Yttria-stabilized Zirconia Substrates Research Articles

Chemical expansion of CeO2−δ and Ce0.8Zr0.2O2−δ thin films determined by laser Doppler vibrometry at high temperatures and different oxygen partial pressures

The chemical expansion of ceria (CeO2−δ) and ceria-zirconia (Ce0.8Zr0.2O2−δ, CZO80) thin films is investigated by high-temperature laser Doppler vibrometry (LDV) at temperatures from 600 to 950 °C. The films are deposited on single-crystalline 8 mol-% yttria-stabilized zirconia substrates, which act as pumping cells to adjust oxygen non-stoichiometry in the thin films. Oxygen deficiency causes film expansion, leading to mechanical strain that bends the sample. The total displacement, i.e., the sum of bending and film-thickness change, is determined contact-less by LDV. A differential laser Doppler vibrometer (D-LDV) is realized to enable measurements on a very long time scale, which is necessary due to the long equilibrium times of the ceramic films. These displacements are compared to those acquired with a commercial single-point laser Doppler vibrometer (SP-LDV) for motions above 1 Hz. Here, both devices yield similar results. CZO80 films are found to bend a substrate much more than ceria films under similar experimental conditions. A model describing the displacement of the sample is derived from the Stoney model and applied to calculate deflections using literature data. The displacements at the center of the CZO80 sample measured with the SP-LDV increase from 0.18 nm at 10 Hz and 600 °C to 32.7 nm at 0.1 Hz and 800 °C. For ceria, the displacements range from 1.6 nm (10 Hz, 800 °C) to 79.4 nm (0.1 Hz, 900 °C). The D-LDV enables the detection of quasi-static displacements at very low frequencies. The ceria sample exhibits 218 nm at 0.001 Hz and 800 °C.

Electrophoretic deposition of YSZ layers on pyrolytic graphite and a porous anode substrate based on NiO-YSZ

Solid oxide fuel cells are promising hydrogen energy devices. The goal of this research was to create ceramic layers for SOFCs based on yttria-stabilized zirconia (YSZ) and to investigate their parameters. YSZ ceramic layers with a thickness of 5.14 μm on a porous NiO–YSZ substrate and 7 μm on pyrolytic graphite were obtained by electrophoretic deposition. X-ray diffraction and electron microscopy were used to determine the composition, structure, and morphological features of ceramic layers. The effects of the substrate's nature, the degree of dispersion of the initial YSZ powder, and the heat treatment conditions on the properties of the ceramic layer YSZ were considered.

Preparation and characterization of YMnO3 thin films by metal–organic decomposition

Hexagonal rare-earth manganese oxide YMnO3 thin films were prepared on yttria-stabilized zirconia (111) substrates by metal organic decomposition method. The crystallinity and morphology of YMnO3 thin films crystallized at various temperatures were examined by X-ray diffraction and atomic force microscopy measurements, respectively. Single phase YMnO3 was obtained for the sample prepared by annealing temperatures of 950 °C. AFM analysis revealed that a smooth surface with a roughness of 0.15 nm was achieved for YMnO3 thin film annealed at 950 °C and 1000 °C, while three-dimensional growth for other samples prepared at 750–900 °C, 1050 °C, and 1100 °C. A narrow band at 1.6 eV and a broad band at 5 eV due to electronic transitions in the manganese and oxygen bands were observed in an absorption spectrum.

MOCVD growth and band offsets of κ-phase Ga2O3 on c-plane sapphire, GaN- and AlN-on-sapphire, and (100) YSZ substrates

