Synchrotron Technique Research Articles

Sulfur speciation in dacitic melts using X-ray absorption near-edge structure spectroscopy of the S K-edge (S-XANES): Consideration of radiation-induced changes and the implications for sulfur in natural arc systems

Abstract The synchrotron technique of micro X-ray absorption near-edge structure spectroscopy at the sulfur K-edge (S-XANES) provides a unique opportunity to measure the proportion of different oxidation states of sulfur (S) in silicate glasses. Although applied extensively in the analysis of basaltic silicate glasses, few S-XANES studies have investigated variations in S oxidation states with fO2 in felsic silicate glasses. In addition, no study has systematically compared the S-XANES results obtained from the same samples at different photon flux densities to quantify the relationship between exposure time and changes in S speciation in silicate glass, as has been done for Fe and V. This study evaluates observed differences in S speciation measured in experimentally produced H2O-saturated dacitic glasses over a range of reducing to oxidizing conditions (from log fO2 = ΔFMQ-0.7 to ΔFMQ+3.3; FMQ is the fayalite-magnetite-quartz mineral redox buffer) and equilibrated at 1000°C and 300 MPa. S-XANES spectra were collected at three different photon flux densities using three microspectroscopy beamlines. As is observed in S-XANES analyses of basaltic silicate glasses, beam-induced changes to the S6+/ΣS are observed as a function of photon flux density and beam exposure time. Our results demonstrate that silicate glasses of dacitic composition undergo beam-induced photo-reduction in samples equilibrated at ΔFMQ > +1.75 and photo-oxidation if equilibrated at ΔFMQ < +1. The time required to observe beam-induced changes in the spectra varies as a function of flux density, and our study establishes an upper photon density limit at ~1.0 × 1012 photons/μm2. The S6+/ΣS calculated from spectra collected below this absorbed photon limit at intermediate flux densities (~1−4 × 109 photons/sec per μm2) are affected by beam damage, as no conditions were found to be completely free of beam-induced changes. However, the S6+/ΣS ratios calculated below the limit at intermediate flux densities are consistent with thermodynamic constraints, demonstrating that S6+/ΣS ratios calculated from S-XANES spectra can be considered reliable for estimating the oxygen fugacity. Our results carry important implications for the S budget of felsic magmas and dissolution mechanisms in evolved melts. While our results from all three flux densities show the presence of S4+ dissolved in relatively oxidized (ΔFMQ > +1.75) dacitic glass, even in the spectra exposed to the lowest photon densities, we are unable to rule out the possibility that the S4+ signal is the result of instantaneous X-ray irradiation induced beam damage using S-XANES alone. When our spectra are compared to S-XANES spectra from basaltic silicate glasses, important differences exist in the solubility of S2- and S6+ between dacitic silicate melts, pointing to differences in solubility mechanisms as melt composition changes. This study highlights the need for further investigation into beam damage systematics, presence of S4+, and the solubility mechanisms of different oxidation states of S as silicate melt composition changes.

Performance Evaluation of Focal Plane Array (FPA)-FTIR and Synchrotron Radiation (SR)-FTIR Microspectroscopy to Classify Rice Components.

The development of biochemical analysis techniques to study heterogeneous biological samples is increasing. These techniques include synchrotron radiation Fourier transform infrared (SR-FTIR) microspectroscopy. This method has been applied to analyze biological tissue with multivariate statistical analysis to classify the components revealed by the spectral data. This study aims to compare the efficiencies of SR-FTIR microspectroscopy and focal plane array (FPA)-FTIR microspectroscopy when classifying rice tissue components. Spectral data were acquired for mapping the same sample areas from both techniques. Principal component analysis and cluster imaging were used to investigate the biochemical variations of the tissue types. The classification was based on the functional groups of pectin, protein, and polysaccharide. Four layers from SR-FTIR microspectroscopy including pericarp, aleurone layer, sub-aleurone layer, and endosperm were classified using cluster imaging, while FPA-FTIR microspectroscopy could classify only three layers of pericarp, aleurone layer, and endosperm. Moreover, SR-FTIR microspectroscopy increased the image contrast of the biochemical distribution in rice tissue more efficiently than FPA-FTIR microspectroscopy. We have demonstrated the capability of the high-resolution synchrotron technique and its ability to clarify small structures in rice tissue. The use of this technique might increase in future studies of tissue characterization.

