On the Flexibility of the Structural Framework of Cubic LAMOX Compounds, in Relationship with Their Anionic Conduction Properties

A mathematical analysis of the cubic crystal structure of fast oxide-ion conductor β-La2Mo2O9 (and derived members of the LAMOX family) shows that its cationic sublattice can behave as a semirigid framework. Tilt/rotation of rigid [O1La3Mo] anti-tetrahedral units about their 3-fold axis can open up tunnels in the cationic framework, therefore favoring the mobility of O2 and O3 oxide ions located in these tunnels, as confirmed by molecular dynamics simulations. Such a process is likely to assist the anionic transport and explain the postulated transition from Arrhenius-type to VTF (Vogel−Tamman−Fulcher)-type behavior propounded to account for the peculiar conductivity curvature observed at high temperature in all the cubic LAMOX compounds. It also clarifies the correlated extra cell volume expansion observed at the same temperature in all these materials.