Analysis of Performance Losses and Degradation Mechanism in Porous La2−X NiTiO6−δ:YSZ Electrodes

The electrode performance and degradation of 1:1 La_2−xNiTiO_6−δ:YSZ composites (x = 0, 0.2) has been investigated to evaluate their potential use as SOFC cathode materials by combining electrochemical impedance spectroscopy in symmetrical cell configuration under ambient air at 1173 K, XRD, electron microscopy and image processing studies. The polarisation resistance values increase notably, i.e., 0.035 and 0.058 Ωcm² h⁻¹ for x = 0 and 0.2 samples, respectively, after 300 h under these demanding conditions. Comparing the XRD patterns of the initial samples and after long-term exposure to high temperature, the perovskite structure is retained, although La₂Zr₂O₇ and NiO appear as secondary phases accompanied by peak broadening, suggesting amorphization or reduction of the crystalline domains. SEM and TEM studies confirm the ex-solution of NiO with time in both phases and also prove these phases are prone to disorder. From these results, degradation in La_2−xNiTiO_6−δ:YSZ electrodes is due to the formation of La₂Zr₂O₇ at the electrode–electrolyte interface and the ex-solution of NiO, which in turn results in the progressive structural amorphization of La₁₈NiTiO_6−δ phases. Both secondary phases constitute a non-conductive physical barrier that would hinder the ionic diffusion at the La_2−xNiTiO_6−δ:YSZ interface and oxygen access to surface active area.     

Effect of Sintering Process on Ionic Conductivity of Li7-xLa3Zr2-xNbxO12 (x = 0, 0.2, 0.4, 0.6) Solid Electrolytes

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) is considered as a promising solid electrolyte. Nb-doped LLZO ceramics exhibit significantly improved ion conductivity. However, how to prepare the Nb-doped LLZO ceramics in a simple and economical way, meanwhile to investigate the relationship between process conditions and properties in Li_7-xLa₃Zr_2-xNb_xO₁₂ ceramics, is particularly important. In this study, Li_7-xLa₃Zr_2-xNb_xO₁₂ (LLZN_xO, x = 0, 0.2, 0.4, 0.6) ceramics were prepared by conventional solid-state reaction. The effect of sintering process on the structure, microstructure, and ionic conductivity of LLZN_xO (x = 0, 0.2, 0.4, 0.6) ceramics was investigated. Due to the more contractive Nb-O bonds in LLZN_xO ceramics, the cubic structures are much easier to form and stabilize, which could induce the decreased preparation time. High-performance garnet LLZN_xO ceramics can be obtained by optimizing the sintering process with lower calcining temperature and shorter holding time. The garnet samples with x = 0.4 calcined at 850 °C for 10 h and sintered at 1250 °C for 4 h exhibit the highest ionic conductivity of 3.86 × 10⁻⁴ S·cm⁻¹ at room temperature and an activation energy of 0.32 eV, which can be correlated to the highest relative density of 96.1%, and good crystallinity of the grains.     

The Vital Role of La2O3 on the La2O3-CaO-B2O3-SiO2 Glass System for Shielding Some Common Gamma Ray Radioactive Sources

The role La₂O₃ on the radiation shielding properties of La₂O₃-CaO-B₂O₃-SiO₂ glass systems was investigated. The energies were selected between 0.284 and 1.275 MeV and Phy-X software was used for the calculations. BLa10 glass had the least linear attenuation coefficient (LAC) at all the tested energies, while BLa30 had the greatest, which indicated that increasing the content of La₂O₃ in the BLa-X glasses enhances the shielding performance of these glasses. The mass attenuation coefficient (MAC) of BLa15 decreases from 0.150 cm²/g to 0.054 cm²/g at energies of 0.284 MeV and 1.275 MeV, respectively, while the MAC of BLa25 decreases from 0.164 cm²/g to 0.053 cm²/g for the same energies, respectively. At all energies, the effective atomic number (Z_eff) values follow the trend BLa10 < BLa15 < BLa20 < BLa25 < BLa30. The half value thickness (HVL) of the BLa-X glass shields were also investigated. The minimum HVL values are found at 0.284 MeV. The HVL results demonstrated that BLa30 is the most space-efficient shield. The tenth value layer (TVL) results demonstrated that the glasses are more effective attenuators at lower energies, while decreasing in ability at greater energies. These mean free path results proved that increasing the density of the glasses, by increasing the amount of La₂O₃ content, lowers MFP, and increases attenuation, which means that BLa30, the glass with the greatest density, absorbs the most amount of radiation.     