Epitaxial growth of κ-phase Ga2O3 thin films is investigated on c-plane sapphire, GaN- and AlN-on-sapphire, and (100) oriented yttria stabilized zirconia (YSZ) substrates via metalorganic chemical vapor deposition. The structural and surface morphological properties are investigated by comprehensive material characterization. Phase pure κ-Ga2O3 films are successfully grown on GaN-, AlN-on-sapphire, and YSZ substrates through a systematical tuning of growth parameters including the precursor molar flow rates, chamber pressure, and growth temperature, whereas the growth on c-sapphire substrates leads to a mixture of β- and κ-polymorphs of Ga2O3 under the investigated growth conditions. The influence of the crystalline structure, surface morphology, and roughness of κ-Ga2O3 films grown on different substrates are investigated as a function of precursor flow rate. High-resolution scanning transmission electron microscopy imaging of κ-Ga2O3 films reveals abrupt interfaces between the epitaxial film and the sapphire, GaN, and YSZ substrates. The growth of single crystal orthorhombic κ-Ga2O3 films is confirmed by analyzing the scanning transmission electron microscopy nanodiffraction pattern. The chemical composition, surface stoichiometry, and bandgap energies of κ-Ga2O3 thin films grown on different substrates are studied by high-resolution x-ray photoelectron spectroscopy (XPS) measurements. The type-II (staggered) band alignments at three interfaces between κ-Ga2O3 and c-sapphire, AlN, and YSZ substrates are determined by XPS, with an exception of κ-Ga2O3/GaN interface, which shows type-I (straddling) band alignment.

Differential analyses of ginger extract implant coating material

Background: Different types of material were used as implants; the most common is titanium and its alloy, and recently zirconia acquired robust interest due to many desirable properties, Natural biocomposites recently received widespread attention as an active coating covering metallic implants due to their bioactivity, availability, and affordability. Aim: This study aims to present the evolvement and characterization of ginger extract materials overlying Yttria-stabilized tetragonal zirconia and PEEK substrate. Material and method: The methodology of the present study involved preparation of ginger extract powder twenty disc-shaped specimens with a dimension of 10 mm, from partially sintered Yttria-stabilized tetragonal zirconia polycrystal and PEEK . The naturally prepared ginger extract powder was deposited via cold spraying device. The prepared ginger extract characterized by particle size analyzer and ginger extract while The experimental specimens were characterized by, field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDX). Conclusion :naturally prepared ginger extract exhibit uniform distribution and good adherence to the samples Therefore, it can be used as a coating material for zirconia and PEEK implants with promising biological and mechanical properties.

Alternate-Target Layer-By-Layer Pulsed Laser Deposition of Epitaxial BiVO4 Thin Films

Bismuth vanadate (BiVO4) has emerged as one of the highest performing metal oxide photoelectrodes for solar energy-to-fuels applications [1, 2]. This achievement has been largely attributed to the development of high-quality synthesis techniques. Specifically, epitaxial synthetic routes to producing lattice-matched, near single-crystalline quality BiVO4 with minimal extrinsic defects have been essential to understand the fundamental and PEC properties of BiVO4 that are inaccessible by conventional bulk synthesis techniques. In addition, epitaxial synthesis may also be employed as a strategy to further improve the PEC properties of BiVO4 through, for instance, altering the band structure and enhancing the carrier dynamics by strain engineering. Hence, the ability to produce high-quality single-phase epitaxial BiVO4 films is desirable.To date, molecular beam epitaxy (MBE), chemical vapor deposition (CVD), and pulsed laser deposition (PLD) [3] have been used to fabricate epitaxial BiVO4 thin films, with PLD having the advantage of relatively simple experimental setup and material versatility. However, an oft-noted drawback in conventional PLD using single oxide targets is off-stoichiometry in the deposited films; this is especially so for BiVO4 which requires a Bi-rich compound target to achieve a stoichiometric BiVO4 film [4]. This problem is also expected in general for multinary oxides composed of elements with very different ablation properties. To alleviate the limitations of conventional PLD, we employ for the first time alternate-target layer-by-layer PLD as a more elegant approach to produce high quality epitaxial BiVO4 films. Briefly, constituent oxide targets are alternately ablated by an excimer laser (λ= 248 nm) to build the desired film one unit cell thick at a time. Stoichiometry is controlled by the number of shots corresponding to a specified laser fluence for the constituent oxide target.To demonstrate the method, we deposited epitaxial BiVO4 films onto (001)-oriented yttrium-stabilized zirconia (YSZ) using 4N-pure Bi2O3 and V2O5 targets. Films grown are single phase BiVO4 as shown by x-ray diffraction. Out-of-plane diffraction peaks indexed to BiVO4(00l) suggests epitaxy of the film onto the substrate; reciprocal space maps of the asymmetric BiVO4(208) and YSZ(204) peaks further confirm the BiVO4(001) || YSZ(001) epitaxial relationship (top figure). Rocking curves of the BiVO4 (004) peak (FWHM ~ 0.015-0.041) indicate high crystalline perfection of the BiVO4 film, almost approaching that of the YSZ substrate (FWHM ~ 0.010). Thickness dependent-rocking curve studies reveal that BiVO4 films are strained to the substrate for film thicknesses under 22 nm; above this critical thickness, film relaxation ensues. In turn, the resulting optoelectronic properties of the BiVO4 film is dictated by its relaxation state. The optical band gap narrows with film relaxation as observed with spectroscopic ellipsometry. Moreover, steady-state photoluminescence emission spectroscopy reveals a sub-bandgap state (A 2, bottom figure) associated with strained BiVO4 films, on top of a state consistent with band-to-band recombination (B1 ). A higher energy sub-bandgap state (A 1, bottom figure) develops as the film relaxes. The implications of the relaxation state on the charge carrier dynamics and photoelectrochemical properties of BiVO4 will be discussed. Figure: (top) reciprocal space maps of the asymmetric BiVO4(208) and YSZ(204) peaks; (bottom) photoluminescence emission spectra of strained and relaxed BiVO4 films.

