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For extraction of metallic lanthanum from molten NaCl-CsCl-LaCl3 solutions, the electrochemical reduction of La(III) ions on inert Mo and liquid Ga electrodes were explored. Transient electrochemical techniques have been used to explore the reduction mechanism, transport parameters and thermodynamics properties. The obtained results indicate that the electrochemical reaction of La(III) + 3ē → La on inert electrode is a single-stage irreversible process, which controlled by the charge transfer rate. Simultaneously, the diffusion coefficient of [LaCl6] 3− complex ions was obtained at different temperatures. The apparent standard potentials of La3+/La couple and La-Ga alloy vs the temperature were determined. The base thermodynamic properties of lanthanum compounds were calculated. Furthermore, the potentiostatic method of electrolysis was used for the synthesis of La-Ga alloys. [ABSTRACT FROM AUTHOR]

Highly conducting and transparent thin films of LaxBa1 − xSnO3 (x = 0, 0.01 and 0.05) were grown on quartz substrates via pulsed laser deposition. Conductivity increases in orders of magnitude upon vacuum annealing of the as–deposited films. This is attributed to the significant enhancement in carrier concentration due to the increased oxygen vacancy defects (V). Enhanced carrier concentration improves the metallicity in the films at room temperature. Metal to semiconductor transition (MST) is observed in the films with ne 1019 cm−3 at low temperatures. The MST shifts towards absolute zero temperature as the carrier concentration in the film increases. Low–temperature resistivity analysis suggests that the charge transport is mainly governed by strong electron–electron interaction. UV–Vis spectroscopy confirms a 60%–80% transmittance in the visible range (400–800 nm) for all the films. Due to the large change in carrier concentration, Burstein Moss (BM) shift is observed, and the bandgap ranges between 3.65–3.98 eV. The effective mass of electron and refractive index estimated from the BM shift and transmittance are found to be 0.6 me and 2, respectively. [ABSTRACT FROM AUTHOR]

Factors governing the change of the surface composition and the degradation of transport properties of La0.6Sr0.4Co0.2Fe0.8O3-d (LSCF) under low concentration sulfur-contained air (0.01 ppm) were examined as functions of water vapor pressure (p(H2O)) and oxygen partial pressure (p(O2)). Bulk LSCF samples were heat-treated at 973 K in dry or wet air containing SO2 and more enhanced SrSO4 formation/growth was observed under wet compared to dry air. When the p(O2) was changed from 0.21 to 0.01 bar, the SrSO4 precipitates became smaller in size and higher in number, indicating that the p(H2O) and the p(O2) have different effects on secondary phase formation. Detailed analysis of the surface composition indicates the presence of CoFe2O4 in the vicinity of the SrSO4 particle, suggesting the Sr and Co depletion in the subsurface region. Based on the analysis, the water vapor affects the secondary phase growth due to the possibility of additional reaction pathways that may enhance the growth rate. This behavior is correlated with the logarithmic surface oxygen exchange coefficient, log k*, that was observed to decrease monotonically within 20 h of annealing time but its degradation was found to be faster under wet air, in accordance with Sr and Co depletion rate. [ABSTRACT FROM AUTHOR]

The present studywas designed to synthesize lanthanum doped feathers-typeZnOnano-flower (feathers-type La3+-ZnO nano-flower), that are specified via Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). To simultaneously determine codeine and diclofenac using feather-type La3+-ZnO nano-flower modified carbon paste electrode (La3+-ZnO/CPE), an original cost-efficient and simple methodology is presented. Evidently, La3+-ZnO/CPE proved to be a prospective, stable, sensitive and chemically reliable electrochemical sensor to determine diclofenac and codeine simultaneously with no intervention or overlapping of voltammetric peaks or signals. Codeine electroanalytical sensing was examined via La3+-ZnO/CPE across an extensive concentration range at a relatively low detection limit of 0.01µM, (3S/N). La3+-ZnO/CPE of nanoscale feathers-type La3+-ZnO structure displays favorable practicality in analytical terms to accurately and simultaneously determine diclofenac and codeine within real specimens with exceptional recoveries. The outcomes prove exceptional La3+-ZnO/CPE performance in regard to facile, reliability and sensing capabilities which may favorably decrease the relevant processing expenses for routine analysis and scalable production. [ABSTRACT FROM AUTHOR]

Composite, Solid-Oxide-Fuel-Cell (SOFC) electrodes of La0.8Sr0.2FeO3 (LSF) and yttria-stabilized zirconia (YSZ) were prepared by infiltration methods and then modified by Atomic Layer Deposition (ALD) of ZrO2, La2O3, Fe2O3, or La2O3-Fe2O3codeposited films of different thicknesses to determine the effect of surface composition on cathode performance. Film growth rates for ALD performed using vacuum procedures at 573 K for Fe2O3 and 523 K for ZrO2 and La2O3 were determined to be 0.024 nm ZrO2/cycle, 0.019 nm La2O3/cycle, and 0.018 nm Fe2O3/cycle. For ZrO2 and Fe2O3, impedance spectra on symmetric cells at 873 K indicated that polarization resistances increased with coverage in a manner suggesting simple blocking of O2 adsorption sites. With La2O3, the polarization resistance decreased with small numbers of ALD cycles before again increasing at higher coverages. When La2O3 and Fe2O3 were co-deposited, the polarization resistances remained low at high film coverages, implying that O2 adsorption sites were formed on the co-deposited films. The implications of these results for future SOFC electrode development are discussed. [ABSTRACT FROM AUTHOR]

This work presents an electrochemical study of La(III) in the LiCl-KCl-LaCl3 melt on a liquid gallium electrode. The reduction of the La(III) on a liquid gallium starts at -1.13 V (vs. Ag/AgCl) and is a one step process with three electrons transferred. The activities, activity coefficients and solubilities of La in La-Ga alloys were calculated by open circuit potential technique at the temperature range of 673 to 823 K. Moreover, galvanodynamic methods was also applied on a W electrode to evaluate the apparent standard potential of La(III)/La couple, the Gibbs free energy for the formation of LaCl3 and the activity coefficient of La(III) in the LiCl-KCl-LaCl3 melt. The co-reductive cyclic voltammograms of La(III) and Ga(III) present several redox couples which correspond to the formation and dissolution of different La-Ga intermetallic compounds. Finally, potentiostatic electrolysis was employed to deposit La on a liquid Ga electrode and the intermetallic compound LaGa6 was identified by Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM-EDS) and X-ray diffraction (XRD) characterizations. [ABSTRACT FROM AUTHOR]