Strain Evolution in Pt-Ni Alloy Nanoparticles during Electrochemical Ni Leaching Revealed By Bragg Coherent Diffraction Imaging

Alloy catalysts such as Pt-M (M: other metal elements) have been extensively developed to improve the sluggish oxygen reduction reaction (ORR) that limits the efficiencies of fuel cells and metal-air batteries. Their catalytic activity is potentially enhanced by strain induced in a nearly pure Pt "shell" formed by dissolving the alloyed metal (M) from the surface. It is, therefore, of great importance to reveal the strain distribution on the Pt shell in situ so that we can exploit this mechanism to design new alloy catalysts. Yet, it has been challenging to analyze the strain on the shell because it inevitably requires a technique that can image the strain field of the nanoparticles with high spatial resolution.In this study,1 we successfully revealed the strain of the exemplary Pt-Ni alloy nanoparticles in detail from the 3D images obtained by using a novel synchrotron technique, “Bragg Coherent X-ray Diffraction Imaging” (BCDI), which can directly image minute atomic displacement field owing to the X-ray coherence. Pt-Ni nanoparticles with compositions of Pt2Ni3 (Ni rich), Pt1Ni1 (moderate Ni), and Pt3Ni2 (Ni poor) were observed by BCDI during cyclic voltammetry cycles, in which the less noble metal Ni electrochemically leached from the alloy. This cycling induced tensile strain inside particles in all the compositions, implying that the formation of a Pt shell on the surface strained the core of the particle because of the lattice mismatch between the Pt-Ni alloys and Pt. The strain in the shell was evaluated from a core-shell elastic model using the parameters obtained in the 3D images.A compressive circumferential strain in the shell was observed in all the compositions, and the Pt1Ni1 particle showed the largest compressive circumferential strain of 5%. Since the compressive strain is reported to facilitate the enhanced ORR,2 the compositional dependence of the strain magnitude observed in this study was in excellent agreement with the previous study performed with nm-size particles where Pt1Ni1 exhibits the highest activity among a wide range of compositions.3 A similar strain-activity relation was also inferred in a powder X-ray diffraction studies of core-shell Pt x Co1-x alloys,4 suggesting it is a widely applicable phenomenon. The present study demonstrated that the strain on alloy nanoparticles can be quantitatively determined by BCDI during electrochemical reactions, which enables us to exploit surface strain in designing a wide range of electrocatalysts. T. Kawaguchi et al., Nano Letters, 21, 5945–5951 (2021).H. Wang et al., Science, 354, 1031–1036 (2016).C. Wang et al., Advanced Functional Materials, 21, 147–152 (2011).D. Wang et al., Nature Materials, 12, 81–87 (2013).

(Invited) Operando Measurement of Heterogeneities in All-Solid-State Li Battery Electrodes

All-solid-state Li batteries are under intense research and development due to their potential to (a) replace flammable organic liquid electrolytes with solid materials, and (b) increase energy density by allowing Li metal anodes and resulting in a more compact battery.[1]Several types of Li+-conducting solid electrolytes are being studied, e.g. sulfides, oxides, phosphates, polymers, and various composites of these.[2] While polymers are very processable, they have low conductivities, generally <10-4 S/cm. Sulfides have high conductivities, >10-2 S/cm, but are unstable materials and require cells to be under high compression to get good cycling results.[3] Oxides and phosphates have good conductivity, but are hard and brittle, forming poor interfaces with electrode active materials. The ideal combination of solid electrolyte and active material remains elusive, but work continues.An additional challenge looms for the design of all-solid-state electrodes, as reaction distributions in battery electrodes are often heterogeneous, resulting in uneven utilization of active materials.[4] Uneven reaction distributions are generally the result of an imbalance between electronic and ionic transport in the cell, but can also be caused by other resistances such as those introduced by insulating layers surrounding active materials. In this talk I will report our experimental results measuring heterogeneous phenomena in all-solid-state batteries. We have employed electrochemical impedance spectroscopy (EIS) as well as energy dispersive X-ray diffraction (EDXRD). EDXRD is a high-energy synchrotron technique that allows the interiors of batteries to be profiled in a tomographic way during battery operation. We use this to directly observe heterogeneous lithiation gradients across the thickness of cathodes in all-solid-state batteries. We will focus on cells with sulfide electrolytes, such as Li6PS5Cl and Li6.6Ge0.6Sb0.4S5I. Heterogeneous structural stability of the electrolyte itself will also be discussed.[5] Acknowledgments We acknowledge financial support from the National Science Foundation under Award Number CBET-ES-1924534.

