YSZ Single Crystal Substrates Research Articles

High surface proton conduction of a-axis oriented CeO2−δ thin film on (200) YSZ substrate

Abstract We have prepared a-axis oriented CeO2−δ thin films prepared on yttrium-stabilized zirconium (200) single crystal substrates by RF magnetron sputtering using a ceramic target. The amount of oxygen vacancies in the CeO2−δ thin films was quantitatively evaluated by X-ray absorption spectroscopy and defect chemical analysis. In terms of its electronic structure, the O 1s photoemission spectrum of the wet-annealed film shows an O–H bond peak, which suggests proton conduction. The a-axis oriented CeO2−δ thin film annealed at 600 °C in a wet atmosphere exhibit high proton conductivity of more than 101 Scm−1K at medium temperature range from 300 °C to 550 °C by thermal activation process and surface proton conductivity of σT = ∼7.0 × 10−1 Scm−1K by Grotthuss mechanism below 50 °C. The enhancements of proton conductivities are considered to be due to large amount of oxygen vacancies of ∼3.3% at the surface of wet-annealed CeO2−δ thin film. These results indicate that the wet-annealed a-axis oriented CeO2−δ thin films can be applied as an electrolyte for solid oxide fuel cell operating at medium temperature range or electric double layer transistor operating below 50 °C.

Infiltration of La2NiO4+ᵟ-Type Electrodes with Nano-Oxide Catalyst to Modify Electrochemical Properties and Stability Using Biomolecular Surface Engineering

Solid oxide electrolysis cells (SOECs) have increased in importance in recent years due to their potential to cleanly and efficiently separate hydrogen and oxygen, or to instigate other chemical conversion reactions. SOECs require a combination of both high start performance and low long-term degradation for optimal electrodes. Additionally, Cr-poisoning from metal interconnect components threatens long-term degradation due to the ambient humidity of the electrolysis process. The most promising candidate for the oxygen electrode was (La,Sr)(Co,Fe)O3±δ (LSCF) due to its excellent electrical and catalytic properties, but it is challenged by a SrZrO3 phase, Cr-poisoning, and decreased oxygen ionic conductivity under high current loads due to its reliance on oxygen site vacancy (VÖ ) concentration. This drives interest into the Ruddlesden-Popper (R-P) phase, which has the general K2NiF4-type structure. Of these, La2NiO4+δ (LNO) is interesting, as its ionic conductivity mechanism is interstitial oxygen (Oï ) and it has no apparent reaction under Cr-poisoning. A challenge, however, is LNOs relatively low surface oxygen transport. As such, this project’s focus is on the surface engineering of a heterostructured oxygen electrode with LNO as a backbone and an infiltrated LaCoO3-δ (LCO)-based perovskite layer.In this work, the surface engineering of the LNO surface was completed by utilizing a novel wet biomolecular infiltration technique to ensure homogenous nano-particle coatings. The process involves a primary deposition of a catechol surfactant throughout the LNO electrode, and then a secondary deposition of the nano-catalyst solution. The catechol molecule that is deposited in the first step enables the adhesion of the nano-oxide, helping to chelate the complex oxide and assisting in the formation of the compound. No further deposition steps are needed, increasing the overall efficiency and the controllability of the microstructure, and allowing for the formation of the multicomponent nanomaterial at temperatures <800 °C. This has the additional benefit of minimalizing the densification and/or reaction of the nanomaterial with the electrode backbone (if not desired).The initial objective of the work was to characterize the nano-catalyst deposition process on the electrode surface, and define characteristics such as surface roughness, homogeneity, and particle size as function of deposition parameters and surfactant type/concentration. This work was completed initially on an electrode surrogate, YSZ single-crystal substrates. First, a deposition study was run on single-crystal, polished YSZ substrates, chosen for their flatness which simplifies the microstructural characterization through atomic force microscopy (AFM). AFM images from this deposition were processed to gather data on sample surface roughness, and both particle homogeneity and volumetric data, indicating which variables were most important to adjust. An example of these images can be seen in Figure 1 below, an AFM graph of the topography of deposited nano-particles. After defining the deposition process on flat YSZ substrates, the deposition methods were transferred to LNO symmetrical cells and full SOECs. Half and full cells were screen-printed on a YSZ electrolyte, with a GDC barrier layer, a 50-50 wt % LNO/GDC active layer, and an LNO current collector layer. The electrochemical impedance spectroscopy (EIS) tests were completed on infiltrated and non-infiltrated cells at different loading levels (defined by the impregnation variables) to evaluate the effectiveness of the nano-oxide surface engineering on the desired characteristics of surface oxygen transport and charge transfer reactions. The cells were tested in air and various steam concentrations up to 800 °C. Acknowledgments: This research was funded by the US Department of Energy, Project DE-FE0032116. We would also like to thank the WVU Shared Research Facilities for their support, specifically Dr. Qiang Wang, Dr. Marcela Redigolo, and Mr. Harley Hart for their help. Figure 1