Wetting of substoichiometric YSZ2-x by molten Sn-based active alloys at 800–900 °C

The wetting of Sn–8Zr, Sn–4Zr–4Ti, and Sn–8Ti on a substoichiometric YSZ2-x (yttria-stabilized substoichiometric zirconia) substrate was studied using a modified sessile drop method at 800–900 °C. The Sn–4Zr–4Ti/YSZ2-x system had the best final wettability (approximately 32°, 27°, and 22° at 800, 850, and 900 °C, respectively), satisfying the brazing wetting requirements. When Zr-containing alloys contacted the YSZ2-x substrate, the decomposition of YSZ2-x induced the formation of Sn2Zr and more non-metallic YSZ2-y. The final wettability was determined using Sn2Zr, YSZ2-y, and the adsorption of Zr (and/or Ti). Titanium in the Sn–8Ti/YSZ2-x system inhibited the massive decomposition of YSZ2-x, maintained the original metallicity, and, together with the adsorption of Ti, contributed to the final wettability. A scalar law analysis indicated that the wetting activation energies of the Sn–4Zr–4Ti/YSZ2-x and Sn–8Ti/YSZ2-x systems were 197 and 243 kJ/mol, corresponding to the formation of Sn–Zr and Ti–Zr chemical bonds during the liquid-solid interface formation, respectively.

Structural evolution of epitaxial CeO2-HfO2 thin films using atomic-scale observation: Formation of ferroelectric phase and domain structure

We investigated the structural evolution of 0.1CeO2–0.9HfO2 epitaxial films upon thermal annealing using X-ray diffraction and scanning transmission electron microscopy. The films were deposited via a sputtering method at room temperature onto (001)yttria-stabilized zirconia substrates and subsequently annealed. The crystalline phase of the deposited films changed from amorphous to highly symmetric phase (tetragonal and/or cubic phases) and then to orthorhombic with increasing annealing temperature. Isothermal annealing at 900 °C resulted in a series of transitions from the highly symmetric phase to a mixture of highly symmetric and orthorhombic phases, and finally to the orthorhombic phase as a function of time. Atomic-scale observations revealed the formation of nanosized orthorhombic domains within the dominant tetragonal phase; their number density and size increased with the annealing time. However, in-situ transmission electron microscopy of the crystallized film with the dominant orthorhombic phase revealed that the orthorhombic phase transformed back to the tetragonal phase above 540 °C upon reheating. Therefore, the tetragonal phase is a prerequisite for forming the orthorhombic phase, and the tetragonal-to-orthorhombic phase transition is reversible. Thus, this study offers a strategy to control the formation of tetragonal and orthorhombic phases of Ce-substituted HfO2 ferroelectric films by optimizing the annealing conditions.