A guide into the world of high-resolution 3D imaging: the case of soft X-ray tomography for the life sciences.

In the world of bioimaging, every choice made determines the quality and content of the data collected. The choice of imaging techniques for a study could showcase or dampen expected outcomes. Synchrotron radiation is indispensable for biomedical research, driven by the need to see into biological materials and capture intricate biochemical and biophysical details at controlled environments. The same need drives correlative approaches that enable the capture of heterologous but complementary information when studying any one single target subject. Recently, the applicability of one such synchrotron technique in bioimaging, soft X-ray tomography (SXT), facilitates exploratory and basic research and is actively progressing towards filling medical and industrial needs for the rapid screening of biomaterials, reagents and processes of immediate medical significance. Soft X-ray tomography at cryogenic temperatures (cryoSXT) fills the imaging resolution gap between fluorescence microscopy (in the hundreds of nanometers but relatively accessible) and electron microscopy (few nanometers but requires extensive effort and can be difficult to access). CryoSXT currently is accessible, fully documented, can deliver 3D imaging to 25 nm resolution in a high throughput fashion, does not require laborious sample preparation procedures and can be correlated with other imaging techniques. Here, we present the current state of SXT and outline its place within the bioimaging world alongside a guided matrix that aids decision making with regards to the applicability of any given imaging technique to a particular project. Case studies where cryoSXT has facilitated a better understanding of biological processes are highlighted and future directions are discussed.

3D mapping of orientation variation and local residual stress within individual grains of pearlitic steel using synchrotron dark field X-ray microscopy

Assessing the local residual stress and orientation with nanometer resolution within embedded steel grains has remained challenging. Here we use an advanced synchrotron technique, dark field X-ray microscopy to map 3D lattice variations, including both the crystallographic orientation and lattice strain, within two pro-eutectoid ferrite grains in pearlitic steel. We found an orientation variation up to 0.5° and compressive elastic strain up to 1.8 × 10−3 are present in the as-manufactured sample. There is no direct correlation between the measured compressive strain and lattice orientation. The origin of the variations and their influence on the manufacturing process and mechanical properties are discussed.

Influence of Metal-Alkyls on Early-Stage Ethylene Polymerization over a Cr/SiO2 Phillips Catalyst: A Bulk Characterization and X-ray Chemical Imaging Study.

The Cr/SiO2 Phillips catalyst has taken a central role in ethylene polymerization since its invention in 1953. The uniqueness of this catalyst is related to its ability to produce broad molecular weight distribution (MWD) PE materials as well as that no co‐catalysts are required to attain activity. Nonetheless, co‐catalysts in the form of metal‐alkyls can be added for scavenging poisons, enhancing catalyst activity, reducing the induction period, and tailoring polymer characteristics. The activation mechanism and related polymerization mechanism remain elusive, despite extensive industrial and academic research. Here, we show that by varying the type and amount of metal‐alkyl co‐catalyst, we can tailor polymer properties around a single Cr/SiO2 Phillips catalyst formulation. Furthermore, we show that these different polymer properties exist in the early stages of polymerization. We have used conventional polymer characterization techniques, such as size exclusion chromatography (SEC) and 13C NMR, for studying the metal‐alkyl co‐catalyst effect on short‐chain branching (SCB), long‐chain branching (LCB) and molecular weight distribution (MWD) at the bulk scale. In addition, scanning transmission X‐ray microscopy (STXM) was used as a synchrotron technique to study the PE formation in the early stages: allowing us to investigate the produced type of early‐stage PE within one particle cross‐section with high energy resolution and nanometer scale spatial resolution.

