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Cubic Li7La3Zr2O12 (LLZO) garnets are among the most promising solid-state electrolytes for next-generation Li batteries. However, despite intensive research in recent years, little effort is spent on proper chemical analysis of the material. For reliable LLZO investigation, knowledge about the exact chemical composition, especially the Li content, is of uttermost importance. Herein, we present a method for the laterally resolved stoichiometry determination of Al stabilized LLZO (Li7−3xAlxLa3Zr2O12) using LA-ICP-OES. To ensure reliable signal quantification, matrix-matched standards are prepared and carefully characterized using sample digestion and liquid ICP-OES measurement. An internal standard-independent calibration strategy based on 100 m% normalization is applied, enabling the quantification of all cations within the material. By comparing the obtained high-precision LA-ICP-OES calibrations with analog LA-ICP-MS measurements, it is shown that ICP-OES is the superior choice for the analysis of Li. The developed method is applied to record quantitative distribution images of an Al stabilized LLZO pellet, revealing macroscopic stoichiometry variations within the sample. To verify the analysis, the average stoichiometry obtained by the LA measurements is compared with the bulk composition determined via liquid ICP-OES analysis after sample fusion. The obtained values show excellent agreement, confirming the accuracy of the developed method. [ABSTRACT FROM AUTHOR]

Owing to its extraordinary high activity for catalysing the oxygen exchange reaction, strontium doped LaCoO3 (LSC) is one of the most promising materials for solid oxide fuel cell (SOFC) cathodes. However, under SOFC operating conditions this material suffers from performance degradation. This loss of electrochemical activity has been extensively studied in the past and an accumulation of strontium at the LSC surface has been shown to be responsible for most of the degradation effects. The present study sheds further light onto LSC surface changes also occurring under SOFC operating conditions. In-situ near ambient pressure X-ray photoelectron spectroscopy measurements were conducted at temperatures between 400 and 790 °C. Simultaneously, electrochemical impedance measurements were performed to characterise the catalytic activity of the LSC electrode surface for O2 reduction. This combination allowed a correlation of the loss in electro-catalytic activity with the appearance of an additional La-containing Sr-oxide species at the LSC surface. This additional Sr-oxide species preferentially covers electrochemically active Co sites at the surface, and thus very effectively decreases the oxygen exchange performance of LSC. Formation of precipitates, in contrast, was found to play a less important role for the electrochemical degradation of LSC. [ABSTRACT FROM AUTHOR]

In this study, the steady state current-overpotential (I-η) characteristics of the oxygen reduction reaction on the system Pt∣yttria-stabilized zirconia (YSZ) were investigated at temperatures between 600 and 720°C. The I- curve of Pt thin-film model electrodes on YSZ (100) exhibited a quite unexpected behavior, with diffusion limitation at lower and an exponential I- relationship at high cathodic polarization. This situation was interpreted in terms of two parallel electrochemical oxygen reduction pathways. The diffusion limited path - with an activation energy of the limiting current of 1.57 eV - is attributed to a classical surface path on Pt with diffusion through an impurity phase at the triple phase boundary (TPB) being rate limiting. Stoichiometry polarization is most likely responsible for the exponential part of the I- curve. In the corresponding second pathway, the oxygen reduction takes place on the YSZ surface with a rate limiting electron supply via the YSZ electrolyte. This interpretation is further supported by good accordance of the obtained activation energy (3.65 eV) with the activation energy of electronic conductivity in YSZ. The data can be used to calculate current contributions in broad temperature and overpotential ranges. [ABSTRACT FROM AUTHOR]

The impact of UV irradiation on Fe‐doped SrTiO3 (Fe:STO) single crystals is investigated at elevated temperatures. Illumination leads to incorporation of oxygen into the single crystals and thus to a decreasing oxygen vacancy concentration and oxidation of Fe3+ to Fe4+. The Fe4+ ions cause a color change from transparent/brownish to black. This photochromic blackening due to stoichiometry changes at elevated temperatures is irreversible at room temperature, but annealing at high temperatures, for example at 700 °C, can restore the original stoichiometry and color. Absorbance changes due to UV irradiation are monitored by ex situ and in situ UV–vis spectroscopy experiments and changes in electrical properties are measured by van der Pauw measurements and in‐plane electrochemical impedance spectroscopy. After 1140 min of illumination at 440 °C, for example, electrical measurements reveal a conductivity increase by more than a factor of 5 due to the enhanced hole concentration in blackened Fe:STO. In addition, UV illumination increases the oxygen chemical potential up to a calculated p(O2) of more than 109 Pa in Fe:STO. Hence, UV light can be used to tune the color, but also electrical properties of Fe:STO by directly impacting the bulk defect concentrations. [ABSTRACT FROM AUTHOR]