Enhancement of transparency in epitaxially-grown p-type SnO films by surface-passivation treatment in a Na2S aqueous solution

We report on the epitaxial growth of (001)-oriented SnO films on yttria-stabilized zirconia (100) substrates by pulsed-laser deposition and the impact of surface-passivation treatment on the optical transparency. The films immersed in a Na2S aqueous solution exhibited average visible transmittance higher than that of the as-grown ones by ∼18% despite negligibly small variations in the crystalline structure, p-type conductivity, and composition. Based on these results, the enhanced visible transmittance can be attributed to the suppression of midgap states near the film surface. The extended treatment resulted in conversion to a SnS phase, demonstrating a facile anion-exchange reaction.

Ferroelectric and piezoelectric properties of 100 nm-thick CeO2-HfO2 epitaxial films

Scaling up the film thickness of HfO2-based ferroelectrics is an important factor leading to their potential application in piezoelectric devices. In this paper, we report the ferroelectric and piezoelectric properties of 100 nm-thick 0.1CeO2-0.9HfO2 films, epitaxially grown on (001) indium-tin-oxide//(001)yttria-stabilized zirconia substrates. The crystal structure was investigated using x-ray diffraction and scanning transmission electron microscopy (STEM). These analyses revealed that the polar orthorhombic phase was stabilized, even at a thickness of 100 nm, whereas the formation of a nonpolar monoclinic phase was suppressed. In addition, the elemental mappings obtained by STEM–energy dispersive x-ray spectroscopy revealed that the film was compositionally uniform across its thickness. The chemical state of Ce in the polar orthorhombic domain was investigated using STEM–electron energy loss spectroscopy, which revealed the coexistence of Ce4+ and Ce3+. In addition, pinched polarization-electric field loops were observed, and their shapes were found to remain unaltered even after 109 electric field cycles. The strain-electric field curves originating from ferroelectricity were observed before and after the electric field cycling, and the high-field observed strain, Smax/Emax, was found to be approximately 7.2 pm/V. These results demonstrate that thicker CeO2-HfO2 ferroelectric films are promising candidates for use as piezoelectric materials.

Natural preparation of rice husk-derived silica and eggshell-derived calcium carbonate composite as a coating material for dental implant

Background: The world is in front of two emerging problems being scarceness of virgin re-sources for bioactive materials and the gathering of waste production. Employment of the surplus waste in the mainstream production can resolve these problems. The current study aimed to prepare and characterize a natural composite CaO-SiO2 based bioactive material derived from naturally sustained raw materials. Then deposit this innovative novel bioactive coating composite materials overlying Yttria-stabilized tetragonal zirconia substrate. Mate-rials and method; Hen eggshell-derived calcium carbonate and rice husk-derived silica were extracted from natural resources to prepare the composite coating material. The manufac-tured powder was characterized via Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM), X-ray fluorescence (XRF), X-ray diffraction (XRD) and particle size analyzer. The bioactive composite was deposited through radiofre-quency (Rf) reactive magnetron sputtering overlying disc-shaped samples with a dimension of 10 mm diameter were prepared from partially sintered Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP). Results: The particle size of the rice husk-derived ranged between (480.4 – 606.1) nm with a mean particle diameter of 541 nm. The eggshell derived calcium carbonate powder presented a particle size between (266.4-336) nm and a mean particle diameter of 299.9 nm. The XRD data revealed the crystalline nature and phase composition of the natural prepared calcium carbonate powder and demonstrate the monocrystalline nature of natural SiO2. FTIR spectrometer showed the emergence of novel spectra separated from the two innovative components. XRF analysis revealed that 99.4% of the rice husk is SiO2 while eggshell-derived powder is mainly composed of calcium oxide. Fe-SEM images of the coated zirconia exhibited average thickness of the natural CaCO3/SiO2 coat layer may reach to12.84 µ. Conclusion: The prepared composite derived from natural resource waste is suitable to be utilized as a coating material for ceramic dental implants with promising biological and mechanical properties.