Phonon dispersion of bulk Ge-rich SiGe: inelastic X-ray scattering studies

Group IV semiconductors, such as SiGe with a higher Ge fraction, are attracting attention as next-generation materials for high-mobility channel or thermal conductivity devices. Thus, we investigated the phonon dispersions of a Si1–xGex (x = 0.72) alloy crystal by the inelastic X-ray scattering (IXS) method. In this method, measurement with an X-ray beam with a small spot size of 75 μm and resolution of millielectronvolts is possible due to the synchrotron technique. The longitudinal and transverse phonon spectra of optical and acoustic modes were measured from the Γ to the X point in the phonon energy band (0–70 meV) with millielectronvolt energy resolution. SiGe showed dispersion characteristics similar to those of Si and Ge crystals. It was confirmed that the IXS method is useful for obtaining properties of phonon dispersion.

Resonant slow extraction with constant optics for improved separatrix control at the extraction septum

Losses and component activation are limiting performance factors for slow extraction with high-power applications, and new techniques of loss-reduction, such as bent crystals, require a stable and narrow separatrix angular spread. Conventional tune-sweep slow extraction results in an optics change and an accompanying separatrix rotation through the spill. This can be compensated by a dynamic closed-orbit bump, but requires a high level of complexity for setting up and monitoring. For the Super Proton Synchrotron (SPS), a simpler and powerful new extraction technique has been developed and deployed, providing a mechanism to fix the machine optics and hence separatrix completely through the spill. The technique with the name constant optics slow extraction (COSE) relies on high chromaticity and scaling all machine settings with beam rigidity following the momentum distribution of the beam. In this paper we describe the new COSE concept and its successful operational deployment in the SPS during the 2018 run.

Surface Stabilization of O3-type Layered Oxide Cathode to Protect the Anode of Sodium Ion Batteries for Superior Lifespan.

SummaryEven though the energy density of O3-type layer-structured metal oxide cathode can fully reach the requirement for large-scale energy storage systems, the cycling lifespan still cannot meet the demand for practical application once it is coupled with a non-sodium-metal anode in full-cell system. Transition metal dissolution into the electrolyte occurs along with continuous phase transformation and accelerates deterioration of the crystal structure, followed by migration and finally deposition on the anode to form a vicious circle. Surface engineering techniques are employed to modify the interface between active materials and the electrolyte by coating them with a thin layer of AlPO4 ion conductor. This stable thin layer can stabilize the surface crystal structure of the cathode material by avoiding element dissolution. Meanwhile, it can protect the anode from increased resistance by suppressing the dissolution-migration-deposition process. This technique is a promising method to improve the lifetime for the future commercialization.

Polyamorphic transition in a transition metal based metallic glass under high pressure

Pressure-induced glass-glass transition (GGT) has been reported in a few rare-earth based and main-group metallic glasses (MGs), a process during which the compressibility decreases with the transformation from a low-density to a high-density amorphous state. Herein, we report an unexpected GGT behavior in Pd-based MGs under pressure, which is characterized by an anomalous increase in the compressibility with the pressure. State-of-the-art high-energy synchrotron technique, coupled with theoretical simulations, reveals that this unique GGT behavior is primarily caused by the change in bonding characteristics, i.e., some covalentlike atomic bonds in the as-prepared state change to metallic ones under high pressure, which also leads to the increase in the compressibility. Our current findings shed light on the understanding of the nature of polyamorphic transitions in MGs.