The design of electrolyte systems suitable for room-temperature electrochemical extraction of Li, Mg, Al, Ti, rare earth elements, and other active metals from their salts or oxides has long been a scientific challenge. Herein, we report an exceptional organic solvent (1,3-dimethyl-2-imidazolidinone) supported by LiNO3 with properties superior to those of conventional ionic liquids and show that it is well suited for room-temperature potentiostatic deposition of La coatings from LaCl3 on high-purity Al substrates. Thus, this work paves the way to cost-effective La extraction and presents an innovative approach to the selection of electrolyte systems used for electrodeposition of active metals. [ABSTRACT FROM AUTHOR]

Doped lanthanum polyphosphate (LaP3O9) exhibits relatively high proton conductivity. For the practical applications such as the electrolyte of fuel cells, however, its conductivity must be improved by 2 orders of magnitude. Protons are introduced into matrix by lower-valent cation doping, and proton conductivity depends on dopant species. To date, LaP3O9 has been doped with only Ca, Sr and Ba. In this work, we tried to dope LaP3O9 with Na+, K+, Mg2+ and Pb2+, as the new dopant species, due to their close ionic radii to La3+. Among them, only Pb could substitute for La at a comparable concentration to those of alkaline earth metals and its highest doping level was 6.4 mol% (Doping level is defined as the concentration ratio of dopant (M) to host cation (La) site in matrix (≡M/(La + M) x 100 (mol%))). Though Pb can exist as either divalent or tetravalent state, Pb in LaP3O9 was identified to be divalent state by XPS analysis. Proton conduction was demonstrated by H/D isotope effect. The electrical conductivity of Pb-doped LaP3O9 increased with Pb-doping level, owing to the increase in proton concentration. The conductivity of 4.5 mol% Pb-doped LaP3O9 was about one order of magnitude lower than that of 7.9 mol% Sr-doped LaP3O9. [ABSTRACT FROM AUTHOR]

Sr-doped lanthanum manganite (LSM) is a widely used cathode material in solid oxide fuel cells (SOFC). Despite being a poor ion conductor, LSM electrodes can reduce oxygen via two pathways: a "3PB surface path" which includes surface diffusion of oxygen species and oxide ion incorporation at the three phase boundary (3PB), and a "bulk path" based on oxygen diffusion in LSM. In this work, the kinetics of both paths and their dependence on temperature and electrode geometry is investigated by impedance spectroscopy on micropatterned LSM thin film electrodes. Differently shaped and sized macroscopic and microscopic LSM electrodes as well as LSM electrodes with oxygen blocking Pt capping layers are employed to identify two parallel reaction pathways of oxygen reduction. On circular microelectrodes the 3PB surface path carries most of the current in the lower temperature region (below ca. 700°C), while at high temperatures (above ca. 700°C) the bulk path is dominating. The significance of each reduction path also depends on the microstructure of the columnar LSM films which can be changed by varying pulsed laser deposition (PLD) parameters or by annealing. Moreover, relevance of a pseudo-3PB path across edges of the LSM electrodes is discussed. [ABSTRACT FROM AUTHOR]

Improved electrochemical performance of strontium-doped lanthanum manganite (LSM)/scandia-stabilized zirconia (ScSZ) composite cathodes for solid oxide fuel cells was accomplished by using the powder slurry impregnation (PSI) method where a prefabricated thin porous ScSZ electrolyte layer is impregnated with LSM/ScSZ powder mixture in slurry. The PSI method enabled control of the electrolyte surface roughness, resulting in a decreased electrode polarization resistance despite a tendency of the ohmic resistance to increase due to the added porous ScSZ electrolyte layer. Resistance separation by electrochemical impedance spectroscopy with an equivalent circuit model (ECM) revealed that the proposed composite cathodes exhibited a significant reduction in the oxygen reduction reaction (ORR) resistance at the triple-phase boundary (TPB). Optimization of the electrolyte surface structure is therefore critical so as not to offset the improvement in the ORR resistance. Furthermore, besides the ECM used to separate the resistances, two ECMs that represent the microstructure of actual composite electrodes were evaluated to clarify the electrode structural factors determining the measured impedance spectra. The analysis revealed that impedance response is influenced by the area ratio of the double-phase boundary to the TPB, although cathode performance is mainly determined by the TPB area and the ionic conduction resistance within composite electrodes. [ABSTRACT FROM AUTHOR]

Oxygen incorporation via the three-phase boundaries (3PBs) contributes significantly to the total oxygen reduction reaction on the composite consisting of La0.6Sr0.4Co0.2Fe0.8O3-d (LSCF) and samaria doped ceria (SDC). This work reveals that the reaction rate at the LSCF-SDC-gas 3PBs is affected by the samaria content and reaches the highest value with Sm0.2Ce0.8O2-d. When the incorporation step, where oxygen species on the surface combines to the oxygen vacancy from SDC, limits the total reaction, the rate can be related directly to SDC conductivity. The rate increases with the conductivity, demonstrating that the incorporation step dominates the total reaction which basically consists of three basic steps: the oxygen molecular adsorption, the dissociation, and the incorporation. In addition, the 3PB contribution is notably affected by the samaria content and increases with the conductivity. The reaction via 3PB contributes more than 60% of the total oxygen incorporated to the LSCF-Sm0.2Ce0.8O2-d composite. [ABSTRACT FROM AUTHOR]

