Chemical capacitance measurements are used to study the defect chemistry of La0.6Sr0.4FeO3–δ thin films and their polarization (η) and pO2 dependence. Important point defects are oxygen vacancies (), electrons (e′) and holes (h˙).

The electrochemical properties of La0.6Ba0.4CoO3-δ (LBC) and La0.6Sr0.4CoO3-δ (LSC) dense thin film model electrodes, deposited by pulsed laser deposition at 600°C on yttria-stabilized zirconia (100) electrolytes, were investigated by electrochemical impedance spectroscopy (EIS) at 450–600°C and 10−4 to 1 bar pO2. This comparative study reveals the influence of the A-site dopant size on the catalytic activity for the oxygen exchange, chemical capacitance and electronic conductivity. For both thin films the overall oxygen reduction is still limited by the oxygen surface exchange, although an extraordinarily high activity for the oxygen reduction reaction (ORR) was measured (LBC ∼0.18 Ωcm²/LSC ∼0.6 Ωcm² at 604°C and 0.21 bar pO2). Moreover, LBC exhibits a rather low activation energy for the ORR (1.19 ± 0.11 eV) together with a high electronic conductivity (839 S·cm−1 at ∼442°C). Based on these excellent electrochemical properties, LBC may also be a highly promising material for porous cathodes in intermediate temperature (400–600°C) solid oxide fuel cells.

We report the observation of second-harmonic generation (SHG) in stoichiometric silicon nitride waveguides grown via low-pressure chemical vapor deposition (LPCVD). Quasi-rectangular waveguides with a large cross section were used, with a height of 1 µm and various different widths, from 0.6 to 1.2 µm, and with various lengths from 22 to 74 mm. Using a mode-locked laser delivering 6-ps pulses at 1064 nm wavelength with a repetition rate of 20 MHz, 15% of the incoming power was coupled through the waveguide, making maximum average powers of up to 15 mW available in the waveguide depending on the waveguide cross section. Second-harmonic output was observed with a delay of minutes to several hours after the initial turn-on of pump radiation, showing a fast growth rate between 10 −4 to 10 −2 s −1 , with the shortest delay and highest growth rate at the highest input power. After this first, initial build-up (observed delay and growth), the second-harmonic became generated instantly with each new turn-on of the pump laser power. Phase matching was found to be present independent of the used waveguide width, although the latter changes the fundamental and second-harmonic phase velocities. We address the presence of a second-order nonlinearity and phase matching, involving an initial, power-dependent build-up, to the coherent photogal-vanic effect. The effect, via the third-order nonlinearity and multiphoton absorption leads to a spatially patterned charge separation, which generates a spatially periodic, semi-permanent, DC-field-induced second-order susceptibility with a period that is appropriate for quasi-phase matching. The maximum measured second-harmonic conversion efficiency amounts to 0.4% in a waveguide with 0.9 × 1 µm 2 cross section and 36 mm length, corresponding to 53 µW at 532 nm with 13 mW of IR input coupled into the waveguide. The according χ (2)-susceptibility amounts to 3.7 pm/V, as retrieved from the measured conversion efficiency.

Optoelectronic signal processing offers great potential for generation and detection of ultra-broadband waveforms in the THz range, so-called T-waves. However, fabrication of the underlying high-speed photodiodes and photoconductors still relies on complex processes using dedicated III-V semiconductor substrates. This severely limits the application potential of current T-wave transmitters and receivers, in particular when it comes to highly integrated systems that combine photonic signal processing with optoelectronic conversion to THz frequencies. In this paper, we demonstrate that these limitations can be overcome by plasmonic internal photoemission detectors (PIPED). PIPED can be realized on the silicon photonic platform and hence allow to leverage the enormous opportunities of the associated device portfolio. In our experiments, we demonstrate both T-wave signal generation and coherent detection at frequencies of up to 1 THz. To proof the viability of our concept, we monolithically integrate a PIPED transmitter and a PIPED receiver on a common silicon photonic chip and use them for measuring the complex transfer impedance of an integrated T-wave device.Terahertz signals (T-waves) offer promising perspectives for a wide variety of applications, comprising high-speed communications 1-3 , microwave photonics 4 , spectroscopy 5,6 , life sciences 7,8 , as well as industrial metrology 9,10 . Optoelectronic signal processing techniques are particularly attractive both for T-wave generation 1,11,12 and detection [13][14][15] , especially when broadband operation is required. On a conceptual level, optoelectronic T-wave generation relies on mixing of two optical signals oscillating at frequencies and b f in a high-speed photodetector, for which the photocurrent depends on the incident optical power 11 . The photocurrent oscillates with a difference frequency THz   Rx,1 U t modulates the device sensitivity. The PIPED photocurrent is then given by the product of the time-variant sensitivity with the time-variant optical power   Rx P t .