In-situ investigations of structural changes during cyclic loading of aluminium by high resolution reciprocal space mapping

A major failure reason for structural materials is fatigue-related damage due to repeatedly changing mechanical loads. During cyclic loading dislocations self-organize into characteristic ordered structures, which play a decisive role for the materials lifetime. These heterogeneous dislocation structures are identified by high resolution reciprocal space mapping. The synchrotron technique using high energy X-rays was applied successfully in-situ during cyclic deformation of macroscopic aluminium samples at the Advanced Photon Source to reveal the structural reorganization within single grains embedded in the bulk material during cyclic deformation. As evident from the changes in the radial profiles of four grains, the adaption of the deformation structure to cyclic deformation is completed already after 800 cycles. Individual subgrains have been followed through a 7350 tension–tension cycles while monitoring macroscopic stress and strain during cyclic loading. The elastic back strains of subgrains are Gaussian distributed with larger subgrains showing larger back strains. The detailed characterization of the microstructure during cyclic loading by in-situ monitoring of the internal structure within individual grains facilitates the understanding of materials behaviour during cyclic deformation.

(Invited) High-Sn Concentration MOCVD-Grown Strained GeSn Thin Films Evaluated Using HAXPES and XRD Base on Synchrotron Technique

1. Introduction GeSn alloy is an attractive material as a high hole mobility channel substituting Si and as a stressor for strained channels. Furthermore, modulation of band structure from indirect to direct gap by the increasing Sn composition up to 6-10 % is expected to improve the performance of optical devices [1, 2]. Then, a high-quality GeSn thin film with higher Sn concentration is a promising for higher performance and integrated devices on the Si platform. However, it has been difficult to increase Sn concentration, because the solubility limit of Sn within a GeSn film is considered to be approximately 1 atomic % [3]. Hence, a growth technique which enables the suppression of Sn segregation during GeSn growth and a characterization to analyze the surface segregation occurred with a thickness of several nm, are essential. For these purpose, we have developed a metal-organic chemical-vapor-deposition (MOCVD) method with new source gases that is safe, uniform, and industrially applicable [4]. In addition, we also investigated a hard X-ray photoelectron spectroscopy (HAXPES) and X-ray diffraction (XRD) on synchrotron technique to analyze thin GeSn films. In this presentation, we introduce high Sn concentration GeSn thin film exceeding 6% prepared by combining the new MOCVD growth and synchrotron analysis methods. 2. Experimental Thin GeSn films with the thickness of typically 30-100 nm were grown on (001) Ge substrates at low temperature (320-360 degrees) by the MOCVD method using Ge (t-C4H9GeH3) and specially prepared Sn ((C2H5)4Sn) source gases. The Sb was doped from the atmosphere with residual triisopropyl-antimony [(i-C3H7)3Sb]. The target compositions of Sn were 2%, 3%, 6%, respectively. To clarify the crystallinity of GeSn films, HAXPES and XRD were carried out at SPring-8. Since the inelastic mean free path (IMFP) is several times deeper than that for conventional X-ray photoelectron spectroscopy (XPS), HAXPES is expected to be useful to identify simultaneously the variation of chemical state at a surface part and the underlying bulk part of a GeSn film [5]. The Sn and Sb concentrations were calculated by the combination of Rutherford back-scattering spectroscopy (RBS) and secondary ion mass spectrometry (SIMS) measurements. Cross-sectional TEM was also carried out for the evaluation of the crystal quality. 3. Results and discussion Initially, we observed the splitting of the Sn3d5/2 spectrum into two peaks for 3% Sn composition GeSn film by the HAXPES measurement, whereas the spectrum of a low Sn composition (2%) GeSn film remained single (Fig.1). The binding energy of the newly split peak (M2) was lower than that of the Sn3d5/2 peak (M1) and the peak position of M1 approximately coincided with that of the 2% GeSn film. To clarify the newly split Sn3d5/2 peak (M2), total reflection mode HAXPES (TR-HAXPES) measurement was also carried out for the 3% GeSn film. As a result, only a single Sn3d5/2 spectrum was observed by the measurement. Since the position of the observed peak by the TR-HAXPES, closely coincided with the split peak (M2), the M2 was identified as a peak derived from the Sn segregation formed at the film surface. Hence, it is concluded that depth profile characterization of the Sn chemical state within a GeSn film possible by combining the HAXPES and TR-HAXPES measurements. In order to further increase the Sn concentration, we employed Sb as a surfactant [6]. As a result, neither extreme change of XRD spectrum due to strain relaxation or asymmetric structure of HAXPES by the Sn segregation was observed for the newly grown GeSn film of 6% Sn. A decrease in the broad peak intensity on the high binding energy side due to surface oxidation was also confirmed. Since the surface is more stabilized by Sb with lower interfacial free energy, it is expected that suppression of Sn segregation and uniform Sn concentration in depth direction are simultaneously achieved. The concentration distribution of Ge and Sb were confirmed by the RBS and SIMS, and it was revealed that the Sn concentration was uniform in the depth direction, and the composition of Sn and Sb was 6.6 at.% and 0.5 at.%, respectively. Hence, by combining newly developed MOCVD technique and synchrotron technique, it was confirmed that uniform GeSn thin layer with higher Sn composition was realized. Reference [1] S.Zaima, JJAP 52 (2013) 030001, [2] R.Cjhen et al., APL 99, (2011) 181125, [3] C. Thurmond et al., J.Chem.Phys. 25,(1956)799, [4] K.Suda et al., ECS J.SSST, 4 (2015) 152. [5] K.Usuda et al., MRS spring meeting, (2016), EP11.6.10. [6] X. Yang et al., IEEE Photon.Tech.Lett.12,(2000) 128. Figure 1

