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DY: Fachverband Dynamik und Statistische Physik
DY 41: Brownian Motion, Stochastic Processes, Transport II
DY 41.7: Talk
Friday, March 18, 2011, 12:00–12:15, HÜL 186
Gas-induced metal-insulator transition in nanoporous crystalline multilayered metal oxide systems — •Julia Dräger1,2, Stefanie Russ2, Claus-Dieter Kohl3, and Armin Bunde1 — 1Inst. f. Theoret. Physik III, Justus-Liebig-Universität Giessen, Germany — 2Inst. f. Theoret. Physik, Freie Universität Berlin, Germany — 3Inst. f. Angew. Physik, Justus-Liebig-Universität Giessen, Germany
We use a site-bond percolation model to study, both numerically and analytically, the gas-induced metal-insulator transition in thin layers of nanoporous crystalline metal oxides. While below a critical gas concentration Nc the nanoporous structure is insulating due to the absence of a percolating path, which consists of conducting grains (sites) and intergranular contacts (bonds), above Nc the conductance increases rapidly. We find two different scenarios: (i) For systems of high porosity, the transition arises from missing conducting grains, leading to site percolation effects. (ii) For systems of low porosity, the underlying conduction mechanism changes with increasing mean grain-size <D>: For large <D> the transition occurs due to bond- and for small <D> due site percolation effects. While for bond percolation Nc grows linearly with <D>, for site percolation a nonlinear behavior of Nc shows up for very small <D>. Our findings explain the linear dependence of Nc on <D> found in former works, which had not been fully understood before and suggest how the different conduction mechanisms possibly show up in experiments. We furthermore explore how the distribution of grain-sizes influences the shape of the characteristics.