Spray Flame Synthesis (SFS) of Lithium Lanthanum Zirconate (LLZO) Solid Electrolyte

A spray-flame reaction step followed by a short 1-h sintering step under O₂ atmosphere was used to synthesize nanocrystalline cubic Al-doped Li₇La₃Zr₂O₁₂ (LLZO). The as-synthesized nanoparticles from spray-flame synthesis consisted of the crystalline La₂Zr₂O₇ (LZO) pyrochlore phase while Li was present on the nanoparticles’ surface as amorphous carbonate. However, a short annealing step was sufficient to obtain phase pure cubic LLZO. To investigate whether the initial mixing of all cations is mandatory for synthesizing nanoparticulate cubic LLZO, we also synthesized Li free LZO and subsequently added different solid Li precursors before the annealing step. The resulting materials were all tetragonal LLZO (I4₁/acd) instead of the intended cubic phase, suggesting that an intimate intermixing of the Li precursor during the spray-flame synthesis is mandatory to form a nanoscale product. Based on these results, we propose a model to describe the spray-flame based synthesis process, considering the precipitation of LZO and the subsequent condensation of lithium carbonate on the particles’ surface.     

Vectorial proton transfer coupled to reduction of O2 and NO by a heme-copper oxidase

The heme-copper oxidase (HCuO) superfamily consists of integral membrane proteins that catalyze the reduction of either oxygen or nitric oxide. The HCuOs that reduce O₂ to H₂O couple this reaction to the generation of a transmembrane proton gradient by using electrons and protons from opposite sides of the membrane and by pumping protons from inside the cell or organelle to the outside. The bacterial NO-reductases (NOR) reduce NO to N₂O (2NO + 2e⁻ + 2H⁺ → N₂O + H₂O), a reaction as exergonic as that with O₂. Yet, in NOR both electrons and protons are taken from the outside periplasmic solution, thus not conserving the free energy available. The cbb₃-type HCuOs catalyze reduction of both O₂ and NO. Here, we have investigated energy conservation in the Rhodobacter sphaeroides cbb₃ oxidase during reduction of either O₂ or NO. Whereas O₂ reduction is coupled to buildup of a substantial electrochemical gradient across the membrane, NO reduction is not. This means that although the cbb₃ oxidase has all of the structural elements for uptake of substrate protons from the inside, as well as for proton pumping, during NO reduction no pumping occurs and we suggest a scenario where substrate protons are derived from the outside solution. This would occur by a reversal of the proton pathway normally used for release of pumped protons. The consequences of our results for the general pumping mechanism in all HCuOs are discussed.     

Study on Structure and Properties of La2O3-Doped Basaltic Glasses for Immobilizing Simulated Lanthanides

The La₂O₃-doped basaltic glass simulated high-level waste form (HLW) was prepared by the solid-state melt method. The simulated waste La₂O₃ maximum loading and the doping effect on structure, thermal stability, leaching behavior, density, and hardness of basaltic glasses were studied. XRD and SEM results show that the simulated waste loading of La₂O₃ in basaltic glass can be up to ~46 wt.%, and apatite (CaLa₄(SiO₄)₃O) precipitates when the content of La₂O₃ reaches 56 wt.%. Raman results indicate that the addition of La₂O₃ breaks the Si–O–Si bond of large-membered and four-membered, but the number of A1³⁺ involved in the formation of the network increase. Low content of La₂O₃ can help to repair the glass network, but it destroys the network as above 26 wt.%. DSC results show the thermal stability of simulated waste forms first increases and then decreases with the increase of La₂O₃ content. With the increase of La₂O₃ content, the density of the simulated waste form increases, and the hardness decreases. The leaching chemical stability of samples was evaluated by the ASTM Product Consistency Test (PCT) Method, which show that all the samples have good chemical stability. The leaching rates of La and Fe are three orders of magnitude lower than those of the other elements. Among them, L36 has the best comprehensive leaching performance.     