Ca segregation at Au–YSZ interfaces

Au thin films deposited on (111) YSZ single-crystal substrates were dewetted and equilibrated in a low oxygen partial pressure (10−20 atm) at 950 °C. Electron backscattered diffraction of 150 equilibrated Au particles shows that there is no preferred low-index orientation relationship (in-plane orientation relationship) but rather a strong preferred orientation of {111} Au || {111} YSZ. This result is associated with identical interface energies (1.75 ± 0.02 J/m2) measured using Winterbottom analysis from three equilibrated Au particles with different orientation relationships with the YSZ substrate. Energy dispersive spectroscopy in a scanning transmission electron microscope of the interfaces showed a Ca excess of Γ = 1.65 ± 0.20 atoms/nm2 (detection limit of 0.12 atoms/nm2). It is believed that Ca segregation reduces the interface energy of the system, resulting in a more isotropic orientation distribution instead of a low-index orientation relationship normally seen between fcc metals and YSZ.

Elucidating the Origin of Oxide Ion Blocking Effect at GDC/Srzr(Y)O3/YSZ Heterointerfaces

Solid oxide fuel cells (SOFCs) have attracted significant attention over recent years due to their promising use as source of clean and efficient power generation. Towards the goal of enhancing the efficiency of these devices, it is important to eludicate the mechanisms governing fundamental electrochemical processes, specifically incorporation and transport of oxygen species across heterostructures. Degradation of cell performance has been attributed to the formation of SrZrO3 (SZ), especially along the GDC/YSZ interface, resulting from cation interdiffusion across LSCF/GDC/YSZ heterostructures. In this study, using a combination of isotope oxygen tracer and secondary ion mass spectroscopy (SIMS) depth profiling, we examined oxide ion transport in dense SZ and Y-doped SrZrO3 (SZY) thin films in conjunction with other oxide materials in a multilayered heterostructure, viz., GDC/SZ(Y)/YSZ. The GDC/SZ(Y) multilayers were prepared on (100) YSZ single crystal substrates using pulsed laser deposition; X-ray diffraction results confirmed that the SZ and SZY films were highly oriented along (h00). SIMS depth profile measurements after isotope exchange revealed that ionic transport is drastically inhibited at the SZ(Y)/YSZ interface, indicating the existence of an oxide ion barrier which blocks ionic flow. A similar behavior was also observed at the GDC/SZ interface; however, this was not observed for GDC/SZY. To elucidate the mechanism for the oxide ion blocking effect, we performed detailed microstructural analyses of the interfaces using transmission electron microscopy (TEM) and spatially resolved electron energy loss spectroscopy (EELS) technique. TEM results showed that the GDC/SZ(Y) and SZ(Y)/YSZ interfaces are atomically sharp and devoid of any secondary phases. The SZ film also appears to contain a high density of microstructural defects such as stacking faults which extend across its thickness. Furthermore, evident changes in the O K-edge EELS spectra measured across the heterostructures suggest the possible existence of oxygen disorder in the YSZ region adjacent to the SZ(Y)/YSZ interface. This may indicate a possible link between oxygen disorder, which can effectively break the oxygen diffusion pathways, and blocking of oxide ion transport across the SZ(Y)/YSZ interface.

