Ionic Conductivity, Structure and Oxide Ion Migration Pathway in Fluorite-Based Bi8La10O27

The oxide ion conductor bismuth lanthanum oxide Bi8La10O27 was studied by a combination of experimental and computational methods, including variable temperature X-ray and neutron diffraction, impedance spectroscopy, and ab initio molecular dynamics simulations. Bi8La10O27 can be readily prepared by conventional solid state routes, and it crystallizes as a fluorite-related Superstructure in space group Immm. It is stable up to 1000 degrees C, and it does not undergo any clear structural phase transition in this temperature region. Bi8La10O27 exhibits oxide ion conductivity of 10(-3)-10(-2) S/cm between 600 degrees C and 1000 degrees C and a decrease of the activation energy from 0.869(8) eV below 600 degrees C to 0.722(3) eV above this temperature, presumably associated with increased mobility of oxide ions due to their local disordering. Ab initio molecular dynamics simulations provide a valuable insight into the conduction process in Bi8La10O27 and identify the crystallographic sites involved in the conduction pathway.