Ni-La electrocatalytic systems have been synthesized via spray pyrolysis and studied for the electrooxidation of hydrazine hydrate in alkaline media. Characterization of phase compositions, crystal structures, morphologies, and surface compositions of the electrocatalysts performed via XRD, SEM, HRTEM, and XPS in combination with in situ IRRAS spectroelectrochemistry permitted the further understanding of the high electrochemical activity obtained from Ni-La (lanthanum hydroxide) catalytic systems. Ni0.90La0.10 and Nio.95Lao.05 have been identified as highly active electrocatalysts for the oxidation of hydrazine hydrate demonstrating to be promising candidates as anodes in direct hydrazine alkaline anion-exchange membrane fuel cells (DHAFC). [ABSTRACT FROM AUTHOR]

Sulfur in the air stream is one of the major contaminants affecting the performance stability of cathodes of solid oxide fuel cells (SOFCs) such as La0.6Sr0.4Co0.2Fe0.8O3.δ (LSCF) perovskite. Here sulfur deposition and poisoning was investigated on LSCF bar samples in the presence of 20 ppm SO2 and temperature range of 400--900°C, using scanning electron microscopy, confocal laser Raman spectroscopy and electrical conductivity relaxation (ECR) methods. Sulfur (SO2) reacts with LSCF, primarily forming SrSO4 at high temperatures (i.e., ≥ 700°C) and SrS at low temperatures (i.e. <700°C). Surface segregated SrO plays an important role in the sulfur deposition. The most important observation of this study is that sulfur deposition shows a distinct volcano-type dependency on the heat-treatment temperature and is most pronounced at temperatures around 700°C, indicating that the reaction rate between the segregated SrO and SO2 is highest at ~700°C. The ECR results indicate that the surface exchange coefficient of LSCF after the exposure to 20 ppm SO2 at 700, 800 and 900°C for 48 h is two orders of magnitude lower than that of the sample tested in the absence of SO2, indicating that sulfur poisoning deteriorates significantly the surface exchange and diffusion processes for the O2 reduction reaction on LSCF electrodes. [ABSTRACT FROM AUTHOR]

Here, the chemical oxygen surface exchange coefficient and film stress of porous La0.6Sr0.4FeO3-δ (LSF64) thick films were simultaneously measured in situ between 275-375°C and 275-700°C, respectively, using a bilayer curvature measurement technique. The magnitude and activation energy of the porous LSF64 thick film oxygen surface exchange coefficients were consistent with those from large grained, bulk samples. However, unlike large-grained, dilatometry-tested bulk LSF64 samples that only exhibited measurable chemical stress above 525°C, the fine-grained, curvature-tested porous LSF64 thick films studied here exhibited measurable chemical stress over the complete temperature range from 275 to 700°C. Further, the porous LSF64 thick films exhibited a kink in their Arrhenius chemical stress behavior (displaying activation energies of 0.07 eV below 525°C and 0.5 eV above 525°C), suggesting a distinct lattice-dominated chemical stress response above 525°C and a distinct grain-boundary-dominated chemical stress response below 525°C. [ABSTRACT FROM AUTHOR]

In this work, La2Zr2O7 with a pyrochlore structure was doped with Sc, Y, Nd, Sm and Gd into its Zr-site to investigate the dependence of conduction behavior on the dopant. A systematic study was also performed to study the relationship between Y content and the proton conductivity. The results revealed that La2Zr2O7 doped with Y had higher conductivity, compared with those doped with Sc, Nd, Sm and Gd. Among the samples doped with various content of Y, La2(Zr0.9Y0.1)2O7-δ was identified to have a single pyrochlore phase, and exhibited the highest bulk conductivity of 3.68 × 10-4 Scm-1 at 600°C in wet H2. But such value is still not enough for the application as an electrolyte in fuel cells. Poor capability for water incorporation is one of the reasons restricting a further increase of the proton conductivity. [ABSTRACT FROM AUTHOR]

Symmetric cells (electrode/electrolyte/electrode) were prepared using BaCe0.2Zr0.7Y0.1O3-δ (BCZY27) as a proton conducting electrolyte. Porous BCZY27 backbones were sintered on each side of the electrolyte. Lanthanum nickelate, La2NiO4+δ (LN), was infiltrated into the porous BCZY27 backbone to act as the electrode. Pure phase LN was formed after annealing in air at 850°C for 4 h. Electron microscopy was used to observe LN nano-particles (~50 nm) infiltrated throughout the backbone. Impedance spectra were recorded at 500, 600, and 700°C with four oxygen partial pressures and four steam partial pressures. Four arcs were observed in the spectra corresponding to: BCZY27 backbone grain-boundary resistance, charge-transfer, oxygen dissociation/adsorption, and gas transport. Total area specific resistances (ASRs) were found to decrease with increasing oxygen partial pressure. Total cathode ASRs of 161.8, 29.3, and 3.7 Ω⋅cm² were measured in 3% humidified air at 500, 600, and 700°C respectively. [ABSTRACT FROM AUTHOR]

We investigated the catalytic activities of three perovskite oxide (LaMnO3, La0.8Sr0.2MnO3, and La0.8Sr0.2CoO3) thin films grown by pulsed laser deposition when they were used as oxygen electrodes for aqueous rechargeable metal-air batteries. The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on perovskite oxide thin films in alkaline solution were observed by linear sweep voltammetry using a rotating disk electrode. Although we confirmed that the resultant perovskite oxide thin films were sufficiently electroconductive to facilitate the ferricyanide reduction reaction on themselves, the ORR activities of perovskite oxide thin films were much lower than those of conventional composite electrodes, which consist of perovskite oxide powder and carbon black. In contrast, the OER activities of thin films and their activity order (La0.8Sr0.2CoO3 > LaMnO3 ≥ La0.8Sr0.2MnO3) were almost the same as those of conventional composite electrodes. We discuss the catalytic roles of perovskite oxides and carbon powder in oxygen electrodes and propose possible reaction paths for the ORR and OER. [ABSTRACT FROM AUTHOR]