(Invited) High-Sn Concentration MOCVD-Grown Strained GeSn Thin Films Evaluated Using HAXPES and XRD Base on Synchrotron Technique

We demonstrate a GeSn growth method that uses new source gases to increase the Sn concentration of GeSn thin films, which are attracting attention as a next-generation semiconductor material for replacing for Si. Synchrotron radiation techniques are very useful for physical analysis of ultrathin films, particularly hard X-ray photoelectron spectroscopy, which can simultaneously analyze the outermost surface of the thin film and the bulk GeSn just underneath. As a result, we obtained results suggesting the growth of a high-quality GeSn thin film with suppression of surface Sn segregation and surface oxidation. Analysis of Sn concentration using a combination of Rutherford backscattering spectroscopy and secondary ion mass spectrometry revealed that the concentration of Sn was about 6.6 atom % and that the Sn content was uniform in the depth direction. These synchrotron techniques are expected to facilitate the preparation of high-quality, high-Sn GeSn thin films.

NRVS Studies of the Peroxide Shunt Intermediate in a Rieske Dioxygenase and Its Relation to the Native FeII O2 Reaction.

The Rieske dioxygenases are a major subclass of mononuclear nonheme iron enzymes that play an important role in bioremediation. Recently, a high-spin FeIII-(hydro)peroxy intermediate (BZDOp) has been trapped in the peroxide shunt reaction of benzoate 1,2-dioxygenase. Defining the structure of this intermediate is essential to understanding the reactivity of these enzymes. Nuclear resonance vibrational spectroscopy (NRVS) is a recently developed synchrotron technique that is ideal for obtaining vibrational, and thus structural, information on Fe sites, as it gives complete information on all vibrational normal modes containing Fe displacement. In this study, we present NRVS data on BZDOp and assign its structure using these data coupled to experimentally calibrated density functional theory calculations. From this NRVS structure, we define the mechanism for the peroxide shunt reaction. The relevance of the peroxide shunt to the native FeII/O2 reaction is evaluated. For the native FeII/O2 reaction, an FeIII-superoxo intermediate is found to react directly with substrate. This process, while uphill thermodynamically, is found to be driven by the highly favorable thermodynamics of proton-coupled electron transfer with an electron provided by the Rieske [2Fe-2S] center at a later step in the reaction. These results offer important insight into the relative reactivities of FeIII-superoxo and FeIII-hydroperoxo species in nonheme Fe biochemistry.