Molecular beam epitaxy of single-crystalline bixbyite (In1−xGax)2O3 films ( x≤0.18 ): Structural properties and consequences of compositional inhomogeneity

In this work, we show the heteroepitaxial growth of single-crystalline bixbyite (In$_{1-x}$Ga$_x$)$_2$O$_3$ films on (111)-oriented yttria-stabilized zirconia substrates using plasma-assisted molecular beam epitaxy under various growth conditions. A pure In$_2$O$_3$ buffer layer between the substrate and (In$_{1-x}$Ga$_x$)$_2$O$_3$ alloy is shown to result in smoother film surfaces and significantly improved crystallinity. Symmetric out-of-plane 2$\theta - \omega$ x-ray diffraction scans show a single (111) crystal orientation and transmission electron microscopy confirms the single-crystallinity up to $x = 0.18$ and only slight film quality deterioration with increasing Ga content. Partially relaxed layers are demonstrated via reciprocal space mapping with lattice parameters fitting well to Vegard's law. However, the Ga cations are not evenly distributed within the films containing nominally $x > 0.11$: inclusions with high Ga density up to $x = 0.50$ are observed within a "matrix" with $x \approx 0.08$. The cubic bixbyite phase is preserved, in both the "matrix" and the inclusions. Moreover, for $x \geq 0.11$, both the Raman phonon lines as well as the optical absorption onset remain nearly constant. Hard x-ray photoelectron spectroscopy measurements also indicate a widening of the band gap and exhibit similar saturation of the Ga 2p core level position for high Ga contents. This saturation behavior of the spectroscopic properties further supports the limited Ga incorporation into the "matrix" of the film.

Fabrication of Fluorite and Perovskite Functional Films by Solution Spray Pyrolysis

Solution Spray Pyrolysis (SST) was successfully implemented to fabricate thin perovskite and fluorite films on dense Yttria Stabilized Zirconia (YSZ) and Lanthanum Strontium Ferrate (LSF70) substrates. These composite structures are ubiquitous in solid oxide fuel cells and electrolyzers, CO gas sensors and ceramic membranes. With this technique, successful in situ manipulation of the film’s functional characteristics such as porosity and thickness is easily achieved by adjusting its functional parameters.In the present contribution, we report on the optimization of the physicochemical parameters of this open atmosphere technique with respect to the substrate temperature and deposition time for the fabrication of films of suitable morphology. Sintered films were characterized by XRD and SEM while thermal analysis was performed on the precursor salts. In addition, AC Impedance analysis was performed on some CGO films in order to assess their electron blocking capability in contact with the LSF substrates.

Thermal energy evolution and mechanical deformation of monocrystalline yttria-stabilized zirconia nanoparticles in aerosol deposition processes

Aerosol deposition (AD) is a coating process wherein aerosol particles are impacted on a target substrate. There are fundamental differences between the AD process (cold impact), where particle translational kinetic energy is high and thermal energy is low, and thermal spray deposition (thermal impact), where translational energy is lower but thermal energy is high. To better compare cold and thermal impact effects on particles, we carried out molecular dynamics simulations using yttria-stabilized zirconia (YSZ) nanoparticles on YSZ substrates as a model system. We performed cold impact simulations at 300 K with variable impact velocity in the 500 ms−1–1500 ms−1 range to understand how increasing translational kinetic energy affects thermal energy and mechanical evolution. We then performed thermal impact simulations at variable temperature and impact velocity, but where the total kinetic energy of the nanoparticle was equivalent to that of a 300 K, 1000 ms−1 impact. In cold impact, the temperature increases in YSZ nanoparticles at a rate of 1013–1014Ks−1, and large temperature gradients result. Conversely, in thermal impact, nanoparticle temperatures remain uniform. The temperature gradients during cold impact coincide with plastic deformation in nanoparticles, while with larger thermal energies, plastic deformation is reduced.

