THE STRUCTURE OF THE OXIDE-ION CONDUCTOR LA0.9SR0.1GA0.8MG0.2O2.85 BYPOWDER NEUTRON-DIFFRACTION

High resolution powder neutron diffraction has shown that the room tem perature structure of the new fast oxide ion conducting solid electrol yte La0.9Sr0.1Ga0.8Mg0.2O2.85 is monoclinic, rather than orthorhombic, as for the undoped parent phase LaGaO3. In both systems the main dist ortion of the structure from the ideal perovskite is the tilting of th e GaO6 octahedra, and the symmetry change has a direct effect on this tilting, such that for LaGaO3 the [001](p) tilt is in-phase when succe ssive octahedra are considered, while for La0.9Sr0.1Ga0.8Mg0.2O2.85 it is antiphase. The degree of tilting of the octahedra is also reduced by the doping. For this room temperature data, the oxygen vacancies in La(0.9)Sr(0.1)Ga(0.8)Mg(0.2)O(2.85)are shown to be preferentially loc ated in the apical sites. (C) 1998 Elsevier Science B.V. All rights re served.