La0.6Sr0.4Fe0.8Cu0.2O3-δ was prepared via combined EDTA-citrate complexing sol-gel process, characterized by X-ray diffraction and SEM. Ammonia synthesis was successfully synthesized directly from wet nitrogen based on an electrolytic cell using La0.6Sr0.4Fe0.8Cu0.2O3-δ-Ce0.8Gd0.18Ca0.02O2-δ composite cathode, Ce0.8Gd0.18Ca0.02O2-δ-(Li/Na/K)2CO3 composite electrolyte and Sm0.5Sr0.5CoO3-δ-Ce0.8Gd0.18Ca0.02O2-δ composite anode. The O2- conduction of the composite electrolyte was used for ammonia synthesis. The maximum ammonia formation rate of 5 x 10-11 mol s-1 cm-2 was observed at 400°C when a voltage of 1.4 V was applied which is two orders of magnitude higher than that of previous report when ammonia was synthesized from N2 and H2O at 650°C. Besides ammonia, hydrogen is also co-generated at the cathode. [ABSTRACT FROM AUTHOR]

Layered perovskites have attracted abundant interest as advanced cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) due to their high electrical conductivity and excellent catalytic properties for the oxygen reduction reaction (ORR). However, cobalt related layer perovskite oxides generally suffer from larger thermal expansion co-efficiency (TEC) than that of electrolyte materials. In this study, we have prepared a thin interlayer, SmBa0.5Sr0.5Co2O5+δ (SBSCO) layered perovskite, via pulsed laser deposition (PLD) on a Sr- andMg- doped LaGaO3 (LSGM) thin film electrolyte to prevent the formation of a micro-gap arising from the thermal mismatch between the SBSCO cathode and LSGM electrolyte. A Samaria-doped ceria (SDC) buffer layer was prepared between the cathodic interlayer and LSGM electrolyte in order to prevent interdiffusion of cations. The cathodic interlayer of SBSCO is helpful for overcoming the thermal mismatch between the SBSCO powder cathode and the LSGM electrolyte, and also shows high power generating properties and small area specific resistance under typical fuel cell operating conditions. [ABSTRACT FROM AUTHOR]

The oxygen electrode is a vital element in developing lithium-oxygen batteries, because it provides the active sites for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In addition, the performance of the oxygen electrode strongly depends on the activity and architecture of materials employed. Perovskite oxide nanostructures of nickel-doped lanthanum cobaltite were prepared by a very simple and cost-effective solution combustion synthesis. The oxygen electrode containing a carbon-supported perovskite oxide catalyst with oxygen vacancies exhibited reduced polarization and improved discharge capacity compared with that containing only bare carbon without a catalyst. In particular, the LaNi0.25Co0.75O3-δ catalyst showed the best catalytic activity for OER by achieving the oxidation of Li2O2 at 3.8 V. The widespread dispersion and mesoporous design of perovskite facilitates the diffusion of electrolyte and oxygen into the inner electrode to demonstrate cyclability for 49 cycles while maintaining a moderate specific capacity of 1000 mAh g-1. Further, the synergistic effect of the fast kinetics of electron transport provided by the carbon support and the high electro-catalytic activity of the perovskite oxide resulted in excellent performance of the oxygen electrode for Li-O2 batteries. [ABSTRACT FROM AUTHOR]

Lanthanum silicates La10Si6−xMgxO27−x (x = 0–0.4) were prepared by solid state synthesis to investigate the effect of Mg doping on crystal structure and ionic conductivity. Rietveld analysis of the powder XRD patterns reveals that Mg substitution on Si site results in significant enlargement of channel triangles, favoring oxide-ion conduction. Furthermore, an increase of Mg concentration significantly influences the linear density of interstitial oxygen, which plays an important role in ionic conductivity. The Arrhenius plots of La10Si6−xMgxO27−x (x = 0–0.4) suggest that Mg-doped samples present higher conductivity and lower activation energy than non-doped La10Si6O27, and La10Si5.8Mg0.2O26.8 exhibits the highest conductivity with a value of 3.0×10−2 S ·cm−1 at 700 °C. Such conductive behavior agrees well with the refined results. The corresponding mechanism has been discussed in this paper. [ABSTRACT FROM AUTHOR]

Porous La1-xSrxCoO3-Ω (LSC/electrodes with Sr composition x = 0.2 (LSC-82) and x = 0.4 (LSC-64) were prepared by screen- printing LSC powders onto rare-earth doped ceria electrolytes, followed by sintering at 950 ~ 1100°C, and characterization using scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface-area analysis, 3-D morphological imaging based on focused ion beam scanning electron microscopy (FIB-SEM), and energy dispersion X-ray spectroscopy (EDX/EDS). The batch-to- batch variability and degradation (over 1000 ~ 2000 hours) of the electrochemical performance of these cells were studied using electrochemical impedance spectroscopy (E1S) and measurements of nonlinear electrochemical impedance (NLEIS). These mea- surenaents reveal a strong correlation between the characteristic frequency (ωc) and characteristic resistance (Rc) of the electrodes, which, when analyzed in light of microstructural data, indicates that performance variability and degradation are caused primarily by variations in the surface rate coefficient k(T) for O2 exchange. [ABSTRACT FROM AUTHOR]

Ni composite anodes for Ca-doped LaNbO4 (LCNO) based proton conducting solid oxide fuel cells were fabricated as screen-printed Ni-LCNO cermets on a dense self-supported LCNO electrolyte and as a semi-symmetrical cell consisting of a ~ 15 µm thick LCNO electrolyte deposited on a tape-cast Ni-LCNO anode support. The influence of Ni content and sintering temperature on the polarization resistance of the Ni-LCNO interface was investigated. The interface was characterized by electrochemical impedance spectroscopy, and the effects of temperature, pO2 and pH2O on the area specific resistance (ASR) at open circuit were used to determine the rate limiting steps of the hydrogen kinetics of these anodes. The total electrode response is 1.1 Ωcm² for 40/60 (vol) Ni/LCNO cermet support, at 800°C in wet H2, and the activation energy ~ 0.5 eV. Three processes were suggested to contribute to the polarization resistance of Ni-LCNO cermet anodes, the most resistive believed to correspond to a charge transfer process at the interface between hydrogen atoms on or in Ni and protons in the electrolyte. [ABSTRACT FROM AUTHOR]