Optically Active TiO2:Er Thin Films Deposited by Magnetron Sputtering

Titanium dioxide photoanodes for hydrogen generation suffer from a profound mismatch between the optical absorption of TiO₂ and the solar spectrum. To solve the problem of low solar-to-chemical efficiency, optically active materials are proposed. In this work, TiO₂ thin films containing erbium were deposited by radio frequency RF magnetron sputtering under ultrahigh vacuum conditions UHV. Morphology, structural, optical and electronic properties were studied. TiO₂:Er thin films are homogenous, with uniform distribution of Er ions and high transparency over the visible VIS range of the light spectrum. However, a profound 0.4 eV blue shift of the fundamental absorption edge with respect to undoped TiO₂ was observed, which can be attributed either to the size effect due to amorphization of TiO₂ host or to the onset of precipitation of Er₂Ti₂O₇ nanocrystals. Near-infrared NIR to VIS up-conversion is demonstrated upon excitation at 980 nm, while strong green photoluminescence at 525 and 550 nm occurs upon photon absorption at 488 nm.     

Linking the Electrical Conductivity and Non-Stoichiometry of Thin Film Ce1−xZrxO2−δ by a Resonant Nanobalance Approach

Bulk ceria-zirconia solid solutions (Ce_1−xZr_xO_2−δ, CZO) are highly suited for application as oxygen storage materials in automotive three-way catalytic converters (TWC) due to the high levels of achievable oxygen non-stoichiometry δ. In thin film CZO, the oxygen storage properties are expected to be further enhanced. The present study addresses this aspect. CZO thin films with 0 ≤ x ≤ 1 were investigated. A unique nano-thermogravimetric method for thin films that is based on the resonant nanobalance approach for high-temperature characterization of oxygen non-stoichiometry in CZO was implemented. The high-temperature electrical conductivity and the non-stoichiometry δ of CZO were measured under oxygen partial pressures pO₂ in the range of 10⁻²⁴–0.2 bar. Markedly enhanced reducibility and electronic conductivity of CeO₂-ZrO₂ as compared to CeO_2−δ and ZrO₂ were observed. A comparison of temperature- and pO₂-dependences of the non-stoichiometry of thin films with literature data for bulk Ce_1−xZr_xO_2−δ shows enhanced reducibility in the former. The maximum conductivity was found for Ce_0.8Zr_0.2O_2−δ, whereas Ce_0.5Zr_0.5O_2-δ showed the highest non-stoichiometry, yielding δ = 0.16 at 900 °C and pO₂ of 10⁻¹⁴ bar. The defect interactions in Ce_1−xZr_xO_2−δ are analyzed in the framework of defect models for ceria and zirconia.     

New Insights into the Crystal Chemistry of Elpidite,Na2Zr[Si6O15]·3H2O and (Na1+YCax□1−X−Y)Σ=2Zr[Si6O15]·(3−X)H2O,and Ab Initio Modeling of IR Spectra

Elpidite belongs to a special group of microporous zirconosilicates, which are of great interest due to their capability to uptake various molecules and ions, e.g., some radioactive species, in their structural voids. The results of a combined electron probe microanalysis and single-crystal X-ray diffraction study of the crystals of elpidite from Burpala (Russia) and Khan-Bogdo (Mongolia) deposits are reported. Some differences in the chemical compositions are observed and substitution at several structural positions within the structure of the compounds are noted. Based on the obtained results, a detailed crystal–chemical characterization of the elpidites under study was carried out. Three different structure models of elpidite were simulated: Na₂ZrSi₆O₁₅·3H₂O (related to the structure of Russian elpidite), partly Ca-replaced Na_1.5Ca_0.25ZrSi₆O₁₅·2.75H₂O (close to elpidite from Mongolia), and a hypothetical CaZrSi₆O₁₅·2H₂O. The vibration spectra of the models were obtained and compared with the experimental one, taken from the literature. The strong influence of water molecule vibrations on the shape of IR spectra of studied structural models of elpidite is discussed in the paper.     