Monitoring microstructural evolution in-situ during cyclic deformation by high resolution reciprocal space mapping

The recently developed synchrotron technique High Resolution Reciprocal Space Mapping (HRRSM) is used to characterize the deformation structures evolving during cyclic deformation of commercially pure, polycrystalline aluminium AA1050. Insight into the structural reorganization within single grains is gained by in-situ monitoring of the microstructural evolution during cyclic deformation. By HRRSM, a large number of individual subgrains can be resolved within individual grains in the bulk of polycrystalline specimens and their fate, their individual orientation and elastic stresses, tracked during different loading regimes as tension and compression. With this technique, the evolution of dislocation structures in selected grains was followed during an individual load cycle.

Three-dimensional local residual stress and orientation gradients near graphite nodules in ductile cast iron

A synchrotron technique, differential aperture X-ray microscopy (DAXM), has been applied to characterize the microstructure and analyze the local mesoscale residual elastic strain fields around graphite nodules embedded in ferrite matrix grains in ductile cast iron. Compressive residual elastic strains are measured with a maximum strain of ∼6.5–8 × 10−4 near the graphite nodules extending into the matrix about 20 μm, where the elastic strain is near zero. The experimental data are compared with a strain gradient calculated by a finite element model, and good accord has been found but with a significant overprediction of the maximum strain. This is discussed in terms of stress relaxation during cooling or during storage by plastic deformation of the nodule, the matrix or both. Relaxation by plastic deformation of the ferrite is demonstrated by the formation of low energy dislocation cell structure also quantified by the DAXM technique.

Effect of atmospheric CO2 on surface segregation and phase formation in La0.6Sr0.4Co0.2Fe0.8O3−δ thin films

The effects of atmospheric CO2 on surface segregation and phase formation in La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF-6428) were investigated. (001)-oriented LSCF-6428 thin films were deposited on lattice matched (110)-oriented NdGaO3 (NGO) substrates by pulsed laser deposition (PLD). Using the synchrotron technique of total reflection X-ray fluorescence (TXRF), it was found that the kinetics of Sr surface segregation was enhanced when annealing at 800°C in a high-CO2 partial pressure, as compared to a similar anneal in a CO2-free atmosphere, with the oxygen partial pressure being constant in both cases. Hard X-ray photoelectron spectroscopy (HAXPES) measurements showed that the contribution of the surface carbonate to surface oxide phases increased significantly for the sample annealed in the high-CO2 atmosphere. Atomic force microscopy (AFM) studies showed enhanced surface phase formation during the high-CO2 partial pressure anneal. Density functional theory (DFT) calculations provide a thermodynamic basis for the enhanced kinetics of surface segregation in the presence of atmospheric CO2.

Properties of Ti3AlH6 and Ti3AlD6 systems at high pressure studied by synchrotron X-ray diffraction analysis

Compressibility of the Ti3AlH6 and Ti3AlD6 has been studied by X-ray diffraction method using advanced synchrotron technique up to 38GPa. Significantly higher values of bulk modulus have been revealed for the hydride and deuteride compounds as compared to the initial pure intermetallic compound. The consequences of this observation have been discussed in terms of ductility and strength of obtained materials. Possible explanation of the peculiarity in the equation of states for both compounds is proposed on the base of the difference in repulsion interactions of hydrogen and deuterium species in the metallic lattice. All advantages of the hydrogenation of titanium aluminum compound have been summarized.

Effect of Atmospheric Carbon Dioxide on Surface Segregation and Phase Formation in La0.6Sr0.4Co0.2Fe0.8O3-δThin Films

ABSTRACTThis study investigates Sr surface segregation behavior and phase formation in La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF), a commonly used cathode material for solid oxide fuel cells (SOFCs). (100)-oriented LSCF thin films were deposited on (110)-oriented NdGaO3(NGO) substrates by Pulsed Laser Deposition (PLD). The samples were annealed in atmospheres with various CO2partial pressures at 800°C. Using the synchrotron technique of Total Reflection X-ray Fluorescence (TXRF), surface segregation in these thin films were quantified. The morphological changes at the surface were examined by AFM studies. The kinetics and thermodynamics of the segregation are discussed.