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Strain-dependent ionic migration in ZrO2


Electrolytes with high ionic conductivity at lower temperatures are the prerequisite for the success of Solid Oxide Fuel Cells
(SOFC). One promising candidate is doped zirconia. In the past its ionic conductivity has mainly been increased by decreasing its thickness. Here we investigate in the framework of density functional theory, how the migration barriers for oxygen ions respond to a change of the atomic strain. Similar to other publications we observe a decrease in the migration barrier for expansive strain, but in addition we also find an enormous decrease of the migration barrier for high compressive strains. A simple analytic model gives an explanation for this behavior.

(J. A. Hirschfeld, H. Lustfeld)


Dielectric constant and energy storage in metallic electrolyte composites


The already large dielectric constants of some electrolytes like BaTiO3 can be enhanced further by adding (with concentration p) metallic nanoparticles, a factor of more than 1000 is possible near the percolation threshould. Paradoxically, this steep increase of the dielectric constant is not connected to an increase of energy storage, instead a dramatic decrease of energy storage takes place. Based on percolation theory an explanation

(H. Lustfeld, C. Pithan, M. Reißel)


Photovoltaic absorber materials with (almost) unlimited availability


Large scale photovoltaic energy generation necessitates not only a high efficiency of the absorber materials, but also calls for an almost unlimited availability of the used elements and environmental sustainability of the solar cells. We explore compounds of abundant elements by density functional theory and manybody perturbation theory and address not only the absorption properties of the bulk, but also explore its surfaces and interfaces where electrons can get trapped on their way to the front- and back-contacts of the photovoltaic cell. The image on the right shows the charge density of dangling bond states that are formed in the energy gap of iron disilicide. These states lead to a high reactivity of the surface and facilitate the
easy formation of charge trapping layers

(T. Schena, P.Xu and G. Bihlmayer)