Vacuum Brazing of Metallized YSZ and Crofer Alloy Using 72Ag-28Cu Filler Foil.

The study focused on dissimilar brazing of metallized YSZ (Yttria-Stabilized Zirconia) and Crofer alloy using BAg-8 (72Ag-28Cu, wt%) filler foil. The YSZ substrate was metallized by sequentially sputtering Ti (0.5/1 μm), Cu (1/3 μm), and Ag (1.5/5 μm) layers, and the Crofer substrate was coated with Ag layers with a thickness of 1.5 and 5 μm, respectively. The BAg-8 filler demonstrated excellent wettability on both metallized YSZ and Crofer substrates. The brazed joint primarily consisted of Ag-Cu eutectic. The metallized Ti layer dissolved into the braze melt, and the Ti preferentially reacted with YSZ and Fe from the Crofer substrate. The globular Fe2Ti intermetallic compound was observed on the YSZ side of the joint. The interfacial reaction of Ti was increased when the thickness of the metallized Ti layer was increased from 0.5 to 1 μm. Both brazed joints were crack free, and no pressure drop was detected after testing at room temperature for 24 h. In the YSZ/Ti(0.5μ)/Cu(1μ)/Ag(1.5μ)/BAg-8(50μ)/Ag(1.5μ)/Crofer joint tested at 600 °C, the pressure of helium decreased from 2.01 to 1.91 psig. In contrast, the helium pressure of the YSZ/Ti(1μ)/Cu(3μ)/Ag(5μ)/BAg-8(50μ)/Ag(5μ)/Crofer joint slightly decreased from 2.02 to 1.98 psig during the cooling cycle of the test. The greater interfacial reaction between the metallized YSZ and BAg-8 filler due to the thicker metallized Ti layer on the YSZ substrate was responsible for the improved gas-tight performance of the joint.

Mixed potential type YSZ-based NO2 sensors with efficient three-dimensional three-phase boundary processed by electrospinning

A mixed potential type yttria-stabilized zirconia (YSZ)-based NO2 sensor attached with NiO sensing electrode (SE) with efficient three-phase boundary (TPB) processed by electrospinning technology was fabricated. The effect of the structure and area of TPB on the gas sensing performance of the sensor was investigated systematically. The YSZ nanofiber array was directly deposited on YSZ substrate by electrospinning method to construct efficient three-dimensional TPB. The sensor (S30) based on YSZ substrate processed by electrospinning method with the flow rate of 1.5 mL/h for 15 min and NiO-SE exhibited the highest sensitivity (77.4 mV/decade) to 5–500 ppm NO2 at 510 °C, which was 2.6 times as the sensor (S00) with unprocessed YSZ substrate. The response value of S30 to 100 ppm NO2 could reach 109 mV at 510 °C, which increased about 51 mV comparing with S00. Moreover, the sensor (S30) also displays fast response and recovery rates, good repeatability, excellent selectivity, moisture resistance and long-term stability. The elevated NO2 sensing performance of the sensor is attributed to more active sites of electrochemical reactions by increased area of three-dimensional TPB.

Thin-film chemical expansion of ceria based solid solutions: laser vibrometry study