In situ X-ray Studies of (La,Sr)MnO3_δ, (La,Sr)CoO3_δ, and La0.6Sr0.4Co0.2Fe0.8O3-δ Thin Film SOFC Cathodes Grown by Pulse Laser Deposition

ABSTRACTWe will briefly review in situ synchrotron x-ray investigation of model thin film cathode systems for solid oxide fuel cells. The film cathodes examined in this study are (La,Sr)MnO3_δ (LSM), (La,Sr)CoO3_δ (LSC), and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) thin films epitaxially grown on YSZ single crystal substrates by the pulse laser deposition technique. We find in all cases that Sr is enriched or segregated to the surface of the film cathodes. We concluded that the Sr enrichments or segregations are mainly the results of annealing because they do not depend on whether the cathodes are electrochemically biased or not during annealing. However, at least in the case of LSCF, we find that B-site Co segregates rather uniformly to the surface and the segregation responds sensitively and reversibly to the electrochemical bias.

Effect of La 2Zr 2O 7-buffered YSZ substrate on YBa 2Cu 3O y thin films by chemical solution deposition

Epitaxial YBa 2Cu 3O y (YBCO) thin films have been fabricated by chemical solution deposition (CSD) on La 2Zr 2O 7-buffered YSZ single crystal substrate, where the buffer layer has three kinds of morphology – flat surface, rough surface and pore surface. The effect of LZO buffer layer’s roughness on the YBCO films was evaluated by X-ray diffraction, scanning electron microscopy and temperature-dependent resistivity measurements. The flat surface of LZO layer is beneficial to highly epitaxial YBCO films and high critical current density.

Texture analysis of RF-sputtered CeO2 buffer layers and superconducting MOD-YBCO films

CeO2 buffer layers were deposited on YSZ single-crystal substrates using an RF-sputtering method. The development of crystalline textures of sputtered CeO2 films at different sputtering pressure and their effects on YBCO films, deposited by Metal Organic Deposition (MOD), were investigated. Both CeO2 and subsequent YBCO films grew well epitaxially. The relative XRD peak intensities of CeO2 (200) to substrate YSZ (200) increased with deposition pressure in the range of 3–5mTorr and were inversely proportional to the θ–2θ scan FWHM values of CeO2 (200). Also, the reaction layers of BaCeO3 were thicker in the samples with lower CeO2 (200) intensities and poor out-of-plane alignment when CeO2 were deposited at the lower pressure of 3.3mTorr. It is noted, however, that the superconducting layer grew well epitaxially on these BaCeO3 layers, possibly due to the epitaxial relation between CeO2 and YBCO. The superconducting critical currents of MOD-YBCO films showed an increasing tendency as both the Δ2θ (CeO2) and BaCeO3 peak intensities decreased.

Fabrication and properties of superconducting single crystal cross-(micro)whiskers junction

Superconducting single crystal Bi-2212 (micro)whiskers have been fabricated by annealing a glass Bi 2Sr 2Ca 2Cu 3O x precursor. The T c and T zero of ∼20 mm long and 10–70 μm wide single crystal whiskers were found to be 85 K and 82 K, respectively. The critical current density J ctransport of the whiskers was calculated to be 1313 A cm −2 at 0 T and 10 K. Then, a couple of whiskers were placed cross-wise on the YSZ single crystal substrate and heat treated to form micro-scale junction. The I– V characteristics of the micro-junction at 10, 30 and 60 K were found to show a multiple branch structure and that confirms to a model based on intrinsic Josephson junction.

Chemical solution deposition preparation of highly (2 0 0)-oriented La 0.8Na 0.2MnO 3 films on YSZ and LaAlO 3 substrates

La 0.8Na 0.2MnO 3 films were successfully fabricated via the chemical solution deposition (CSD) method on LaAlO 3 and YSZ single crystal substrates. The results showed that the two samples behaved like epitaxial films. It was suggested that it was possible to fabricate highly (h 0 0)-oriented colossal magnetoresistance films on YSZ substrates using CSD.