Novel Microwave-Assisted Method of Y2Ti2O7 Powder Synthesis

In the paper, a novel technique for highly dispersed pyrochlore Y₂Ti₂O₇ is proposed. The experimental results proved that the application of microwave irradiation at a certain stage of calcination allowed synthesizing of Y₂Ti₂O₇ in much shorter time, which ensured substantial energy savings. An increase up to 98 wt.% in the content of the preferred phase with a pyrochlore-type structure Y₂Ti₂O₇ was obtained after 25 h of yttrium and titanium oxides calcination at a relatively low temperature of 1150 °C, while the microwave-supported process took only 9 h and provided 99 wt.% of pyrochlore. The proposed technology is suitable for industrial applications, enabling the fabrication of large industrial amounts of pyrochlore without solvent chemistry and high-energy mills. It reduced the cost of both equipment and energy and made the process more environmentally friendly. The particle size and morphology did not change significantly; therefore, the microwave-assisted method can fully replace the traditional one.     

Impact of Zr-Doped Bi2O3 Radiopacifier by Spray Pyrolysis on Mineral Trioxide Aggregate

Mineral trioxide aggregates (MTA) have been developed as a dental root repair material for a range of endodontics procedures. They contain a small amount of bismuth oxide (Bi₂O₃) as a radiopacifier to differentiate adjacent bone tissue on radiographs for endodontic surgery. However, the addition of Bi₂O₃ to MTA will increase porosity and lead to the deterioration of MTA’s mechanical properties. Besides, Bi₂O₃ can also increase the setting time of MTA. To improve upon the undesirable effects caused by Bi₂O₃ additives, we used zirconium ions (Zr) to substitute the bismuth ions (Bi) in the Bi₂O₃ compound. Here we demonstrate a new composition of Zr-doped Bi₂O₃ using spray pyrolysis, a technique for producing fine solid particles. The results showed that Zr ions were doped into the Bi₂O₃ compound, resulting in the phase of Bi_7.38Zr_0.62O_12.31. The results of materials analysis showed Bi₂O₃ with 15 mol % of Zr doping increased its radiopacity (5.16 ± 0.2 mm Al) and mechanical strength, compared to Bi₂O₃ and other ratios of Zr-doped Bi₂O₃. To our knowledge, this is the first study of fabrication and analysis of Zr-doped Bi₂O₃ radiopacifiers through the spray pyrolysis procedure. The study reveals that spray pyrolysis can be a new technique for preparing Zr-doped Bi₂O₃ radiopacifiers for future dental applications.     

Structural Features of Y2O2SO4 via DFT Calculations of Electronic and Vibrational Properties

The traditional way for determination of molecular groups structure in crystals is the X-Ray diffraction analysis and it is based on an estimation of the interatomic distances. Here, we report the analysis of structural units in Y₂O₂SO₄ using density functional theory calculations of electronic properties, lattice dynamics and experimental vibrational spectroscopy. The Y₂O₂SO₄ powder was successfully synthesized by decomposition of Y₂(SO₄)₃ at high temperature. According to the electronic band structure calculations, yttrium oxysulfate is a dielectric material. The difference between the oxygen–sulfur and oxygen–yttrium bond nature in Y₂O₂OS₄ was shown based on partial density of states calculations. Vibrational modes of sulfur ions and [Y₂O₂²⁺] chains were obtained theoretically and corresponding spectral lines observed in experimental Infrared and Raman spectra.     