Abstract The chemical expansion of Pr0.1Ce0.9O2–δ (PCO) and CeO2–δ thin films is investigated in the temperature range between 600 °C and 800 °C by laser Doppler vibrometry (LDV). It enables non-contact determination of nanometer scale changes in film thickness at high temperatures. The present study is the first systematic and detailed investigation of chemical expansion of doped and undoped ceria thin films at temperatures above 650 °C. The thin films were deposited on yttria stabilized zirconia substrates (YSZ), operated as an electrochemical oxygen pump, to periodically adjust the oxygen activity in the films, leading to reversible expansion and contraction of the film. This further leads to stresses in the underlying YSZ substrates, accompanied by bending of the overall devices. Film thickness changes and sample bending are found to reach up to 10 and several hundred nanometers, respectively, at excitation frequencies from 0.1 to 10 Hz and applied voltages from 0–0.75 V for PCO and 0–1 V for ceria. At low frequencies, equilibrium conditions are approached. As a consequence maximum thin-film expansion of PCO is expected due to full reduction of the Pr ions. The lower detection limit for displacements is found to be in the subnanometer range. At 800 °C and an excitation frequency of 1 Hz, the LDV shows a remarkable resolution of 0.3 nm which allows, for example, the characterization of materials with small levels of expansion, such as undoped ceria at high oxygen partial pressure. As the correlation between film expansion and sample bending is obtained through this study, a dimensional change of a free body consisting of the same material can be calculated using the high resolution characteristics of this system. A minimum detectable dimensional change of 5 pm is estimated even under challenging high-temperature conditions at 800 °C opening up opportunities to investigate electro-chemo-mechanical phenomena heretofore impossible to investigate. The expansion data are correlated with previous results on the oxygen nonstoichiometry of PCO thin films, and a defect model for bulk ceria solid solutions is adopted to calculate the cation and anion radii changes in the constrained films during chemical expansion. The constrained films exhibit anisotropic volume expansion with displacements perpendicular to the substrate plane nearly double that of bulk samples. The PCO films used here generate high total displacements of several 100 nm’s with high reproducibility. Consequently, PCO films are identified to be a potential core component of high-temperature actuators. They benefit not only from high displacements at temperatures where most piezoelectric materials no longer operate while exhibiting, low voltage operation and low energy consumption.

Flexible All-Inorganic Room-Temperature Chemiresistors Based on Fibrous Ceramic Substrate and Visible-Light-Powered Semiconductor Sensing Layer.

As the most extensively used gas‐sensing devices, inorganic semiconductor chemiresistors are facing great challenges in realizing mechanical flexibility and room‐temperature gas detection for developing next‐generation wearable sensing devices. Herein, for the first time, flexible all‐inorganic yttria‐stabilized zirconia (YSZ)/In2O3/graphitic carbon nitride (g‐C3N4) (ZIC) gas sensor is designed by employing YSZ nanofibers as substrate, and ultrathin In2O3/g‐C3N4 heterostructures as active sensing layer. The YSZ substrate possesses small nanofiber diameter (310 nm), ultrafine grain size (23.9 nm), and abundant dangling bonds, endowing it with striking mechanical flexibility and strong adhesion with In2O3/g‐C3N4 sensing layer. Meanwhile, the ultrathin thickness (≈7 nm) of In2O3/g‐C3N4 ensures that the inorganic sensing layer has tiny linear strain along with the deformation of flexible YSZ substrate, thereby enabling unusual bending capacity. To address the operating temperature issue, the gas sensor is operated by using a visible‐light‐powered strategy. Under visible‐light illumination, the flexible ZIC sensor exhibits a perfectly reversible response/recovery dynamic process and ultralow detection limit of 50 ppb to toxic nitrogen dioxide at room temperature. This work not only provides an insight into the mechanical flexibility of inorganic materials, but also offers a valuable reference for developing other flexible inorganic‐semiconductor‐based room‐temperature gas sensors.

(Invited) Additive Manufacturing of Mixed Potential Gas Sensors for Natural Gas Emissions Monitoring