CeO/sub 2/ buffer layers deposited by pulsed laser deposition for TFA-MOD YBa/sub 2/Cu/sub 3/O/sub 7-X/ superconducting tape

A CeO/sub 2/ buffer layer was deposited by the pulsed laser deposition (PLD) method on a YSZ single crystal substrate and an IBAD-Gd/sub 2/Zr/sub 2/O/sub 7/ substrate. It was investigated in terms of the effect of the CeO/sub 2/ layer thickness for YBa/sub 2/Cu/sub 3/O/sub 7-X/ (YBCO) coated conductors by the metalorganic deposition method using trifluoroacetates (TFA-MOD). The grain alignment, delta phi, and surface roughness, R/sub a/, of CeO/sub 2/ layers were improved with increasing the thickness for both kinds of substrates of a YSZ single crystal and an IBAD-Gd/sub 2/Zr/sub 2/O/sub 7/ substrate. Especially the improvement of the qualities of the CeO/sub 2/ layer on the IBAD substrate was remarkable. The initial value of delta phi was 12 degree at the surface of the IBAD-Gd/sub 2/Zr/sub 2/O/sub 7/ layer without a CeO/sub 2/ layer while it decreased to 4 degree after 600 nm thick CeO/sub 2/ layer deposition by PLD. Consequently, the J/sub c/ value of the YBCO on the CeO2 buffered IBAD-Gd/sub 2/Zr/sub 2/O/sub 7/ metallic substrate exhibited the value as high as 2.9 MA/cm/sup 2/ at 77 K and 0 T. This result implies that a high rate deposition by PLD could be used for further texture evolution even after thin film IBAD deposition which could result in shortening of the overall production time for the buffer layers deposition.

Effect of substrate on magneto-transport properties of polycrystalline manganite films

Polycrystalline films of La0.7Ca0.2Ba0.1MnO3 (LCBMO) were deposited on LaAlO3, SrTiO3 (STO), Al2O3 and YSZ single crystal substrates by spray pyrolysis technique employing an ultrasonic nebulizer. Deposition and annealing conditions for all four films were kept identical. All films have been found to be single phase and have orthorhombic unit cells with only slightly different lattice parameters. The magneto-transport properties (magnetoresistance (MR), TC and TIM) of these polycrystalline LCBMO films are found to depend strongly on the substrate. The lattice mismatch between the film and substrate induces strain of various degrees. The strain is believed to get relaxed and accommodated. This produces disorders dominantly through the increase in the grain boundary density and hence decrease in grain size. The largest strain leads to the creation of highest degree of disorder. The observed MR for the case of YSZ/LCBMO is found to be significantly higher than other case of STO/LCBMO. As for example, for YSZ/LCBMO where the lattice mismatch is −24.280%, MR is ∼7%, on the other hand for STO/LCBMO where the lattice mismatch is −0.333%, MR is ∼2.3%. The TC and TIM for the film with higher disorder (YSZ/LCBMO) is significantly reduced as compared to the case of the film having lower disorder (STO/LCBMO). The TC for YSZ/LCBMO (higher disorder) is 243 K and for STO/LCBMO (lower disorder), it is 285 K.

Growth characteristics of HgBa 2CaCu 2O 6 superconducting films on CeO 2-buffered YSZ single crystals: an assessment for coated conductors

Superconducting HgBa 2CaCu 2O 6 (Hg-1212) films have been fabricated on CeO 2-buffered YSZ single-crystal substrates using a two-step cation-exchange process. X-ray diffraction analyses show that the Hg-1212 films are highly crystalline and grow epitaxially on these CeO 2/YSZ substrates. Although the superconducting transition temperatures ( T c) of these films are approximately 122 K, the critical current densities ( J c) fall far below the expected values. The reason for these low- J c values is explained by the observations of a cracked surface morphology in the superconducting layers. The likely mechanism for formation of the cracks and implications for the development of Hg-based coated conductors are discussed.

Progress towards a low-cost coated conductor technology

Progress in the development of an economically and technically viable YBCO coated conductor technology for HTS wire using deformation-textured buffered substrates and solution-deposited superconductor layers is reported. Biaxially textured Ni substrates have been fabricated using a deformation texturing process. Epitaxial oxide buffer layers have been deposited by a combination of e-beam deposition and magnetron sputtering. Epitaxial YBCO films have been grown using a trifluoroacetate solution precursor. The resulting composite conductors have critical current densities approaching 2 MA/cm 2 at 77K in self-field. Critical current densities of 4.5 MA/cm 2 have been also obtained on CeO 2 buffered YSZ single crystal substrates, demonstrating performance parity with vacuum deposited YBCO films.