Radiation Tolerance and Charge Trapping Enhancement of ALD HfO2/Al2O3 Nanolaminated Dielectrics

High-k dielectric stacks are regarded as a promising information storage media in the Charge Trapping Non-Volatile Memories, which are the most viable alternative to the standard floating gate memory technology. The implementation of high-k materials in real devices requires (among the other investigations) estimation of their radiation hardness. Here we report the effect of gamma radiation (⁶⁰Co source, doses of 10 and 10 kGy) on dielectric properties, memory windows, leakage currents and retention characteristics of nanolaminated HfO₂/Al₂O₃ stacks obtained by atomic layer deposition and its relationship with post-deposition annealing in oxygen and nitrogen ambient. The results reveal that depending on the dose, either increase or reduction of all kinds of electrically active defects (i.e., initial oxide charge, fast and slow interface states) can be observed. Radiation generates oxide charges with a different sign in O₂ and N₂ annealed stacks. The results clearly demonstrate a substantial increase in memory windows of the as-grown and oxygen treated stacks resulting from enhancement of the electron trapping. The leakage currents and the retention times of O₂ annealed stacks are not deteriorated by irradiation, hence these stacks have high radiation tolerance.     

Experimental Investigation of Radiation Shielding Competence of Bi2O3-CaO-K2O-Na2O-P2O5 Glass Systems

The gamma-ray shielding features of Bi₂O₃-CaO-K₂O-Na₂O-P₂O₅ glass systems were experimentally reported. The mass attenuation coefficient (MAC) for the fabricated glasses was experimentally measured at seven energy values (between 0.0595 and 1.33 MeV). The compatibility between the practical and theoretical results shows the accuracy of the results obtained in the laboratory for determining the MAC of the prepared samples. The mass and linear attenuation coefficients (MACs) increase with the addition of Bi₂O₃ and A4 glass possesses the highest MAC and LAC. A downward trend in the linear attenuation coefficient (LAC) with increasing the energy from 0.0595 to 1.33 MeV is found. The highest LAC is found at 1.33 MeV (in the range of 0.092–0.143 cm⁻¹). The effective atomic number (Z_eff) follows the order B1 > A1 > A2 > A3 > A4. This order emphasizes that increasing the content of Bi₂O₃ has a positive effect on the photon shielding proficiencies owing to the higher density of Bi₂O₃ compared with Na₂O. The half value layer (HVL) is also determined and the HVL for the tested glasses is computed between 0.106 and 0.958 cm at 0.0595 MeV. The glass with 10 mol% of Bi₂O₃ has lower HVL than the glasses with 0, 2.5, 5, and 7.5 mol% of Bi₂O₃. So, the A4 glass needs a smaller thickness than the other glasses to shield the same radiation. As a result of the reported shielding parameters, inserting B₂O₃ provides lower values of these three parameters, which in turn leads to the development of superior photons shields.     

Network topology for the formation of solvated electrons in binary CaO–Al2O3 composition glasses

Glass formation in the CaO–Al₂O₃ system represents an important phenomenon because it does not contain typical network-forming cations. We have produced structural models of CaO–Al₂O₃ glasses using combined density functional theory–reverse Monte Carlo simulations and obtained structures that reproduce experiments (X-ray and neutron diffraction, extended X-ray absorption fine structure) and result in cohesive energies close to the crystalline ground states. The O–Ca and O–Al coordination numbers are similar in the eutectic 64 mol % CaO (64CaO) glass [comparable to 12CaO·7Al₂O₃ (C12A7)], and the glass structure comprises a topologically disordered cage network with large-sized rings. This topologically disordered network is the signature of the high glass-forming ability of 64CaO glass and high viscosity in the melt. Analysis of the electronic structure reveals that the atomic charges for Al are comparable to those for Ca, and the bond strength of Al–O is stronger than that of Ca–O, indicating that oxygen is more weakly bound by cations in CaO-rich glass. The analysis shows that the lowest unoccupied molecular orbitals occurs in cavity sites, suggesting that the C12A7 electride glass [Kim SW, Shimoyama T, Hosono H (2011) Science 333(6038):71–74] synthesized from a strongly reduced high-temperature melt can host solvated electrons and bipolarons. Calculations of 64CaO glass structures with few subtracted oxygen atoms (additional electrons) confirm this observation. The comparable atomic charges and coordination of the cations promote more efficient elemental mixing, and this is the origin of the extended cage structure and hosted solvated (trapped) electrons in the C12A7 glass.     