Thick La0.5Sr0.5CoO3-δ (LSCO) cathodes (~30 μm) have been successfully fabricated with and without nanoporous LSCO interlayers on both sides of a dense polycrystalline gadolinia-doped ceria (CGO) substrate by combining screen printing and pulsed laser deposition (PLD) methods. The electrochemical properties of these LSCO cathodes for oxygen reduction reaction have been determined by electrochemical impedance spectroscopy (EIS) at different interlayer thicknesses, temperatures, and oxygen partial pressures. The oxygen reduction reaction on the LSCO electrode with and without the interlayer has been found to be mainly limited by the surface exchange process. By fitting the power density data by Butler-Volmer equation, it demonstrates that as the thickness of the PLD interlayer increases, the surface exchange resistance of the cathode decreases due to a significant increase in the number of reaction sites obtained by inserting the nanoporous LSCO interlayer. [ABSTRACT FROM AUTHOR]

Novel heterostructured La2Zr2O7:Eu3+@YBO3 core@shell nanoparticles (NPs) composed of a trivalent europium doped lanthanum zirconate (La2Zr2O7:Eu3+) core and yttrium orthoborate (YBO3) shell are reported in this paper for the first time. X-ray diffraction, Fourier transform infrared spectroscopy, scanning and transmission electron microscopies, and x-ray photoelectron spectroscopy were employed to confirm the formation of the heterostructured core@shell NPs. Luminescent enhancement was observed after the La2Zr2O7:Eu3+ core NPs were coated with the thin YBO3 shells under 405 nm excitation. Based on optical transition property analysis and fluorescent decay measurement, the reduction of non-radiative transition rate is possibly responsible for the luminescent enhancement. Moreover, an improvement of the symmetry around the Eu3+ ions in the La2Zr2O7:Eu3+ core NPs was found after the YBO3 shell coating. [ABSTRACT FROM AUTHOR]

The alternation from bipolar to unipolar resistive switching is observed in perovskite La0.01Sr0.99TiO3 thin films. These two switching modes can be activated separately depending on the compliance current (Icomp) during the electro-forming process: with a higher Icomp (5 mA) the unipolar resistance switching behavior is measured, while the bipolar resistance switching behavior is observed with a lower Icomp (1 mA). On the basis of I—V characteristics, the switching mechanisms for the URS and BRS modes are considered as being a change in the Schottky-like barrier height and/or width at the Pt/La-SrTiO3 interface and the formation and disruption of conduction filaments, respectively. [ABSTRACT FROM AUTHOR]

Local electrical conduction behaviors of polycrystalline La-doped BiFeO3 thin films have been investigated by combining conductive atomic force microscopy and piezoelectric force microscopy. Nanoscale current measurements were performed as a function of bias voltage for different crystal grains. Completely distinct conducting processes and resistive switching effects were observed in the grain boundary and grain interior. We have revealed that local electric conduction in a grain is dominated by both the grain boundary and ferroelectric domain, and is closely related to the applied electric field and the as-grown state of the grain. At lower voltages the electrical conduction is dominated by the grain boundary and is associated with the redistribution of oxygen vacancies in the grain boundary under external electric fields. At higher voltages both the grain boundary and ferroelectric domain are responsible for the electrical conduction of grains, and the electrical conduction gradually extends from the grain boundary into the grain interior due to the extension of the ferroelectric domain towards the grain interior. We have also demonstrated that the conduction dominated by the grain boundary exhibits a much small switching voltage, while the conduction of the ferroelectric domain causes a much high switching voltage in the grain interior. [ABSTRACT FROM AUTHOR]

A p-n junction composed of Ag+-doped manganite Lao.8Ago.2MnO3/SrTiO3(LAMO) and Nb-0.5wt%-doped SrTiO3(STON) was fabricated using the pulsed laser deposition method. The heterojunction exhibits a good rectifying prop-erty over a wide temperature range from 20 to 390K. The minimum diffusion potential and the lowest leakage currents under different negative voltages both occur at 320 K, which is around the metallic-insulator transition temperature of the LAMO ßlm. The photovoltage rises with the decreasing temperature and wavelength of the laser beam. Under the illumination of a 473nm laser beam, the photovoltage grows as the light power increases and seems to be saturated at about 300mW. The maximum VOC is 0.76 V, which is close to the diffusion voltage. [ABSTRACT FROM AUTHOR]

Cathodic electrodeposition of La(OH)3 from lanthanum nitrate bath was performed for the first time. The deposition experiments were conducted at the pulse current mode with a typical on-time and off-time (ton = 5 s and toff = 10s) and an average current density of 1 mA cm-2 (Ia = 1 mA cm-2) for 50 min. The prepared deposit was then heat treated at 600°C for 3h in dry air atmosphere. The products were characterized by XRD, CHN, FT-IR and SEM techniques. The results revealed that the large scale and vertically aligned one-dimensional (1D) La(OH)3 nanorods have been prepared at the applied conditions. It is also seen that heat-treatment of the prepared hydroxide nanorods resulted the La2O3 nanorods without any change in their morphology. By recording the potential-time curve during the electrodeposition process, it was fund that water reduction reaction has the major role in the electrogeneration of base at the cathode surface. Based on the H2 bubbling on the cathode surface, the mechanism of the formation and the growth of La(OH)3 nanorods was proposed and discussed. Results of this work showed that large-scale, uniform and vertically aligned nanorods of La(OH)3 and La2O3 are achievable by pulse electrodeposition followed by heat-treatment. [ABSTRACT FROM AUTHOR]

We have grown superconducting epitaxial thin films of LaNixBi2 which crystallize in the ZrCuSiAs structure with a peculiar Bi square net layer. This material represents an additional class of pnictide superconductors since superconductivity is assumed to occur in the Bi square net layer. Optimized thin films grown by molecular beam epitaxy have a superconducting transition temperature of around 4 K and are stable in ambient air. [ABSTRACT FROM AUTHOR]

