The LAMOX Family of Fast Oxide-Ion Conductors: Overview and Recent Results

A short review of our recent works and original results on the new LAMOX family of fast oxide-ion conductors based on La 2 Mo 2 O 9 are presented. The order/disorder phase transition of La 2 Mo 2 O 9 , accompanied by an increase of anion conductivity, is suppressed by most of the substituants which stabilize the highly conducting cubic phase down to room temperature. The series La 2-x R x Mo 2-y W y O 9 (R=Nd,Gd,Y) was studied with respect to the optimisation of anion conduction and stability against reduction. Tungsten substitution is a good way to mi nimize oxygen loss under reducing atmosphere, a drawback in applications such as electrolytes for solid oxide fuel cells. Ball-milling and dilatom etric studies allowed an efficient control and improvement of the samples relative density, for a better characterisation of the oxygen diffusion pro perties, a first account of which is presented here. The LAMOX family exhibits among the highest oxygen tracer diffusion coefficients. A specific curvature in the conductivity curves of cubic substituted phases is interpreted as resulting from a VTF-type conduction mechanism above a certain temperature , an indication of the existence of a dynamic disorder at high T, which would freeze while cooling down.