Delocalization of Electrons in Strong Insulators at High Dynamic Pressures

Systematics of material responses to shock flows at high dynamic pressures are discussed. Dissipation in shock flows drives structural and electronic transitions or crossovers, such as used to synthesize metallic liquid hydrogen and most probably Al₂O₃ metallic glass. The term “metal” here means electrical conduction in a degenerate system, which occurs by band overlap in degenerate condensed matter, rather than by thermal ionization in a non-degenerate plasma. Since H₂ and probably disordered Al₂O₃ become poor metals with minimum metallic conductivity (MMC) virtually all insulators with intermediate strengths do so as well under dynamic compression. That is, the magnitude of strength determines the split between thermal energy and disorder, which determines material response. These crossovers occur via a transition from insulators with electrons localized in chemical bonds to poor metals with electron energy bands. For example, radial extents of outermost electrons of Al and O atoms are 7 a₀ and 4 a₀, respectively, much greater than 1.7 a₀ needed for onset of hybridization at 300 GPa. All such insulators are Mott insulators, provided the term “correlated electrons” includes chemical bonds.     

Ti Addition Effect on the Grain Structure Evolution and Thermoelectric Transport Properties of Hf0.5Zr0.5NiSn0.98Sb0.02 Half-Heusler Alloy

Compositional tuning is one of the important approaches to enhance the electronic and thermal transport properties of thermoelectric materials since it can generate point defects as well as control the phase evolution behavior. Herein, we investigated the Ti addition effect on the grain growth during melt spinning and thermoelectric transport properties of Hf_0.5Zr_0.5NiSn_0.98Sb_0.02 half-Heusler compound. The characteristic grain size of melt-spun ribbons was reduced by Ti addition, and very low lattice thermal conductivity lower than 0.27 W m⁻¹ K⁻¹ was obtained within the whole measured temperature range (300–800 K) due to the intensified point defect (substituted Ti) and grain boundary (reduced grain size) phonon scattering. Due to this synergetic effect on the thermal transport properties, a maximum thermoelectric figure of merit, zT, of 0.47 was obtained at 800 K in (Hf_0.5Zr_0.5)_0.8Ti_0.2NiSn_0.98Sb_0.02.     

A kinetic and thermodynamic understanding of O2 tolerance in [NiFe]-hydrogenases

In biology, rapid oxidation and evolution of H₂ is catalyzed by metalloenzymes known as hydrogenases. These enzymes have unusual active sites, consisting of iron complexed by carbonyl, cyanide, and thiolate ligands, often together with nickel, and are typically inhibited or irreversibly damaged by O₂. The Knallgas bacterium Ralstonia eutropha H16 (Re) uses H₂ as an energy source with O₂ as a terminal electron acceptor, and its membrane-bound uptake [NiFe]-hydrogenase (MBH) is an important example of an “O₂-tolerant” hydrogenase. The mechanism of O₂ tolerance of Re MBH has been probed by measuring H₂ oxidation activity in the presence of O₂ over a range of potential, pH and temperature, and comparing with the same dependencies for individual processes involved in the attack by O₂ and subsequent reactivation of the active site. Most significantly, O₂ tolerance increases with increasing temperature and decreasing potentials. These trends correlate with the trends observed for reactivation kinetics but not for H₂ affinity or the kinetics of O₂ attack. Clearly, the rate of recovery is a crucial factor. We present a kinetic and thermodynamic model to account for O₂ tolerance in Re MBH that may be more widely applied to other [NiFe]-hydrogenases.     

High-energy resolution X-ray absorption and emission spectroscopy reveals insight into unique selectivity of La-based nanoparticles for CO2