The formation and diffusion of vacancies are studied in LaAlO3/SrTiO3 heterostructures. Oxygen vacancies (VOS) appear easily in the SrTiO3 substrate during LaAlO3 film growth at 700 °C and 10-4 Pa oxygen pressure rather than at 10-3-10-1 Pa, thus the latter two-dimensional electron gas should come from the polarity discontinuity at the (LaO)+/(TiO2)0 interface. For SrTiO3-δ/LaAlO3/SrTiO3, high-density VOS of the SrTiO3-δ film can pass through the LaAlO3 film and then diffuse to 1.7μm depth in the SrTiO3 substrate, suggesting that LaAlO3 has VOS at its middle-deep energy levels within the band gap. Moreover, high-density VOS may combine with a strontium/titanium vacancy (VSr/Ti) to form VSr/Ti-O complexes in the SrTiO3 substrate at 700°C. [ABSTRACT FROM AUTHOR]

LaFeO3 was prepared by the microwave-assisted citrate method and the catalytic activity for oxygen evolution reaction was investigated in HClO4 solution. The prepared sample was characterized by XRD, HRTEM and FESEM. XRD data showed that pure perovskite phase was indeed formed. The results suggested the successful incorporation of Fe3+ at the La3+ cations sites confirming the formation of the orthorhombic perovskite phase of LaFeO3. The particle size calculated from Scherrer equation was found to be 80.56 nm. The HRTEM picture also ascertained the orthorhombic phase and the particle size. FESEM image showed a porous and rough surface. Anodic linear polarization was used to evaluate the catalytic activity. The presence of the perovskite modifier increased the electrocatalytic activity toward oxygen evolution reaction (OER) by about 100 times, the current densities obtained at 1.5 V are 3.6 x 10-5 and 1.2 x 10-3 A/cm² for unmodified and modified surfaces, respectively. The order of reaction with respect to [H+] is close to unity and the calculated activation energy is 20 kJ/mol, which is much less than the values reported for several catalysts used for OER including some precious metal oxides. EIS results proved the high electrocatalytic activity of LaFeO3 toward OER. [ABSTRACT FROM AUTHOR]

Perovskites based upon substituted LaCoO3-δ are the state-of-the-art materials for a variety of different devices for moderate high temperature applications such as solid oxide fuel cells (SOFCs) and mixed ionic and electronic conducting (MIEC) membranes. The unique feature of the oxides is their ability to undergo both thermal expansion and that induced by the defects of oxygen nonstoichiometry in the oxide lattice. The latter is chemical or defect-induced expansion. This property is extremely sensitive to the defect structure of the oxide material. Therefore reliable data on the defect structure of oxide materials is of key importance to understanding the origin of their chemically induced lattice strain. On the other hand, chemical expansion of oxide crystal cell precisely measured with ppm-resolution allows better understanding its local electronic and defect structure. [ABSTRACT FROM AUTHOR]

We reexamined the experimental evidence for the possible existence of superconducting (SC) gap nodes in the three most suspected Fe-pnictide SC compounds: LaFePO, BaFe2(As0.67P0.33)2, and KFe2As2. We showed that while the T-linear temperature dependence of the penetration depth λ(T) of these three compounds indicates extremely clean nodal gap superconductors, the thermal conductivity data limT,H→0 kS(H,T)/T unambiguously showed that LaFePO and BaFe2(As0.67P0.33)2 are extremely dirty, while KFe2As2 can possibly be clean. These apparently conflicting experimental data cast a serious doubt on the nodal gap possibility for LaFePO and BaFe2(As0.67P0.33)2. [ABSTRACT FROM AUTHOR]

We reexamined the experimental evidence for the possible existence of superconducting (SC) gap nodes in the three most suspected Fe-pnictide SC compounds: LaFePO, BaFe2(As0.67P0.33)2, and KFe2As2. We showed that while the T-linear temperature dependence of the penetration depth λ(T) of these three compounds indicates extremely clean nodal gap superconductors, the thermal conductivity data limT,H→0 kS(H,T)/T unambiguously showed that LaFePO and BaFe2(As0.67P0.33)2 are extremely dirty, while KFe2As2 can possibly be clean. These apparently conflicting experimental data cast a serious doubt on the nodal gap possibility for LaFePO and BaFe2(As0.67P0.33)2. [ABSTRACT FROM AUTHOR]

Positron emission tomography detectors based on monolithic scintillation crystals exhibit good spatial and energy resolution, intrinsically provide depth-of-interaction information, have high γ -photon capture efficiency, and may reduce the manufacturing costs compared to pixelated crystal arrays. Here, we present the characterization of a detector consisting of a 18.0 mm×16.2 mm×10.0 mm monolithic LaBr3:5%Ce scintillator directly coupled to a 4×4 array of silicon photomultipliers. An energy resolution of 6.4% full-width-at-half-maximum (FWHM) was obtained. The point-spreadfunction (PSF) was determined for different regions of the detector. The fullwidth-at-half-maximum (FWHM) of the PSF was measured to be <1.5 mm at the center of the detector and <1.7 mm averaged over the entire crystal. Both values are not corrected for the ˜0.6 mm FWHM test beam diameter. Furthermore, the influence of edge effects was investigated. We found that near the edges of the detector the spatial resolution degrades to 2.2 mm (FWHM), and a bias in the position estimates, up to 1.5 mm, was observed. Moreover, the coincidence resolving time for two identical detectors in coincidence was measured to be as small as ˜198 ps FWHM. [ABSTRACT FROM AUTHOR]

Oxygen vacancy formation and migration in La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) with various crystal symmetries (cubic, rhombohedral, orthorhombic, and monoclinic) are studied by employing first-principles calculations based on density functional theory (DFT). It is shown that the cubic LSGM has the smallest band gap, oxygen vacancy formation energy, and migration barrier, while the other three structures give rise to much larger values for these quantities, implying the best oxygen ion conductivity of the cubic LSGM among the four crystal structures. In our calculations, one oxygen vacancy migration pathway is considered in the cubic and rhombohedral structures due to all the oxygen sites being equivalent in them, while two vacancy migration pathways with different migration barriers are found in the orthorhombic and monoclinic symmetries owing to the existence of nonequivalent O1 and O2 oxygen sites. The migration energies along the migration pathway linking the two O2 sites are obviously lower than those along the pathway linking the O1 and O2 sites. Considering the phase transitions at high temperatures, the results obtained in this paper can not only explain the experimentally observed different behaviours of the oxygen ionic conductivity of LSGM with different symmetries, but also predict the rational crystal structures of LSGM for solid oxide fuel cell applications. [ABSTRACT FROM AUTHOR]