Advanced materials such as complex metal oxides are used in a wide range of applications and have further promising perspectives in the form of thin films. The exact chemical composition essentially influences the electronic properties of these materials which makes correct assessment of their composition necessary. However, due to high chemical resistance and in the case of thin films low absolute analyte amounts, this procedure is in most cases not straightforward and extremely time-demanding. Commonly applied techniques either lack in ease of use ( i.e. , solution-based analysis with preceding sample dissolution), or adequately accurate quantification ( i.e. , solid sampling techniques). An analysis approach which combines the beneficial aspects of solution-based analysis as well as direct solid sampling is Laser Ablation of a Sample in Liquid (LASIL). In this work, it is shown that the analysis of major as well as minor sample constituents is possible using a novel online-LASIL setup, allowing sample analysis without manual sample handling after placing it in an ablation chamber. Strontium titanate (STO) thin layers with different compositions were analyzed in the course of this study. Precision of the newly developed online-LASIL method is comparable to conventional wet chemical approaches. With only about 15–20 min required for the analysis per sample, time demand is significantly reduced compared to often necessary fusion procedures lasting multiple hours. [ABSTRACT FROM AUTHOR]

The impact of UV light (λ = 365 nm) on defect chemistry and composition of undoped SrTiO 3 single crystals was investigated by means of impedance spectroscopy. In-plane conductivity measurements between 280 and 450 °C in air reveal a drastic increase of the bulk conductivity upon UV illumination. The measured time dependence of this increase is in accordance with oxygen chemical diffusion in SrTiO 3. The corresponding photo-induced change in defect concentrations is caused by oxygen being pumped from the gas phase into the oxide under UV irradiation. This affects the entire SrTiO 3 crystal rather than only the thin UV absorption zone and leads to very high oxygen chemical potentials with nominal oxygen pressures up to 106 bar. After switching the UV light off, the resulting conductivity increase relaxes extremely slowly due to slow surface exchange kinetics. A mechanistic model is introduced to explain the impact of UV light on the oxygen chemical potential as well as on the oxygen vacancy and hole/electron concentrations in semiconducting oxides, here SrTiO 3. This model is based on the formation of oxygen quasi-chemical potentials in the illuminated region. It is discussed how the interplay of four kinetic parameters causes the observed time-dependent stoichiometry and thus conductivity changes. • Interaction of strontium titanate with above-band-gap-energy light • A model explaining photo-ionic oxygen exchange • Oxygen quasi-chemical potentials act as driver for oxygen exchange and diffusion. • General applicability of the model to other mixed ionic electronic materials [ABSTRACT FROM AUTHOR]

The influence of UV illumination by the plasma plume on the substrate stoichiometry during pulsed laser deposition (PLD) was examined on the model perovskite S r T i O 3 (STO) by the means of in situ impedance spectroscopy during pulsed laser deposition (IPLD). In this manner, the evolution of the STO bulk conductivity was tracked at 300 ∘ C during STO thin film deposition and during deposition on a quartz cover to isolate illumination effects from deposition effects. These measurements revealed an increasing bulk conductivity during covered measurements. Impedance spectroscopy under applied bias voltages indicates that these changes are not caused by photovoltages but by an enhanced oxygen incorporation compensated by electron hole generation under UV illumination. This enhanced conductivity persists after illumination. The combination of across-plane and in-plane measurements further indicates the formation of a layered system, allowing to estimate conductivity and thickness of the newly formed oxygen vacancy deficient layer. This results in a ∼ 30 times more conductive top layer with a thickness of ∼ 40 μ m. The driving force induced by the UV illumination which is responsible for this stoichiometry change corresponds to a p(O 2) difference of around six orders of magnitude. Results of in situ measurements show that the real deposition of a thin film leads to a more complex layered system where the growing film interacts with the illuminated top layer of the substrate and possibly introduces additional oxygen vacancies. These changes have a strong influence on any grown thin film either by oxidation/reduction potential or lattice parameter changes. [ABSTRACT FROM AUTHOR]