Temperature dependence of the electron-density and nuclear-density distributions in materials for solid oxide fuel cells

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We have investigated the positional disorder and diffusion path of oxide ions in Bi_2O_3,CeO_2, and (La_<0.8>Sr_<0.2>)(Ga_<0.8>Mg_<0.15>Co_<0.05>)O_<3-δ・>. These were studied through the nuclear density distribution obtained by a combined technique including a Rietveld refinement, a maximum-entropy method(MEM) and MEM-based pattern fitting of the neutron powder diffraction data measured at high temperatures. Oxide ions in fluorite-type structured δ-Bi_2O_3 and CeO_2 have a complicated disorder spreading over a wide area and shift to the <111> directions from the ideal fluorite site at higher temperatures. Diffusion path of oxide ions in (La_<0.8>Sr_<0.2>)(Ga_<0.8>Mg_<0.05>Co_<0.05>)O_<3-δ> perovskite is not along the straight line between the ideal positions, but exhibits an arc shape away from the B-site cation (Ga_<0.8>Mg_<0.5>Co_<0.05>).