Structural and transport characteristics of the LAMOX family of fast oxide-ion conductors, based on lanthanum molybdenum oxide La2Mo2O9

A new family of fast O2- conductors, which exhibit anionic conductivity com parable to that of stabilised zirconia, is presented. The parent compound o f this new family, hereafter called LAMOX, is lanthanum molybdate La2Mo2O9. Various substitutions have been attempted: on the lanthanum site (La(2-x)A (x))Mo2O9 with A = Sr, Ba, K, or Bi; on the molybdenum site La-2(Mo2-xBx)O- 9 with B = Re, S, W, Cr and V; and on the oxygen site with fluorine. Most o f these substitutions suppress the phase transition which occurs in La2Mo2O 9 around 580 degreesC from a low temperature alpha form to a high temperatu re (more conducting) beta form, and stabilise the beta form at room tempera ture. Several members of the LAMOX series are studied through X-ray and neu tron diffraction, and conductivity measurements. Large O2- thermal factors and local static disorder agree well with the anionic nature of the conduct ivity. Partly vacant sites with short inter-site distances suggest a most p robable conduction path with tridimensional character.