The oxygen incorporation and evolution reaction on mixed conducting electrodes of solid oxide fuel or electrolysis cells involves gas molecules as well as ionic and electronic point defects in the electrode. The defect concentrations depend on the gas phase and can be modified by the overpotential. These interrelationships make a mechanistic analysis of partial pressure-dependent current–voltage experiments challenging. In this contribution it is described how to exploit this complex situation to unravel the kinetic roles of surface adsorbates and electrode point defects. Essential is a counterbalancing of oxygen partial pressure and dc electrode polarization such that the point defect concentrations in the electrode remain constant despite varying the oxygen partial pressure. It is exemplarily shown for La0.6Sr0.4FeO3−δ (LSF) thin film electrodes on yttria-stabilized zirconia how mechanistically relevant reaction orders can be obtained from current–voltage curves, measured in a three-electrode setup. This analysis strongly suggests electron holes as the limiting defect species for the oxygen evolution on LSF and reveals the dependence of the oxygen incorporation rate on the oxygen vacancy concentration. A virtual independence of the reaction rate from the oxygen partial pressure was empirically found for moderate oxygen pressures. This effect, however, arises from a counterbalancing of defect and adsorbate concentration changes.

In this study, five different mixed conducting cathode materials were grown as dense thin films by pulsed laser deposition (PLD) and characterized via in-situ impedance spectroscopy directly after growth inside...

Electrochemical reactions at solid|gas interfaces of mixed ionic electronic conductors (MIEC), such as oxygen reduction or evolution, differ substantially from usual electrochemical reactions in aqueous solutions. Overpotentials do not directly translate to electrostatic surface potentials but act mainly by changing the concentration of point defects in the MIEC. This has severe consequences for the mechanistic interpretation of current voltage curves of MIEC electrodes. In this contribution it is shown how overpotential dependent defect concentrations affect the current-voltage curves of oxygen reduction and oxygen evolution at MIEC surfaces. Exemplarily, quantitative current-voltage curves are deduced from the known defect chemical data set (Brouwer diagram) of La 0.6 Sr 0.4 FeO 3−δ (LSF). Various curve shapes result, from Tafel-like exponential relations to essentially voltage independent limiting currents. Tafel slopes have a very different meaning compared to charge transfer limited reactions at metal electrode interfaces. It is shown how mechanistic information can be obtained from the difference of anodic and cathodic Tafel slopes or by comparing exchange current densities and ac resistances. Moreover, partial pressure dependences of anodic and cathodic currents are deduced, showing that exponents of power laws often do not indicate whether atomic or molecular oxygen species are involved in the rate limiting step.

Currently various new salts are synthesized to resolve problems associated with electrolytes of primary and secondary lithium batteries. The latest developments include 1,2 1. Lithium salts which are based on the well-known tris(trifluoromethylsulfonyl) methide and bis(trifluoromethylsulfonyl) imide, i.e., variants, such as the cyclic imide Liwhere n ϭ 1-3, 4 the asymmetric methide Li[C(SO 2 CF 3 ) 2 (SO 2 C 4 F 9 )], and the bismethide Li 2 [C 2 (SO 2 CF 3 ) 4 (S 2 O 4 C 3 F 6 )], both synthesized by Sartori et al. 5 2. Lithium imides with new ester type substituents and imides with long fluoroalkyl groups. 6 3. The family of chelatoborates, developed in our laboratory. [7][8][9][10][11][12] 4. A similar class of chelatophosphates where the tetracoordinated boron with two ligands is substitued by the hexacoordinated phosphorous with three ligands. 13 5. A new approach is based on ligands which, instead of solvating cations, 14 displace cations in ion pairs by anion solvation. This is made possible by the strong interaction of the anions with aza-ether compounds. 15 Electron withdrawing substituents such as CF 3 SO 2 Ϫ