The lanthanum-based materials, due to their layered structure and f-electron configuration, are relevant for electrochemical application. Particularly, La₂O₂CO₃ shows a prominent chemoresistive response to CO₂. However, surprisingly less is known about its atomic and electronic structure and electrochemically significant sites and therefore, its structure–functions relationships have yet to be established. Here we determine the position of the different constituents within the unit cell of monoclinic La₂O₂CO₃ and use this information to interpret in situ high-energy resolution fluorescence-detected (HERFD) X-ray absorption near-edge structure (XANES) and valence-to-core X-ray emission spectroscopy (vtc XES). Compared with La(OH)₃ or previously known hexagonal La₂O₂CO₃ structures, La in the monoclinic unit cell has a much lower number of neighboring oxygen atoms, which is manifested in the whiteline broadening in XANES spectra. Such a superior sensitivity to subtle changes is given by HERFD method, which is essential for in situ studying of the interaction with CO₂. Here, we study La₂O₂CO₃-based sensors in real operando conditions at 250 °C in the presence of oxygen and water vapors. We identify that the distribution of unoccupied La d-states and occupied O p- and La d-states changes during CO₂ chemoresistive sensing of La₂O₂CO₃. The correlation between these spectroscopic findings with electrical resistance measurements leads to a more comprehensive understanding of the selective adsorption at La site and may enable the design of new materials for CO₂ electrochemical applications.CO₂ has become a challenge for our society and we have to develop new materials for its photo/electrocatalysis, chemoresistive sensing, and storage (1–8). Particularly, for the variety of electrochemical applications the selective interaction of CO₂ and charge transfer with solids is in the foreground. At the same time, the interaction of CO₂ with solids in the electrochemical cell or sensing device is rather complex, thus it remains challenging to experimentally identify the key elements determining their selectivity and efficiency. X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) provide complementary information on the electronic structure of materials (9, 10) and on the orbitals participating in the interaction with absorbing molecules (11). High-energy resolution fluorescence-detected (HERFD) XAS probes unoccupied states with a spectral resolution higher than regular XAS. Furthermore, with the same experimental setup XES can be measured, which allows one to probe the occupied states within the valence band (12). In situ HERFD XAS or XES experiments have been previously carried out to study the catalytic reaction at the surface of noble metals (11, 13–16), zeolites (17), and metal organic frameworks (18). Thus far, no such in situ experiments have been performed to directly track the changes of the electronic structure of a solid and its electrochemical activity toward CO₂. The rare-earth–based materials like perovskites and oxycarbonates, owing to their unique f-electron configuration of Ln (Ln = rare earth) and layered crystal structure, emerge as the most interesting for future photo- and electrochemical applications (3–8). Among rare-earth oxycarbonates (19, 20), particularly lanthanum strongly responds to CO₂ and shows up to 16-fold conductivity changes, not seen before for any metal oxides (21). This is very surprising because a direct injection of an electron into CO₂ molecule requires the activation energy of nearly 2 eV (22). To assess the origins of the unique CO₂ sensitivity of rare-earth oxycarbonate, it is essential to study in situ the interplay between the changes of the electronic structure of La-based nanoparticles upon CO₂ adsorption and changes of the macroscopic conductivity of a device.Here, to elucidate the underlying mechanism we first determine the structure and atomic positions of the lanthanum oxycarbonate. Using HERFD XAS and valence-to-core (vtc) XES results, we gain information about the electronic structure and band gap. Moreover, we combine in situ HERFD XAS and XES measurements with sensing performance tests to obtain the structure–function relationship. Finally, with all of the obtained information we discuss a mechanism of CO₂ adsorption on the La₂O₂CO₃ surface.     

Tension-Tension Fatigue Behavior of High-Toughness Zr61Ti2Cu25Al12 Bulk Metallic Glass

Bulk metallic glasses have application potential in engineering structures due to their exceptional strength and fracture toughness. Their fatigue resistance is very important for the application as well. We report the tension-tension fatigue damage behavior of a Zr₆₁Ti₂Cu₂₅Al₁₂ bulk metallic glass, which has the highest fracture toughness among BMGs. The Zr₆₁Ti₂Cu₂₅Al₁₂ glass exhibits a tension-tension fatigue endurance limit of 195 MPa, which is higher than that of high-toughness steels. The fracture morphology of the specimens depends on the applied stress amplitude. We found flocks of shear bands, which were perpendicular to the loading direction, on the surface of the fatigue test specimens with stress amplitude higher than the fatigue limit of the glass. The fatigue cracking of the glass initiated from a shear band in a shear band flock. Our work demonstrated that the Zr₆₁Ti₂Cu₂₅Al₁₂ glass is a competitive structural material and shed light on improving the fatigue resistance of bulk metallic glasses.