar structures, stable electrochemical performance was obtained.

Highly efficient up-conversion green emission in Ho/Yb co-doped yttria-stabilized zirconia single crystals

In the development of materials with valuable luminescence properties, we have used the optical floating zone method to prepare single crystals in the cubic phase of yttria-stabilized zirconia (YSZ) doped with 0.75 mol% Ho2O3 and various concentrations of Yb2O3. The influence of Yb3+ contents was determined for absorption and photoluminescence spectra, and fluorescence decay curves at room temperature. The absorption spectra consisted of several peaks that could be assigned to various transitions involving Yb3+ and Ho3+ ions, and oscillator strength parameters Ωt (t = 2, 4, 6) were determined using the Judd-Ofelt theory, along with the transition probability, lifetime, and branching ratio from the absorption and emission spectra of the crystal of YSZ co-doped with 0.75 mol% Ho2O3 and 1.5 mol% Yb2O3. The Ω2 value of ~14 × 10–20 cm2 indicates that the bonding around Ho3+ involves lower symmetry and higher covalency than in several other hosts, and the value of the ratio Ω4/Ω6 of 1.93 shows that this sample is a good candidate material for high quality laser output. Up-conversion emission spectra showed that Yb3+ doping significantly increased the emission intensity of 0.75 mol% Ho2O3 doped YSZ at green (557 nm), red (670 nm) and NIR (758 nm) wavelengths when excited by a 980 nm laser, and reached a maximum for 1.5 mol% Yb2O3. The emission at 557 nm was much sharper than that reported for nanocrystals of similar composition, where the maximum intensity was observed at 540 nm. Down-conversion PL spectra showed two prominent emission peaks at 1040 nm and 1213 nm, and the fluorescence decay curves indicate that energy transfer between Yb3+ and Ho3+ influenced the lifetime of the excited state of Ho3+ which varied with Yb2O3 concentration. Overall these results indicate that these Yb/Ho co-doped YSZ crystals have considerable potential for laser and luminescence applications.

Preparation and characterization of yttria stabilized zirconia (YSZ) films deposited by dip-coating on LSM-YSZ substrate with different proportions

ABSTRACT In this work, sol-gel/dip-coating process for obtaining yttria stabilized zirconia (YSZ, ZrO2–8% Y2O3) films deposited onto LSM-YSZ (lanthanum strontium manganite (LSM, La0.7Sr0.3MnO3) mixed with YSZ) with different proportions (20/80, 50/50, 80/20) was investigated. The films were deposited on substrate varying the number of layers deposited. LSM powders were obtained by the combustion method using metal nitrates and urea and YSZ was commercial. LSM-YSZ composite powders were obtained by the solid state method, through ball-milling of a mixture of LSM-YSZ (mass ratio) powder for 4 h with 500 rpm using ZrO2 balls as milling media. For LSM-YSZ substrate a study of sintering temperature was performed, where the optimum sintering temperature for each LSM-YSZ studied proportion was obtained. According to our results, it was found that 1100 oC is the optimum sintering temperature for 20/80, 950 oC is the optimum sintering temperature for 50/50 and 900 oC is the optimum sintering temperature for 80/20 because of the good phase formation. The films were characterized by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The films showed LSM, YSZ, SrZrO3 and La2O3 phases. Crack-free, homogeneous and well adhered films were obtained with a thickness between 3 and 38 µm. In this work, YSZ films with appropriate thickness were obtained for application as SOFC electrolyte.

Effects of Thickness on the Electrical Conductivity of Sputtered YSZ Film with Nanocrystalline Columnar Microstructure

In order to investigate the effect of the thickness on the electrical conductivity of yttria-stabilized zirconia (YSZ) film, the nanocrystalline columnar-structured YSZ film with thickness of 0.67-2.52 μm was prepared by magnetron sputtering through controlling the deposition time. All the sputtered films with different thicknesses consist of the main phase of cubic YSZ as well as a small amount of monoclinic YSZ. The thicker films exhibit a typical columnar grain structure based on the fractured cross-sectional SEM observations. The average diameters of columnar grains increase from about 40 nm to 100 nm with the film thickness from 0.67 μm to 2.52 μm according to TEM analysis. The thinnest YSZ film with 0.67 μm thickness shows the highest apparent electrical conductivity in the four films in 400–800 °C due to the contribution from the highly conductive film/substrate interfacial region. On the other hand, the real electrical conductivities of YSZ films increase with film thickness from 0.67 μm to 2.52 μm after eliminating the contribution of the film/substrate interface. The increasing film thickness leads to the grain growth as well as the decrement in the volumetric fraction of the resistive columnar grain boundary and a consequent higher real electrical conductivity.

Reduced activation energy of nano size phase formation in yttria stabilized zirconia film obtained by RF magnetron sputtering: Preliminary results

Yttria stabilized zirconia (YSZ) is a well-known ceramic material used for many various applications including a buffer layer for growth of functional oxide thin films on Si in semiconducting silicon chip technology. In the present work, YSZ thin film deposition on Si (100) substrate using magnetron sputtering system at room temperature is considered. The films were characterized by several methods: X-ray Photoelectron Spectroscopy (XPS), High Resolution Scanning Electron Microscopy (HRSEM) and X-ray diffraction (XRD). They were used in order to get information regarding the composition and the uniformity of the samples, determine their crystal structure and measure the grain size and the thin films thicknesses, respectively. In addition, the kinetics of the YSZ phase growth was investigated. Several samples were heat treated for one hour in air at various temperatures in the 500-650 °C temperature range, which made it possible to estimate the apparent activation energy of the process. The thin film characterization by XPS showed uniformity in composition through the entire depth of the film. This composition complies with the composition of 8YSZ known in the literature. This was expected since the sputtering target was 8YSZ. A decrease in film thickness and of the crystallization process was observed by XRD and HRSEM. The growth of the YSZ phase and its formation kinetics showed very low activation energy of ∼ 10.6 – 13.5 kJ/mol.