The crystallographic structure and magnetic properties of La(Fe11:4Al1:6)C0:02 are studied by magnetic measurement and powder neutron diffraction with temperature and applied magnetic field. Rietveld refinement shows that La(Fe11:4Al1:6)C0:02 crystallizes into the cubic NaZn13-type with two different Fe sites: FeI (8b) and FeII (96i), and that Al atoms preferentially occupy the FeII site. A ferromagnetic state can be induced at a medial temperature of 39 K-139 K by an external magnetic field of 0.7 T, and a large lattice is correspondingly found at 100 K and 0.7 T. In all other conditions, La(Fe11:4Al1:6)C0:02 has no net magnetization in the paramagnetic (T > TN = 182 K) or antiferromagnetic states, and thus keeps its small lattice. Analysis of the Fe-Fe bond length indicates that the ferromagnetic state prefers longer Fe-Fe distances. [ABSTRACT FROM AUTHOR]

We studied the critical state stability of a large cubic sample of single-crystalline La1.85Sr0.15CuO4 for different sample orientations with respect to the external magnetic field as well as the dynamics of the flux jumps. It is shown that thermomagnetic avalanches develop under dynamic conditions, which are characterized by the magnetic diffusivity being significantly lower than the thermal case. In this case, the critical state stability depends strongly on the cooling conditions. We compared predictions from the isothermal model and from the model for a weakly cooled sample with experimental results. In both models, the field of the first flux jump decreases with increase of the sweep rate of the external magnetic field. We also investigated the influence of the external magnetic field on the dynamics of the following stages of the thermomagnetic avalanche. It is shown that the dynamics of the flux jumps is correlated with the magnetic diffusivity, which is proportional to the flux flow resistivity. [ABSTRACT FROM AUTHOR]

We studied the critical state stability of a large cubic sample of single-crystalline La1.85Sr0.15CuO4 for different sample orientations with respect to the external magnetic field as well as the dynamics of the flux jumps. It is shown that thermomagnetic avalanches develop under dynamic conditions, which are characterized by the magnetic diffusivity being significantly lower than the thermal case. In this case, the critical state stability depends strongly on the cooling conditions. We compared predictions from the isothermal model and from the model for a weakly cooled sample with experimental results. In both models, the field of the first flux jump decreases with increase of the sweep rate of the external magnetic field. We also investigated the influence of the external magnetic field on the dynamics of the following stages of the thermomagnetic avalanche. It is shown that the dynamics of the flux jumps is correlated with the magnetic diffusivity, which is proportional to the flux flow resistivity. [ABSTRACT FROM AUTHOR]

La0.8Sr0.2ScxMn1-xO3−δ–yttria stabilized zirconia composite anodes were synthesized by infiltration and investigated as alternative anodes for intermediate solid oxide fuel cells. Non-stoichiometric variation of oxygen content and electrical conductivity in La0.8Sr0.2ScxMn1-xO3−δ–yttria stabilized zirconia composite was studied by high temperature coulometric titration at 923–1023 K. La0.8Sr0.2ScxMn1-xO3−δ shows an oxygen deficient composition depending on the oxygen partial pressure, temperature, and Sc content. A defect chemistry model is presented by taking into consideration the interaction of randomly distributed defects, Sr’La,V ö, OXO, MnXMn, Mn·Mn and ScXMn. The proposed defect model fits well with experimental non-stoichiometric data. The interaction among the defects for vacancy formation is strongly influenced by the amount of dopant, Sc content, and temperature. The thermodynamic properties, oxidation enthalpy ΔH and entropy ΔS, were obtained from the oxygen isotherms. The electrical conductivities measured by the 4-probe method as a function of oxygen partial pressure and temperature were high enough for composite anode application. [ABSTRACT FROM AUTHOR]

We explore the electrical transport and magneto-conductance (MC) in quasi-two-dimensional strongly correlated ultra-thin films of LaNiO3 (LNO) to investigate the effect of hetero-epitaxial strain on electron-electron and electron-lattice interactions from the low to intermediate temperature range (2-170 K). The fully epitaxial 10 unit cell thick films spanning tensile strain up to ~4% are used to investigate the effects of enhanced carrier localization driven by a combination of weak localization (WL) and electron-electron interactions at low temperatures. The MC data show the importance of the increased contribution of WL to low-temperature quantum corrections. The obtained results demonstrate that with increasing tensile strain and reduced temperature, the quantum-confined LNO system gradually evolves from the Mott into the Mott-Anderson regime. [ABSTRACT FROM AUTHOR]

In this study, construction of a new lanthanum selective disk electrode based on benzo-15-crown-5 (B15C5) as a neutral carrier has been described. The electrode has been composed of 2.5 mg of Benzo-15-crown5 as an ionophore, 7 mg of oleic acid (OA) as an additive, 60.5 mg of ortho-nitrophenyloctyl ether (NPOE) as a plasticizer, and 30 mg of polyvinyl chloride (PVC) as the membrane supporting matrix. The electrode shows a linear dynamic response in the concentration range of 5 × 10-7 to 1 × 10-2 M with a Nernstian slope of 19.5 mV per decade and a detection limit of 8.74 × 10-7 M. It has a response time of <15 s and can be used for at least 5 months without any significant divergence in potentials. The selectivity coefficients for mono, di, and trivalent cations indicate a good selectivity for La(III) ions over a large number of interfering cations. It could be used in a pH range of 3.0-6.0. The proposed electrode was applied as an indicator electrode in potentiometric titration of fluoride ion and also used for determination of F- ion in mouthwash solution, tap water and toothpaste samples. [ABSTRACT FROM AUTHOR]