Epitaxial superconducting thin films Tl 0.78Bi 0.22Sr 1.6Ba 0.4Ca 2O 9−δ on (001) YSZ synthesized by laser ablation and post-annealing in pure argon

Epitaxial superconducting thin films of Tl 0.78Bi 0.22Sr 1.6Ba 0.4Ca 2Cu 3O 9−δ ((Tl,Bi)-1223) on (001) YSZ single crystal substrate have been successfully synthesized by laser ablation and post-annealing in a tube furnace with flowing pure argon through the tube all the time during annealing. X-ray diffraction (XRD) θ–2θ spectra showed that the films are c-axis aligned 1223 phase with a small amount of intergrown 1212 phase, while XRD φ-scans revealed that the films are also a- and b-axes aligned, with an epitaxy of the &.lang;100&.rang; of (Ti,Bi)-1223 film on the &.lang;110&.rang; of the YSZ substrate. Four-terminal electrical transport measurements showed that the zero-resistance transition temperature ( T c) was 108.5 K, and the critical current density ( J c) at 77 K and zero field was 1.1 × 10 6 A/cm 2, both for the entire film width and for a patterned bridge. The magnetic field dependent transport J c suggest that (Tl,Bi)-1223 films on (001) YSZ have better flux-pinning properties than high- J c (Tl,Bi)-1223 films on (001) LaAlO 3.

Preparation of high-Tc superconducting thin films of Tl-Ca-Ba-Cu-O by the chemical spray pyrolysis technique

Thin films of the Tl-Ca-Ba-Cu-O system have been prepared on MgO and YSZ single-crystal substrates by a simple chemical process (the spray pyrolysis technique). Since Tl is toxic, the Tl-Ca-Ba-Cu-O films were prepared by a two step process. Firstly, precursor (Ca-Ba-Cu-O) films were prepared followed by diffusion of Tl derived by vaporizing Tl2O3 in a closed system under oxygen flow. A new feature found in the present investigation is that the Tc (R=0) of the Tl-Ca-Ba-Cu-O films has been found to depend upon the microstructural characteristics of the precursor films which can be varied by annealing these films. The Tc (R=0) of the Tl-Ca-Ba-Cu-O HTSCs films prepared from the annealed precursor films has been found to be higher than in the films prepared from the as-deposited precursor films. As, for example, in the case of a film on a MgO substrate, the Tc (R=0) has been enhanced from approximately 90 K to approximately 98 K. The highest Tc obtained by the authors for the films synthesized from the annealed precursor films on YSZ substrates corresponds to approximately 103 K. The XRD reveals the biphasic (2223/2122) nature of the films. The microstructural characteristics of the films as monitored by SEM reveals the partially oriented nature of the Tl-Ca-Ba-Cu-O film.

Mechanisms of Plasma Oxidation of Si

AbstractFundamental aspects of the interaction between non equilibrium, low pressure oxygen plasma and Si (silicides) are described. The kinetics of oxide growth in oxygen atmosphere, in plasma at low pressure (p&lt;∼ 1 Torr) and low temperature (T &lt; 1 800°C) regimes are reviewed and the Cabrera-Mott mechanism is postulated i.e. the oxidation process is controlled by ion injection at the plasma/oxide interface. The mechanism of electron injection and conduction during plasma anodization is reviewed and discussed in the frame of theory of high current injection in MIS structure. Enhancement of oxide growth rate due to the irradiation (laser), bombardment by electrons or ions is reviewed and compared to the plasma oxidation. Spectacular enhancement of the anodization rate of Si covered by a thin deposited layer of zirconia or hafnia oxide is analyzed. The anodization rate of Si deposit through ∼’ 0.5 mm YSZ single crystal substrate is evoked as an example of potentiality of plasma anodization process. The mechanism of movement of oxygen ions and of cations deduced from 160/180 experiments is discussed. A few examples of applications of Si plasma oxidation processes are presented.