Poster: Polar Dielectrics, Optics, and Ionics

Ionic conductivity of nanocrystalline heavily acceptor doped ceria: The role of the local atomic order

Acceptor doped ceria (CeO2) is a material that over the years has attracted much interest for applications in solid oxide fuel cells and oxygen membranes. This study aims at systematically investigating how the local atomic order and the dopant distribution affect the ionic transport of nanocrystalline CeO2 ceramics doped with samarium, erbium and ytterbium, with concentrations ranging between 10 and 30 at.%. For this purpose, a.c. electrochemical impedance spectroscopy together with Raman and fluorescence spectroscopy as well as XRD and EXAFS analysis have been carried out. In order to have detailed information on the bulk properties of these compositions also microcrystalline samples have…

CoCoDat: a database system for organizing and selecting quantitative data on single neurons and neuronal microcircuitry.

We present a novel database system for organizing and selecting quantitative experimental data on single neurons and neuronal microcircuitry that has proven useful for reference-keeping, experimental planning and computational modelling. Building on our previous experience with large neuroscientific databases, the system takes into account the diversity and method-dependence of single cell and microcircuitry data and provides tools for entering and retrieving published data without a priori interpretation or summarizing. Data representation is based on the framework suggested by biophysical theory and enables flexible combinations of data on membrane conductances, ionic and synaptic current…

The first principles calculations of the atomic and electronic structure of cubic and orthorhombic LaMnO3 surfaces

Combining GGA-plane wave approach as implemented into the VASP - 4.6.19 computer code with a slab model, we studied in detail the atomic and electronic structure of the LaMnO3 surfaces, in both cubic and orthorhombic phases. The results obtained are compared with similar studies for other ABO3-perovskites.

Technical challenges in the construction of the steady-state stellarator Wendelstein 7-X

The next step in the Wendelstein stellarator line is the large superconducting device Wendelstein 7-X, currently under construction in Greifswald, Germany. Steady-state operation is an intrinsic feature of stellarators, and one key element of the Wendelstein 7-X mission is to demonstrate steady-state operation under plasma conditions relevant for a fusion power plant. Steady-state operation of a fusion device, on the one hand, requires the implementation of special technologies, giving rise to technical challenges during the design, fabrication and assembly of such a device. On the other hand, also the physics development of steady-state operation at high plasma performance poses a challeng…

Electronic modifications in (Ba,La)(Fe,Zn,Y)O3−δ unveiled by oxygen K-edge X-ray Raman scattering

Oxides with mixed protonic-electronic conductivity are relevant as oxygen electrodes for protonic ceramic fuel cells and electrolyzers. We investigate the modification of the electronic structure of (Ba,La)(Fe,Zn,Y)O3−δ when iron is partially replaced by Zn2+ or Y3+ and when it changes between 3+ and 4+ formal oxidation states. With a combination of X-ray Raman scattering (O K-edge) and X-ray absorption near edge structure (Fe, Zn, and Y K-edges) and the corresponding simulations reproducing the spectroscopic data, we quantitatively analyze the degree of covalency of the Fe-O bonds in reduced (Fe mainly 3+) and oxidized (Fe mainly 4+) materials. The simulations employ two semi-empirical par…

The Role of the Local Atomic Order and Boundary Effects on the Electrical Transport of Ceria

Heavily acceptor doped ceria is a material of great relevance for applications in solid oxide fuel cells and oxygen membranes. Depending on the operation temperature, dopant concentration and microstructure (e.g. nanocrystalline vs. microcrystalline), the ionic transport properties of ceria can be mostly hindered by (i) grain boundaries or (ii) local atomic disorder in the bulk. Here, we present a selection of examples (ranging from thin films to ceramics) of how and to which extent these effects can affect the electrical transport properties. Emphasis will be given to the case of heavily doped nanocrystalline and microcrystalline ceria doped with samarium, erbium and ytterbium (dopant conc…