Atomic-configuration modeling of ion-conducting crystalline oxide by diffraction technique and theoretical calculation

Since a high ionic conduction in a crystal can be achieved by tailoring point defects generally, an investigation on a defect structure is of much importance in the field of the solid-state electrochemistry. Due to a non-periodic nature of a defect distribution, however, a typical atomic-configuration analysis with the Bragg reflections is insufficient to gain deep understanding on defects in a crystal. In order to get a clear snapshot of an atomic configuration of a crystal with defects, this paper pays special attention on advanced analytical methods using the pair distribution function (PDF) combined with theoretical calculations. The PDF analyses on some ion-conducting oxides succeed in revealing mobile-ion trappings by specific cations. Especially, the reverse Monte Carlo modeling with both the Bragg reflections and convolved structure factors S(Q) enables us to discuss an intermediate-range atomic configuration with a couple of hundreds of atoms, and then visualize mobile-ion distribution in a crystal as a snapshot. An electronic structure computed by the density functional theory can explain well the trapping mechanism of the mobile ions. Such a strategy will shed new light on the defect chemistry and give a breakthrough for discovering a novel ion-conducting crystal.