We explore the electrical transport and magneto-conductance (MC) in quasi-two-dimensional strongly correlated ultra-thin films of LaNiO3 (LNO) to investigate the effect of hetero-epitaxial strain on electron-electron and electron-lattice interactions from the low to intermediate temperature range (2-170 K). The fully epitaxial 10 unit cell thick films spanning tensile strain up to ~4% are used to investigate the effects of enhanced carrier localization driven by a combination of weak localization (WL) and electron-electron interactions at low temperatures. The MC data show the importance of the increased contribution of WL to low-temperature quantum corrections. The obtained results demonstrate that with increasing tensile strain and reduced temperature, the quantum-confined LNO system gradually evolves from the Mott into the Mott-Anderson regime. [ABSTRACT FROM AUTHOR]

Highly dense pellets of an oxygen excess-type lanthanum silicate (La9.333+xSi6O26+1.5x, x > ca. 0.3, OE-LSO) were successfully fabricated, and their electrical conducting properties were studied. The replacement of Si by Al enhanced its conductivity, and the slightly Al-doped OE-LSO specimen [La9.62(Si5.79Al0.21)O26.33] had excellent features as a solid electrolyte; that is, it had high ionic conductivity and was highly stable under reducing as well as oxidizing conditions at 873-1073 K. In addition, the ionic transference number was higher than 0.99. In the fuel cell utilizing this electrolyte (0.72 mm thick), (La0.6Sr0.4)(Co0.2Fe0.8)O3-δ cathode, and Ni-Ce0.9Gd0.1O1.95-δ anode, good performance with the maximum power density of ca. 0.25 W cm-2 was obtained at 1073 K. In addition, this electrolyte also had high compatibility with these conventional mixed conducting electrodes, according to an analysis near the electrode/electrolyte interfaces after the fuel cell test. [ABSTRACT FROM AUTHOR]

Electrolysis of H2O, CO2, and co-electrolysis of H2O and CO2 was studied in Ni/yttria-stabilized zirconia (YSZ) electrode supported solid oxide electrolysis cells (SOECs) consisting of a Ni/YSZ support, a Ni/YSZ electrode layer, a YSZ electrolyte, and an lanthanum strontium manganite (LSM)/YSZ oxygen electrode When applying the gases as received, the cells degraded significantly at the Ni/YSZ electrode, whereas only minor (and initial) degradation was observed for either the Ni/YSZ or LSM/YSZ electrode. Application of clean gases to the Ni/YSZ electrode resulted in operation without any long-term degradation, in fact some cells activated slightly. This shows that the durability of these SOECs is heavily influenced by impurities in the inlet gases. Cleaning the inlet gases to the Ni/YSZ electrode may be a solution for operating these Ni/YSZ-based SOECs without long-term degradation. [ABSTRACT FROM AUTHOR]

Electrochemical data collected for the porous La1-xSrxMnO3±δ (LSM) cathode-yttria-stabilized zirconia electrolyte system were analyzed using a mathematical model capable of simulating both the steady-state and impedance responses. he model considered the distributed nature of the porous electrode and a parallel pathway for oxygen transport including gas transport and surface diffusion. Data were collected in low oxygen partial pressures ranging between 10-4 and 10-3 atm, where LSM was considered to be stoichiometric with respect to oxygen. Thermodynamically consistent kinetic and transport parameters were regressed from the steady-state polarization data. Three different parameter sets fit the general trend of the experimental data. The surface diffusion and adsorption/desorption parameters were cross-correlated, which underlines the difficulty in finding a, unique Set of fitting parameters. The parameter set with four adjustable parameters resulted in a high surface diffusion coefficient but slower adsorption/desorption kinetics compared to the other two parameter sets for which a lower surface diffusion coefficient was fixed. The predicted overall impedance at zero-dc bias conditions for three parameter sets had varying degrees of agreement with the data. Low and high frequency arcs attributed to adsorption and an oxygen transport process were observed in the faradaic impedance response. [ABSTRACT FROM AUTHOR]

A numerical model was proposed to simulate the electrochemical behavior of strontium-doped lanthanum manganite (LSM) under cathodic polarization by assuming the transient variation of oxygen concentration and the defect chemistry of LSM. From the simulation, it was revealed that the dynamic response of cathodic potential proceeded in two steps with different time domains. A drastic change in cathodic potential occurred soon after the current loading. In addition, the oxygen nonstoichiometry in LSM changed simultaneously, resulting in an enhancement in the electrochemical performance of the LSM cathode. The simulated phenomenon was validated by experimental results. [ABSTRACT FROM AUTHOR]

Recently, both electrical and material properties of lanthanum oxide (La2O3) have been found to significantly improve with a trace amount of nitrogen doping. This work conducted a detailed investigation on the nitrogen incorporation at the La2O3/Si interface by using X-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements. The process-dependent chemical bonding structures of Si-O, and La atoms at the interlace were studied in detail. For samples annealed at 500°C and above, the interlacial metallic La-Si bonds were converted into La-N bonds, and some Si-O bonds were found at the interface. These effects resulted in a significant reduction in the interface trap density. The bulk properties of La2O3 were also improved with the proposed techniaue as a result of the filling of oxygen vacancies with nitrogen atoms. [ABSTRACT FROM AUTHOR]

This paper compares the effects of Ni and Ru dopants in lanthanum chromite anodes by correlating structural characterization and electrochemical measurements in solid oxide fuel cells (SOFCs). Transmission electron microscope observations showed that nanoclusters of Ni or Ru metal precipitated onto lanthanum chromite (La0.8Sr0.2Cr1-yXyO3-δ, X = Ni,Ru) surfaces, respectively, after exposure to hydrogen at 750-800°C. Ni nanoclusters were typically 10 nm in diameter immediately after reduction and coarsened to -50 nm over ∼ 300 h at 800°C. In contrast, Ru cluster size was stable at ∼ 5 nm, and the cluster density was > 10 times larger. SOFC tests were done with the doped lanthanum chromite anodes on La0.8Sr0.2Cr1-yXyO3-δ electrolyte-supported cells. Ni nanocluster nucleation improved cell performance and reduced anode polarization resistance compared to cells with undoped (La0.8Sr0.2Cr1-yXyO3-δ) anodes, but the improvement was much less than that for Ru. This comparison suggests that the smaller size of the Ru nanoclusters played an important role in enhancing anode electrochemical kinetics. [ABSTRACT FROM AUTHOR]