Additive manufacturing (AM) of ceramic materials offers a promising route to manufacturing high temperature electrochemical devices at small prototyping scales where mass production techniques have excessively high tooling setup cost and time.1 AM also enables the production of components with customizable geometries unavailable to traditional techniques. Mixed Potential Electrochemical Sensors (MPES) are an attractive technology for environmental monitoring applications due to their robustness, low cost, and tunable selectivity.2 MPES devices consist of two or more dissimilar material electrodes in a solid-state electrolyte where the mixed potential difference between the electrodes is used as a sensing parameter. Previously, we have demonstrated the capability to print two-electrode MPES devices on laminated yttria stabilized zirconia (YSZ) substrates and their sensitivity to NOx and NH3.3 We are currently pursuing the development of MPES systems for environmental monitoring of natural gas emissions from pipeline infrastructure. The system will include MPES devices manufactured by additive manufacturing which interface with wireless data acquisition hardware to perform remote sensing. We have used AM to evaluate a wide range of materials and geometries for optimization of sensitivity, selectivity, and stability.Material extrusion with a multi-print-head Hyrel System 30M syringe printer (Figure 1a) was used to deposit the YSZ substrate material, YSZ porous electrolyte, and electrodes consisting of Au, Pt, La0.87Sr0.13CrO3 (LSC), and Indium Tin Oxide (ITO). YSZ, ITO, and LSC pastes were formulated by mixing powders into resins. A UV-curable resin was used for the printing of YSZ substrates under continuous 365 nm illumination. Pt and Au inks were also extruded from a syringe onto the substrate (Figure 1b) and the final 4-electrode device is shown in Figure 1c. Parameters we optimized included paste solids loading, addition of powder dispersants, the incident power of the UV-curing process. The sensor response to CH4, simulated natural gas, NH3 and H2 were evaluated for sensitivity and selectivity in single gas and binary mixtures at temperatures of 450-600oC (Figure 1d) . Acknowledgments: This project was supported by US Department of Energy Office of Fossil Energy through award DE-FE0031864. References (1) Travitzky, N.; Bonet, A.; Dermeik, B.; Fey, T.; Filbert-Demut, I.; Schlier, L.; Schlordt, T.; Greil, P. Adv. Eng. Mater. 2014, 16 (6), 729–754.(2) Garzon, F. H.; Mukundan, R.; Brosha, E. L. Solid State Ionics 2000, 136–137, 633–638.(3) Tsui, L.; Benavidez, A.; Evans, L.; Garzon, F. H. Prog. Addit. Manuf. 2018, 4, 13-21. Figure 1. (a) The Hyrel System 30M syringe dispense printer with two UV assisted dispensing heads. (b) Extrusion of Pt ink from a syringe printer onto partially sintered YSZ substrate. (c) Photograph of a completed multi-electrode MPES device. (d) Sensor response to 1000-4000 ppm CH4 in air at 550oC. Figure 1

Ag/Ce0.9Gd0.1O2- δ Based Vertically Aligned Nanocomposite Thin Film Electrodes for Low-Temperature Solid Oxide Cells

Low temperature solid oxide cells (LT-SOCs, 300-500°C) have become the "next generation" technology following the commercialized high temperature SOCs (650–850 °C). The current research is focused on screening new materials and microstructural designs that are ideal for low-temperature operations. This study explores the vertically aligned nanocomposite (VAN) heterostructure design, which has been shown to provide novel properties and new functionalities at the heterointerfaces of two oxide materials.1 In this design, we combine two materials known to show exceptionally fast electrokinetics at low temperatures. However, instead of two oxide materials, we explore a combination of electronically conducting metal and an ionically conducting oxide. The electrode composed of Ag and Ce0.9Gd0.1O2-d (CGO) is deposited epitaxially on oriented yttria-stabilized zirconia substrates by pulsed laser deposition. Silver is a highly active catalyst for oxygen reduction reactions (ORR), exhibits high electrical conductivity at low temperatures and is resistant to oxidation in air, but has a relatively low melting point and agglomerates easily in air. Therefore, it is necessary to prevent Ag agglomeration during operation. Addition of CGO is expected to (i) stabilize Ag by surrounding it through vertically grown columns and (ii) extend the ionically conducting path onto the cathode and share the oxygen ion diffusion pathway with Ag.2 Preliminary results show successful growth of ~40 nm thick oriented Ag/CGO VAN films. The investigations will be complemented with electrochemical performance and stability measurements using impedance spectroscopy. This study will provide insights into enhanced ORR performance at low temperatures by controlling crystal orientation and strain tuning at the metal/oxide VAN heterointerfaces. J. Huang, W. Li, H. Yang and J. L. MacManus-Driscoll, MRS Bull., 2021, 46, 159–167.H. R. Choi, K. C. Neoh, H. J. Choi, G. D. Han, D. Y. Jang, D. Kim and J. H. Shim, J. Power Sources, 2018, 402, 246–251.