Abstract

A new family of fast O²⁻ conductors, which exhibit anionic conductivity comparable to that of stabilised zirconia, is presented. The parent compound of this new family, hereafter called LAMOX, is lanthanum molybdate La₂Mo₂O₉. Various substitutions have been attempted: on the lanthanum site (La_2 − xA_x)Mo₂O₉ with A = Sr, Ba, K, or Bi; on the molybdenum site La₂(Mo_2 − xB_x)O₉ with B = Re, S, W, Cr and V; and on the oxygen site with fluorine. Most of these substitutions suppress the phase transition which occurs in La₂Mo₂O₉ around 580 °C from a low temperature α form to a high temperature (more conducting) β form, and stabilise the β form at room temperature. Several members of the LAMOX series are studied through X-ray and neutron diffraction, and conductivity measurements. Large O²⁻ thermal factors and local static disorder agree well with the anionic nature of the conductivity. Partly vacant sites with short inter-site distances suggest a most probable conduction path with tridimensional character.